Programmable thermostat

A programmable thermostat features a memory unit receptive of unit values of temperature desired at different times on different days all individually or in various combinations both as to days and times. An output device signals a temperature control system. As controlled by a clock, the memory unit is addressed during different times of the different days to provide a signal representing the corresponding value desired. Existing temperature level is sensed and compared with each value so as to develop an error signal. In response to that error signal, the output is operated in a direction to reduce the difference between actual and desired temperatures. Numerous details as to layout, construction and circuitry are presented.

The present invention relates to a programmable thermostat. More 
particularly, it pertains to a variety of system, circuitry and mechanical 
aspects of a unit for governing the program of temperature control within 
a building or other space. 
As confirmed by many studies, substantial savings in energy usage may be 
obtained through appropriate adjustment of heating and cooling units to 
govern their operation in accordance with actual requirements. It has been 
demonstrated that the mere act of reducing a household thermostat level 
during sleeping hours can result in worthwhile savings in the cost and use 
of energy. Analogously, there may be other times during the total day in 
which adjustment of thermostat control advantageously could be modified in 
order to accommodate such things as level of activity, presence within the 
space concerned and the like. 
It has long been known to associate a thermostat with a clock-actuated 
device which automatically turns down the temperature level sought during 
normal sleeping hours. Such devices typically are programmable only to the 
extent of allowing a manually fixed change of temperature that is applied 
to every day of the week. 
It also is known, nevertheless, to program a given temperature-determining 
system by varying the energization of the controlling unit in accordance 
with selected time schedules. In addition, it has been recognized that 
electronic components are available for the purpose of replacing the 
mechanical clocks formerly associated with such controls and also to 
provide an illuminated display of the temperature conditions under 
observation and control. 
Notwithstanding the aforementioned general recognition of the desire to be 
able to control temperature conditions within a space and the provision of 
time-controlled devices for automatically dictating changes in operation, 
that which has heretofore been suggested seems to have suffered from a 
lack of flexibility in its manner of control, substantial cost of 
implementation, and either complete dependence upon existing power sources 
or the need for a cumbersome auxiliary power source. 
With the advent of the microcomputer contained within a very small package, 
it has become apparent that the control and operation of many different 
appliances and the like may be enhanced, both as to flexibility of control 
and efficiency, by incorporating the techniques associated therewith. 
Joined with other solid-state components for controlling significant 
amounts of power, the microcomputer has "opened the door" to an almost 
unlimited variety of improvements in various devices that previously were 
operated by means of mechanically-operated switches sometimes associated 
with such familiar apparatus as relays and solenoids for the purpose of 
ultimately handling the higher power levels involved with different 
machines and appliances. 
It is a general object of the present invention to take advantage of the 
aforedescribed development of the art in order to provide a new and 
improved thermostat. 
Another object of the present invention is to provide new and improved 
implementations of electronics circuitry advantageously usable in 
achieving the general objective. 
A further object of the present invention is to provide a new and improved 
approach to thermostat control. 
Still another object of the present invention is to provide a new and 
improved mechanical assembly for a thermostat and its systems. 
In accordance with one aspect of the invention, a programmable thermostat 
includes a memory unit together with means for entering into that memory 
unit values of temperature desired at different times on different days of 
a week all individually and in various combinations of days and times 
involved. An output device controls one or both of heating and cooling 
systems. All operation is governed by a clock. Under control of the clock, 
the memory unit is addressed during the different times of the different 
days so as to provide a signal representative of the unit value for 
temperature. At the same time, existing temperature is sensed. That value 
signal is compared with the existing temperature level so as to develop an 
error signal. In response to the error signal, the output device is 
operated in an appropriate manner to reduce the magnitude of the 
difference between actual and desired temperatures. The invention also 
includes numerous details of improved circuitry and of housing for 
enclosing the circuitry and making the entire thermostat desirable for 
implementation and usage.

In the foregoing description of the figures, the terms "top" and "bottom" 
have reference to the thermostat in the orientation of FIG. 9 as, for 
example, sitting on a table. In use most of the time, the "bottom" of the 
thermostat usually will be face-to-face with a vertical wall. 
FIG. 1 depicts an overall system. It includes power supply and switching 
circuitry 100, a battery monitor 102, a timer 104, a microcomputer and 
clock 106, a temperature sensor 108, a keyboard 110 and a display 112. As 
indicated, unit 100 has power, control or other connection to the 
remaining components of the system. In general, all of the illustrated 
"blocks" interact with each other. A detailed implementation of the system 
of FIG. 1 is depicted in FIGS. 2-5. 
As specifically embodied in FIGS. 2-5, it is assumed that there is to be 
adaptation to a conventional heating and/or cooling apparatus which 
involves a twenty-four volt control system for operational purposes. That 
is, primary operating power for the particular embodiment disclosed herein 
is intended to be derived from an existing heating or cooling unit as 
normally would be available at the site desired for a thermostat. In 
addition, there would be present at that site wiring intended to energize 
a solenoid or the like which controlled operation of a furnace and there 
also may be wiring which would similarly energize an air cooler and, often 
separately, its fan or blower. In the conventional twenty-four volt 
control system for many heating and cooling units, the controlled solenoid 
is connected directly in series with the secondary winding of a step-down 
transformer. Consequently, only two wires between the controlled unit and 
the thermostat are necessary to permit both energization of the solenoid, 
by switching contained in the thermostat, and the supply of power from the 
transformer to the thermostat. While the specific embodiment is 
particularly configured to permit direct connection to that type of 
conventional system, its interfacing circuitry may readily be modified to 
accommodate other control arrangements that require three-wire or 
four-wire interconnection between the thermostat and the controlled unit. 
In addition, other ultimate applications are available, and they may 
require modification. For example, the overall system might be adapted to 
govern a heat-control system that did not, in itself, provide necessary 
input power for the herein disclosed apparatus. In that case, of course, a 
separate transformer would be included between a power source and this 
apparatus. Also, the associated heating or cooling apparatus might not be 
subject to the normal twenty-four volt control system. An example would be 
now-conventional resistance-heated space-warming systems that operate from 
conventional building supplies at one-hundred-twenty or two-hundred-forty 
volts. In such a case, an adaptor unit would be interposed between that 
which is illustrated and the supply to the heating elements, typically 
involving relays or solenoids for switching higher levels of voltage 
and/or current. Alternatively, the comparatively low-power solid-state 
output switches hereinafter described would be replaced with higher-power 
devices. While not forgetting those clear alternatives, the description 
hereinafter will proceed on the basis of interface with an at least 
somewhat more ordinary heating or cooling system each of which employs 
two-wire twenty-four volt control and supply for primary operation and, 
perhaps, an added wire for separate blower operation. 
Generally with regard to FIGS. 2-5, different individual components have 
been denominated by the use of nomenclature which has become conventional 
in the art. Thus, a capacitor is denoted by the letter "C" and a resistor 
by the letter "R". Additionally, numerous ones of the different components 
are incorporated within standard integrated circuits formed on so-called 
chips each of which includes a number of such components. Labeling has 
been employed to indicate which of those components are in common on the 
same chip. For example, the label IC3 is applied to several different 
components, as will hereinafter be individually identified, to indicate 
that they all are embodied herein as a portion of the same chip. 
Throughout the drawings, various numerals appear adjacent to different 
terminals but without lead lines. These always refer to conventional 
manufacturer's designations with regard to the components concerned. For 
example, within each rectangular block that represents a 
commercially-available component, there is a series of numbers; those are 
the pin numbers assigned as a standard practice with respect to such 
components. A lightening-flash symbol is used to indicate optical coupling 
to another component, and those two components will have the same "IC" 
designation. 
Where a terminal is not otherwise denominated, connection as between 
different ones of FIGS. 2-5 may be traced by the use of a letter or number 
in one figure which corresponds with the same letter or number utilized in 
a related figure. In addition, various test points are indicated by 
terminals labeled with the symbol "TP" plus a number. These are for use in 
testing and servicing and will not be further mentioned. 
The power supply and switching arrangement 100 is detailed in FIG. 2. A 
terminal 120 connects to the available twenty-four volt source provided by 
the heating system, such as a furnace, to be controlled. A terminal 121 
supplies a control voltage or signal back to the heating unit for enabling 
its energization. Typically, the signal from terminal 121 energizes a 
solenoid at the furnace which opens its main fuel supply or otherwise 
causes the heating unit to activate and develop its desired heat output. 
Bridging terminals 120 and 121 is a TRIAC 123 the gate of which is 
connected to the collector of an opto-transistor 124 and the emitter of an 
opto-transistor 125. Also bridging terminals 120 and 121 is the series 
combination of a resistor R35 and a capacitor C16. In a known manner, 
these serve as a snubber network to prevent misfiring of TRIAC 123 by 
reason of the voltage-current phase relationships. The emitter of 
transistor 124 is returned to terminal 121 through a diode D1, and its 
base is connected to its emitter by a resistor R33. The collector of 
transistor 125 is returned through a diode D3 to terminal 121, while its 
base is connected back to its emitter by a resistor R34. Diodes D1 and D3 
provide protection for transistors 124 and 125 against reverse bias. Also 
bridging terminals 120 and 121 are the input terminals of a bridge 
rectifier 126 in series with a resistor R4 that is shunted by a capacitor 
C10. The negative output terminal of rectifier 126 is connected to ground, 
while its positive output terminal is connected to a supply bus 127 that 
extends to the input terminal of a Darlington transistor 128. The output 
terminal of transistor 128 is connected to a terminal 129 and provides a 
sub-component supply voltage Vcc. 
The input of transistor 128 (also Q3) is shunted by a resistor R16 and the 
input base is returned to ground (GND) or Vdd through a zener diode VR2. 
The output emitter of transistor 128 is coupled to ground over a capacitor 
C12. A capacitor C11 is coupled between the input side of transistor 128 
and ground. 
A capacitor C3 is coupled from bus 127 to ground through resistors R8 and 
R9 with the series combination of those resistors being shunted by a 
capacitor C2. Coupled to the junction between capacitor C3 and resistor R8 
is one side of an opto-TRIAC 132 the other side of which is returned to 
output terminal 121. A pair of resistors R14 and R15 extend in series 
between the output of transistor 128 (Vcc) and ground. The junction 
between resistors R14 and R15 is connected to the plus inputs of each of 
comparators 133 and 134. The minus input of comparator 133 is connected to 
the junction between resistors R12 and R13 which form a voltage divider 
extending between bus 127 and ground. The minus input of comparator 134 is 
connected to the junction between resistors R8 and R9. 
Three different opto-diodes 135, 136 and 137 are optically coupled to the 
input or gate of respective opto-TRIAC 132 and opto-transistors 124 and 
125. Diode 136 is connected from the output terminal of comparator 133 
through resistors R31 and R10 and diode 135 to ground. Diode 137 is 
connected from the output terminal of comparator 134 through a resistor 
R11 to the junction between resistors R10 and R31. The different Vcc 
leads, such as through terminal 129, are coupled to ground by a capacitor 
C13 connected physically close to the Vcc terminal of microcomputer 106. 
When control of an air conditioner is desired in addition to control of a 
furnace or other heating unit, unit 100 includes a module 138 which 
presents output terminals 139, 140 and 141. Terminal 139 supplies power to 
run the air conditioner, and terminal 140 separately supplies power to the 
fan of that air conditioner. A switch 142 may be closed to bridge 
terminals 139 and 140 when operation of the fan is to be automatic and to 
bridge termimals 140 and 141 to command continuous fan operation. Terminal 
141 receives the conventional twenty-four volt control potential available 
from such an air conditioner or, in the alternative, is connected by a 
jumper 143 so as to be connected to the twenty-four volt input available 
from the heating unit. Connected between terminals 141 and 139 is a TRIAC 
Q4 the gate of which is returned through an opto-TRIAC 144 to terminal 
139. The optical-input gate of TRIAC 144 is coupled to an opto-diode 144a 
(FIG. 4). 
Operation of the power supply and switching system of FIG. 2 is enabled by 
a signal which arrives through a terminal 145 that is connected to the 
junction between resistors R10 and R31. The system is designed so that 
approximately eighty-five percent of the available power input is 
transferred through TRIAC 123 for purposes of energizing the solenoid or 
other actuator in the furnace. At the same time, the amount of monitoring 
power required by the system is sufficiently low to avoid false actuation 
of the furnace solenoid. 
When the system of FIG. 2 is in the "off" mode, rectifier 126 still changes 
the twenty-four volt alternating-current input into direct current. In 
this mode of operation, all of the optically-coupled devices are disabled. 
The output direct current from rectifier 126 is stored across the 
combination of capacitors C2 and C3. Regulation of the output voltage is 
achieved by means of the series combination of resistor R16 and diode VR2. 
In conjunction with Darlington transistor 128, of course, the output 
circuit exhibits a high gain, so that a substantial degree of voltage 
stability is obtained. Accordingly, the internal operating potential Vcc 
is available during the "off" mode of operation for energizing all of the 
other components and sub-systems. 
The "on" mode of operation serves to fire TRIAC 123 and thus deliver the 
twenty-four volt alternating-current supply voltage directly on to the 
heater solenoid or other activator that controls operation of the furnace 
or other source of heat. When TRIAC 123 is fired to supply the output 
operating potential to the heating unit, it is still necessary that power 
be maintained in the controller as developed by rectifier 126. To this 
end, TRIAC 123 is triggered part way into each half cycle of supplied 
input power and after charging capacitors C2 and C3. 
Comparators 133 and 134 are used to monitor the voltages across capacitors 
C2 and C3. For effective operation with a regulated output voltage Vcc of 
nine volts, typical operation requires that the voltage on C3 available at 
the input terminal of transistor 128 should rise to approximately twenty 
volts at the beginning of each half wave. This allows the current drain of 
the unit to discharge capacitors C2 and C3 during the remainder of each 
half wave without affecting the regulated output voltage Vcc. 
The voltage divider established by resistors R14 and R15 serves to supply 
comparators 133 and 134 with a reference voltage, in the instant system of 
approximately 4.5 volts. The enabled input through terminal 145 is in a 
"high" state when heating is demanded. 
The waveform as exhibited across TRIAC 123 is shown in FIG. 6. As the 
potential increases on each negative half-wave, current is enabled to flow 
through TRIAC 132 in order to charge capacitor C2, the return being 
established to the other side of the incoming alternating-current line 
through rectifier 126. The divider established by resistors R8 and R9 is 
selected so that, when capacitor C2 is charged to ten volts in this 
example, the voltage on the negative input of comparator 134 becomes equal 
to the reference voltage of 4.5 volts. When capacitor C2 becomes fully 
charged, during the negative half wave of the input cycle, to just above 
ten volts, the output of comparator 134 switches to "low". That allows 
current in the enabling signal through terminal 145 to flow through 
resistor R11 and light-emitting-diode (LED) 137. 
As indicated above, diode 137 is an opto-coupler, such as a 4N30, of which 
transistor 125 is an optically-coupled part. During the negative half wave 
of the incoming power, the "low" side of the effective alternating-current 
line is positive with respect to the gate of TRIAC 123. Accordingly, when 
capacitor C2 is charged to just above the ten-volt level mentioned, 
comparator 134 switches its output state. Current then is allowed to flow 
through diode 137 and the optical output from diode 137 activates 
transistor 125, so that current flows through the latter and diode D3 into 
the gate of TRIAC 123. That triggers or fires the latter and achieves the 
ultimate result of connecting terminals 120 and 121. At this point, 
capacitor C2 discharges to a value below ten volts. That deactivates diode 
137 and allows TRIAC 123 to reset to its open state on the next zero 
crossing of the waveform. 
On the positive half wave of each cycle of the input alternating-current 
supplied, current flows through rectifier 126 and begins to charge 
capacitor C3. That current flows through opto-TRIAC 132 back to the "low" 
side of the alternating-current input system. The divider of resistors R12 
and R13 establishes a reference such that, when the voltage level on bus 
127 reaches twenty volts, the output of comparator 133 switches to a "low" 
state. With capacitor C2 charged as described previously, C3 is then 
charged to a value of ten volts to cause comparator 133 to switch to "low" 
and draw current through terminal 145 by way of resistor R31 and 
light-emitting diode 136. The optical emission from the latter is coupled 
into its associated transistor 124, so as to cause the triggering of TRIAC 
123 by allowing current to flow from the gate of the latter through 
transistor 124 and diode D1. Shortly after TRIAC 123 is triggered, the 
output of comparator 133 switches to "high" and, thereby, allows TRIAC 123 
to once more reset on the next zero crossing. 
During operation on either half cycle, light-emitting diode 135 is 
triggered by the signal received over terminal 145, so as to activate its 
associated TRIAC 132 by means of the optical coupling between those two 
elements. It will be observed that the system of FIG. 2, including 
capacitors C2 and C3, is actually a voltage-doubling network that utilizes 
what amounts to approximately ten volts of the input alternating-current 
waveform on each half cycle to achieve a total of about twenty volts 
applied to the regulation system which includes diode VR2 and transistor 
128. Resistors R33 and R34 preferably are included merely as noise 
suppressors so as to prohibit false triggering of transistors 124 and 125. 
Referring again to FIG. 6, it may be seen that a favorable short-term 
instability occurs. The first two or three cycles of the 
alternating-current waveform that occur after the signal received through 
terminal 145 goes "high" are entirely shunted across the system. That 
occurs because the total voltage across the combination of capacitors C2 
and C3 prior to that "high" signal is equal to the peak voltage of the 
alternating-current input which, in the example given, is approximately 
thirty-five volts. Therefore, the outputs of comparators 133 and 134 
remain "low" until capacitors C2 and C3 discharge to the desired level. 
At the heart of the overall temperature control system herein under 
description is a microcomputer 150 as shown in FIG. 4. While its function 
will be described in more detail hereinafter, it may be noted that it 
supplies, from a terminal 2, the signal which, after processing also yet 
to be described, provides the enable control signal fed through terminal 
145 to the unit of FIG. 2 that has just been discussed. 
For the purpose of operating module 138 to achieve control of an associated 
air conditioning unit, microcomputer 150 also yields an enable output as 
its pin 3 that is fed in series through a resistor R36 and LED 144a which 
is returned to ground. LED 144a is optically coupled to control the 
operation as a gate input of TRIAC 144 in module 138. Upon the occurrence 
of a "high" from microcomputer 150, therefore, TRIAC 144 supplies a signal 
to the gate of TRIAC Q4, so as to apply the basic twenty-four volt control 
potential from terminal 141 to terminal 139. 
LED 144a and resistor R36 are included in a module 138a. With operation 
using a REVIEW pushbutton and a permanent program loaded into 
microcomputer 150 as described below, actuation of that pushbutton 
temporarily disables LED 144a and, thus, operation of the air conditioner. 
When that function is not desired, the permanent program may be changed 
accordingly, so that LED 144a stays on during the review procedure. 
Alternatively, the circuit of a module 138a', as shown in FIG. 4B, is 
substituted for module 138a. 
In FIG. 4B, LED 144a is again connected between ground at a terminal 220 
and one end of resistor R36. The other end of resistor R36 is connected 
through a diode D15 to receive the output from the output terminal J9' at 
pin 3 of microcomputer 150. Extending also from that pin 3 is the series 
combination of a resistor R40 and a capacitor C17 that returns to ground. 
Connected to the junction between resistor R40 and capacitor C17 is one 
input of a comparator 146 the other input of which is connected by a 
terminal 148 to a ground return through a resistor R32 from a pin 11 of a 
display driver 164 described more fully below. The output of comparator 
146 is connected to the combined inputs of paralleled comparators 147a and 
147b, their combined outputs being connected through a diode D17 to the 
junction between resistor R36 and diode D15. Those combined outputs also 
are connected through the series combination of a diode D16 and a resistor 
R38 back to the junction between resistor R40 and capacitor C17. Another 
comparator 149 on the same chip with the others is disabled by connecting 
both of its inputs to ground. Energization of the comparators is by way of 
a connection to terminal 216, as indicated, and a ground return. 
Also added along with module 138a' is a resistor R26 connected between 
ground and an output terminal J5 at pin 26 of microcomputer 150, along 
with a resistor R30 connected between output pins 17 and 22 (Vcc) of 
driver 164. In operation, LED 144a continues to be energized as before 
when a "high" occurs on output pin 3 of microcomputer 150, and that signal 
also is stored on capacitor C17. When that output goes "low" as driver 164 
is activated, the changed level on terminal 148 enables energization of 
LED 144a through diode D17. The latter condition is latched on by diode 
D16 which holds the signal on capacitor C17. 
It is believed to be desirable that the components of module 138, 
separately or together with resistor R36 and diode 144a as module 138a (or 
with module 138a'), be physically incorporated into the overall 
arrangement as at least somewhat separate sub-assemblies. This permits the 
overall system to be manufactured without modules 138 and 138a (or 138a') 
for use in the application of controlling only a heating unit. When the 
additional control of air conditioning or cooling also is desired, 
however, it will be immediately apparent how easily and inexpensively it 
is to add these other modules so as to employ the same overall system to 
accomplish that additional function of control. 
As is now generally known with respect to the implementation of 
microcomputers such as unit 150, they establish an operating procedure 
which first of all is ordained by their specific design and also is 
established by "loading" or permanent programming at the factory level, so 
as to exhibit a defined response to ultimate changeable programming by the 
user. In terms of information-handling capability, a single solid-state 
microcomputer can perform tasks previously assigned literally to a roomful 
of computer apparatus. Perhaps the only drawback of the present day 
microcomputer is that its user-supplied variable storage of input 
information is subject, by reason of its manner of approach, to complete 
erasure upon loss of supply power to this fantastic device. Thus, a user 
program of temperature control entered into microcomputer 150 could be 
lost during a power shortage when the normal supply potential at terminal 
120 was terminated. Also, dependence upon the supply at terminal 120 would 
prohibit any kind of remote use of the unit herein under discussion. 
To overcome the just-mentioned lack of permanent user-programmable storage 
in microcomputer 150, the present system includes a battery and monitoring 
circuit therefor as shown in FIG. 3. At the outset, the arrangement of 
FIG. 3 includes a battery 152 in series with a reverse-bias-protecting 
diode D2 and with that series combination being connected between ground 
and the wiring which carries the internal supply voltage Vcc. Without 
more, battery 152 serves to insure that the internal component-supply 
voltage is maintained regardless of the development in unit 100 of that 
same internal supply voltage by way of rectifier 126. The power available 
from battery 152 serves to maintain microcomputer 150 in its condition of 
preserving a user-program whenever the incoming external supply voltage is 
interrupted and whether intentionally or not. 
Of course, any battery is subject to deterioration over a period of time 
even if never used. In accommodation, the system in FIG. 3 serves to 
monitor the battery voltage and provide a necessary signal to 
microcomputer 150 to indicate the impending failure of the battery. To 
this end, a series of components are distributed so as to extend basically 
between a Vcc bus 154 and ground. Thus, a voltage divider composed of 
resistors R5 and R6 extends between bus 154 and ground, resistor R6 being 
bypassed to ground by a capacitor C6 and resistor R5 being bypassed by a 
diode D14. The junction between resistors R5 and R6 is connected to the 
negative input terminal of a comparator 155. That junction is also 
connected through a resistor R22 to the collector of a transistor Q6 the 
emitter of which is returned to ground and the base of which is connected 
through resistors R21 and R28 back to bus 154. 
Another voltage divider, composed of series-connected resistors R2 and R3, 
is connected from the junction between battery 152 and diode D2 back to 
ground. In turn, the junction between divider resistors R2 and R3 is 
connected to the negative input terminal of a further comparator 156. A 
transient suppressor TS1 is shunted across the overall combination of 
resistors R2 and R3 for protection from static electricity discharged into 
the battery terminals. Also bridged between bus 154 and ground is the 
series combination of a resistor R7 and a zener diode VR1, with the 
junction between resistor R7 and zener diode VR1 being connected to the 
positive inputs of comparators 155 and 156. 
The output terminal of comparator 155 is connected between the junction 
between resistors R21 and R28 and from there through a diode D9 and a 
terminal 157 to the initiating (INIT) terminal 9 of microcomputer 150. A 
capacitor C14 is shunted between terminal 157 and ground through a 
terminal 158. Bus 154 is connected through a terminal 159 into the Vcc 
lead. The output terminal of comparator 156 is connected through a diode 
D8 and through a terminal 160 to an input terminal K2 of microcomputer 
150. The output from comparator 156 also is connected through a resistor 
R29 and a terminal 162 to an output terminal 25 (J4) of microcomputer 150 
for the purpose of providing a momentary sensing of battery condition when 
output terminal 25 is in the "high" state. 
In the monitor as shown in FIG. 3, it is comparator 156 which is used to 
detect the low-battery condition. With the output from terminal 25 of 
microcomputer 150 set to a "high", a reference level is established on the 
output of comparator 156 and against which that comparator must work. 
Battery voltage is divided by resistors R2 and R3 and appears on the 
negative input of comparator 156. The relative values of resistors R2 and 
R3 are selected such that, if the battery voltage is above a predetermined 
amount, about seven volts, the voltage at that negative input of 
comparator 156 is above the lower voltage established by diode VR1, so 
that the comparator output is maintained in a "low" state. When, however, 
the battery voltage drops below the predetermined value, the negative 
input to comparator 156 falls below the threshold established by diode VR1 
on the positive input of that comparator. Consequently, the output of the 
comparator then is pulled "high" through R29 connected to terminal 25 of 
microcomputer 150, and that "high" appears as an input at terminal K2. 
Diode D8 serves as a reverse-bias protection against an input from keyboard 
assembly 110 yet to be described. Before discussing keyboard 110 and 
display 112 in detail, it may be noted that, if a logic one is detected on 
the input K2 from keyboard assembly 110 to terminal 6 of microcomputer 
150, while the signal from terminal 25 of microcomputer 150 is high, the 
program is set up to display a warning to the user that the battery should 
be changed. That warning is visibly indicated on display unit 112 upon 
depression of either one of START or REVIEW pushbuttons yet to be 
discussed. 
In operation, the "high" signal from terminal 25 of microcomputer 150 
occurs only about once every four seconds during normal use and for a 
period of time sufficient only to enable the operation of the battery 
monitoring function. As indicated in FIGS. 4 and 5, that output from 
terminal 25 also is utilized as a drive signal connected at J4 of display 
driver 164. Diode D2 serves to prevent the supply voltage from affecting 
the reading by the monitor of battery voltage and also prevents charging 
of the battery. 
Comparator 155 continually monitors the supply voltage available to 
microcomputer 150. With a specified minimum supply voltage for the 
particular microcomputer employed, the microcomputer may continue to run 
at a lower voltage but will not necessarily follow the program contained 
in its read-only memory (ROM). It is, therefore, important that 
microcomputer 150 be held in a reset mode in case of the existence of a 
below-minimum supply voltage. To this end, resistors R5 and R6 divide the 
voltage between ground and bus 154 in order to supply the negative 
potential to comparator 155. The values of resistors R5 and R6 are 
selected such that, when the supply voltage equals the specified minimum, 
the potential present on the negative input of comparator 155 is slightly 
less than that established by the voltage regulating action of zener diode 
VR1. When, however, the supply voltage is below the established minimum 
limit, the output of comparator 155 is held "high" through resistor R28. 
That circumstance forces microcomputer 150 to a reset mode by way of the 
connection through diode D9 to terminal 9 of microcomputer 150. At the 
same time, there is an additional connection to ground resistor R5 by way 
of transistor Q6 which is turned on when the output of comparator 155 goes 
"high". The overall effect is to set microcomputer 150 into a reset mode 
until such time as the supply voltage returns to a value sufficiently 
above the established minimum level by about 0.3 volt. 
It will be noted that the resetting of microcomputer 150 can only occur at 
such time as the incoming twenty-four volt alternating-current supply is 
lost and operation is being maintained from battery 152. Incidentally, 
capacitor C6 also is included so as to initiate the reset condition upon 
the initial supply of power in energization of the overall unit. Finally, 
comparator 155 is depicted as having a direct connection to bus 154, and 
comparator 156 is shown to have a direct connection to ground. These are 
the common power supply connections for all of the comparators on a chip 
IC3. 
Turning now to timer 104 as also shown in FIG. 3, it develops a sixty Hertz 
square wave used by microcomputer 150 in order to keep track of time. A 
sample of the input alternating-current waveform as received at terminal 
120 (FIG. 2) is conveyed by way of terminal 170 through a zener diode VR3 
and a capacitor C7 to the input base of a transistor Q5. The junction 
between diode VR3 and capacitor C7 is shunted to ground by way of the 
parallel combination of a resistor R41 and a capacitor C8 through a 
terminal 172. 
The collector of transistor Q5 is connected to bus 154 which extends to a 
power terminal shown on an inverter 174. Analogously, a terminal on an 
inverter 175 is connected to ground. These are the common power supply 
terminals for all of the inverters on a chip IC2. A capacitor C15 shunts 
bus 154 to ground. 
The emitter output of transistor Q5 is connected to the input terminal of 
inverter 174 and the output terminal of that inverter is, in turn, fed to 
the input terminal of inverter 175. The latter has its output terminal 
connected through a diode D5 to a terminal 176 which, as will be seen in 
FIG. 4, is connected to a microcomputer input pin 5 or K1 to which a 
terminal of keyboard 110 also is connected. The output of inverter 175 is 
fed back over a capacitor C1 to the input of inverter 174, and inverter 
174 is bridged by the series combination of a resistor R37 and a 
potentiometer P1. 
Inverters 174 and 175 serve together as associated components of a 
free-running oscillator that is set to perform at sixty Hertz by means of 
adjustment of potentiometer P1. Because temperture variations may induce a 
drift in that pre-set frequency, the free-running mode of operation of 
timer 104 is used only during periods of power loss at terminal 120 (FIG. 
2). When supplied alternating-current power is available at terminal 120, 
the operation of timer 104 is synchronized to the incoming waveform 
sampled through capacitor C7. 
The waveforms present at the cathode of diode VR3 are shown in FIGS. 7 and 
8. FIG. 7 depicts the waveform whenever the overall heating system is in 
the "off" mode. At the time represented by t1, the input voltage has risen 
slightly to the value at which diode VR3 begins to conduct. From the time 
t1 to the time t3, at the peak of the sine wave, the voltage developed 
across resistor R41 and capacitor C8 builds up in accordance with the 
waveform. The differential of that waveform is conveyed over capacitor C7 
to the base of transistor Q5, so as to enable conduction of that 
transistor and cause charging of capacitor C1 to the supply voltage. The 
latter occurrence forces the output of the resulting oscillator circuitry 
to be synchronized to the incoming line frequency. 
When the overall heating system is in its "on" mode, the voltage waveform 
presented at the cathode of diode VR3 is generally that shown in FIG. 8. 
In this manner of operation, conduction of transistor Q5 occurs from a 
time t4 through a time t5. As a result, the oscillator again is 
synchronized to the sixty Hertz incoming line frequency. Output diode D5 
preferably is included in order to prevent destruction of another signal 
that is present on microcomputer input terminal K1 when the oscillator 
output is low. 
Being temperature responsive, the overall system, of course, requires 
temperature sensor 108. To this end, a temperature-dependent oscillator 
arrangement includes series connected inverters 180 and 181. The input to 
inverter 180 is enabled through a terminal 182 and a diode D6 connected to 
an output terminal at pin 26 or J5 of microcomputer 150 as shown in FIG. 
4. The output of inverter 181 is connected through a diode D7 and through 
a terminal 183 back to pin 8 or K8 of microcomputer 150, which pin also is 
connected to a terminal of keyboard 110 as indicated in FIG. 5. 
The input of inverter 180 is connected to the series combination of a 
resistor R17 and a capacitor C4 to the output of inverter 181. The 
junction between inverters 180 and 181 is connected to the junction 
between resistor R17 and capacitor C4 by the series combination of a 
resistor R18, a potentiometer P2 and a resistor R19. Most importantly, 
resistor R19 is shunted by a thermistor RT1. 
Inverters 180 and 181, together with the associated components, constitute 
another oscillator. Its frequency is determined by the combined values of 
potentiometer P2, resistors R18 and R19 and thermistor RT1 along with 
capacitor C4. Resistors R18 and R19 serve to linearize the operation of 
thermistor RT1 over the desired temperature range. 
When the output from microcomputer 150 as presented at terminal 26 is 
"high", sensor 108 is enabled. The number of pulses which end up appearing 
as an input to terminal 8 of microcomputer 150 (protected by diode D7) are 
counted over a full number of sixteen cycles of pulses as received by the 
microcomputer from timer 104. By mathematical manipulation in the 
permanent program, as will be apparent later, that count is used to 
determine the ambient room temperature and to enable decisions to be made 
as to enablement or disablement of either the heating or air conditioning 
systems that are ultimately controlled. For the present system, that which 
has been illustrated may be specified to an accuracy of less than plus or 
minus one degree Fahrenheit over a range extending between fifty degrees 
Fahrenheit and eighty-nine degrees Fahrenheit. 
As shown on the lower portion of FIG. 5, keyboard 110 is composed of a 
four-by-four matrix of normally-open switches that are pushbutton 
operated. Six of the switch pushbuttons are labeled in that figure with 
the terms STORE, START HEAT, START AIR, REVIEW, CLEAR, and AM/PM. The 
remaining buttons respectively are marked with the numbers zero through 
nine and also, as can be viewed in FIG. 10, have lettering which, as will 
be further discussed below, corresponds to different ones of the days of 
the week and different combinations of such days. 
The matrix includes columns J0, J1, J2 and J3, together with rows K1, K2, 
K4 and K8. The buttons are distributed so as individually to bridge the 
respective different intersections within the array with two exceptions as 
shown. That is, both the STORE and the START HEAT buttons bridge the 
intersections between the column J0 and row K8, and the START AIR button 
bridges between column J0 and a terminal 190. When the thermostat system 
is to be incorporated into a model used only for the control of heating, a 
jumper W1 is connected between terminal 190 and row K8. When, on the other 
hand, the system is to be used to control both heating and air 
conditioning, jumper W1 is removed and a jumper W2 is instead connected 
between terminal 190 and row K4. In the first alternative when the system 
is utilized only for the control of heating, only one of the two START 
buttons needs to be included. Preferably, however, they are paralleled by 
being placed side-by-side to form a physically larger START button. 
As will be apparent, columns J0 through J3 are individually connected 
through respective diodes D10 through D13 to the corresponding labeled 
output terminals of microcomputer 150 as shown in FIG. 4. Similarly, rows 
K1, K2, K4 and K8 are connected to the correspondingly labeled input 
terminals on microcomputer 150 also as shown in FIG. 4. 
The arrangement permits multiplexing of the involved outputs from 
microcomputer 150, while scanning of the inputs K1, K2, K4 and K8 is used 
to determine which button has been depressed. The arrangement within the 
microcomputer is such that only one of the designated outputs is enabled 
at any given instant, and only when one of those outputs is enabled are 
the K inputs scanned. Diodes D10-D13 serve to prevent any signals on the K 
input lines from being fed back into display driver 164. 
Keyboard 110 also preferably includes an overlying conductive shield 192 
that is connected through a terminal 170 back through the terminal of the 
same number in FIG. 2 so as to be coupled directly to the twenty-four volt 
alternating-current supply at terminal 120. However, shield 192 is not 
exposed to the user. It allows any discharge of static electricity to be 
dissipated harmlessly into the input supply transformer. Without shield 
192, static could discharge through the keyboard into microcomputer 150, 
possibly causing permanent damage. 
Display 112 includes display driver 164 and a display device 200. Display 
driver 164 as herein specifically implemented is a DS8872 integrated 
circuit chip as conventionally designated. Its input terminals as 
externally designated by the symbols J0 through J8 are connected to the 
correspondingly labeled output terminals of microcomputer 150 as shown in 
FIG. 4. As mentioned above, its pin 11 is returned to ground through 
resistor R32 and terminal 220 to the ground path depicted at the bottom of 
FIG. 4. Display driver 164 is basically a series of buffers that also 
function as inverters in the manner specifically illustrated. FIG. 5A 
depicts the typical circuitry of each of those buffer-inverters. Thus, 
each J input terminal of the driver is connected through a resistor 204 to 
the base of a transistor 206 the collector of which leads to a digit 
cathode in display device 200. The emitter of transistor 206 is returned 
to ground, and the base and emitter are shunted by an input resistor 208. 
Pin 22 of driver 164 is connected to Vcc through a terminal 129. 
As particularly implemented herein, display device 200 is a so-called 
display stick of a twelve-digit type, such as that under the commercial 
designation 5082-7445C. Counting from the left in FIG. 5, its fourth and 
sixth digits are not utilized, and its ninth digit actually is a colon 
while all of the others are conventional seven-segment arrays of 
light-emitting diodes, so as to be able to define either numbers or 
letters in the normal manner. It is intended that the first three digits 
from the left indicate whether in a heating or air cooling mode and 
temperature, such as H72 or A72. The fifth digit indicates the day of the 
week as arbitrarily assigned but later assumed herein to be a 
representation of Sunday as a "1" through the following Saturday as a "7". 
The remaining digits used present the time, such as "10:30A" for 
ten-thirty in the morning. 
The lower line of numbers on device 200 as drawn in FIG. 5 once again are 
the conventional pin numbers assigned by the manufacturer of the 
component. Immediately above the row of pin numbers is another row which 
sets forth either the segment anode letter or the digit cathode number. As 
usual, the segment anode letters indicate the terminals which need to be 
energized to select display segments within each unit of the display, and 
the digit cathode numbers refer to which display units within the overall 
device are to be energized. Hence, there are no connections to units four 
and six which, as indicated, are intended to remain unused. 
Accordingly, the seven different terminals assigned to segment 
determination are labeled "a" through "g" and are connected to receive 
that output information from the correspondingly-labeled output terminals 
on microcomputer 150 in FIG. 4. For selectively enabling the various 
cathodes, the various pins numbered 12 through 20 in driver 164 are 
individually connected appropriately to display device pin numbers 9, 10, 
12, 13, 14, 16, 17, 18 and 20, with driver pin 16 also being connected to 
device pin 19. There is no separate connection to the ninth display unit, 
the colon of that display being illuminated automatically whenever the 
last digit is displaying either an "A" or a "P". The decoding for the 
input lines "a" through "g" is determined within microcomputer 150. 
It will be recalled that, in the discussion of the switching system of FIG. 
2, an ultimate command-to-operate or enable signal is derived from the 
sub-system of FIG. 4 and delivered to the sub-system of FIG. 2 through a 
terminal 145. That command signal appears at an output J9 (terminal pin 2) 
of microcomputer 150 as shown in FIG. 4. To achieve almost instant 
triggering of TRIAC 123, while delaying its return to a non-conductive 
state for a minimum period following termination of the command signal at 
output terminal J9, the output is connected from the latter and fed 
through a network which includes the series combination of inverters 210 
and 211. The latter drives the base of a transistor Q2 operated in the 
emitter-follower mode, so as to provide an ultimate command signal from 
its emitter through terminal 145 to the junction between resistors R10 and 
R11 in FIG. 2. That same command signal also is fed through a current 
limiting resistor R39 and a terminal 214 to the decimal point segment 
terminal DP at pin 6 of display device 200. In operation, therefore, 
illumination of the decimal point informs the user that the thermostat is 
calling for heat. 
The collector of transistor Q2 is returned to internal supply voltage Vcc 
by terminal 129 to which terminal 129' also is connected. The 
aforementioned time delay is provided by a capacitor C9 shunted by a 
resistor R20 and returned from the input of comparator 210 to ground. 
Increased discharge of capacitor C9 is provided by the series combination 
of a diode D4 and a resistor R1 shunted between the input of inverter 210 
and the output of inverter 211. 
Microcomputer 150 is a conventional TMS1100 as commercially designated and 
which includes not only the integrated microcomputer circuitry but also 
has its own clock. That clock sets the rate at which the microcomputer 
executes the permanent program instructions in its read only memory (ROM). 
Accommodating the separation of the overall schematic representation, as 
separated between FIGS. 2 through 5 in accordance with available space on 
each sheet of the drawings, the internal positive operating potential Vcc 
is made available through a terminal 216 from FIG. 2. Analogously, the 
ground return from pin 4 of microcomputer 150, also labeled Vdd, is shown 
as connected by a terminal 218 to the sub-system of FIG. 2 and also by 
terminal 220 to the sub-system of FIG. 3. It may be noted that each output 
of microcomputer 150 typically is an emitter-coupled transistor 220a as 
shown in FIG. 4a. 
Setting the frequency of operation of the clock integrated within 
microcomputer 150 is a network consisting of a capacitor C5 coupled on one 
side to Vcc as at terminal 216 and from its other side through a resistor 
R27 and a potentiometer P3 to ground. The junction between capacitor C5 
and resistor R27 is connected to clock-oscillator pin terminals 18 and 19 
on microcomputer 150. 
Of course, the read only memory in microcomputer 150 must be permanently 
programmed or set up to appropriately receive information from and provide 
information to the different sub-systems involved and in accordance with 
the ultimate nature of the overall functions that are to be performed. 
While any two different programmers of the read only memory might end up 
with substantially different schemes for achieving the same ultimate 
result, a preferred loading program is set forth in FIGS. 27 through 56. 
Actually, the flow charts set forth in FIGS. 27 through 56 need little, if 
any, further explanation, because they are presented in the form of a 
series of successive instructions or statements that use language well 
known and sufficient for the person skilled in the art to understand and 
implement the loading of microcomputer 150. Standardized nomenclature is 
included throughout. Thus, RAM refers to the random access memory within 
microcomputer 150, ACC refers to accumulator, K and J relate back to FIG. 
4 and the respective inputs and outputs from microcomputer 150 and "F's" 
refers to flag sets or numbers. DEC refers to decrement, AIR refers to air 
conditioning control and HEAT refers to heating control. 
FIGS. 27 through 30 depict the overall "Start" routine, but, as indicated, 
involve correlation with a number of other routines and subroutines. For 
example, FIG. 29 has a step which calls for going to a "Flash-Help" 
routine. That, in turn, is presented in FIG. 31 and is a necessary start 
for the "Find Temperature" routine that begins also in FIG. 31. It will be 
noted that the "Find Temperature" routine is employed twice as a 
sub-routine just in FIG. 29. FIG. 32 indicates a "Go to Test" step which 
requires going back to FIG. 27. These are only examples of the many 
interrelationships which exist between the various routines and 
subroutines set forth in the many figures. Of course, many of the routines 
continue from one figure to the next by reason of space limitations on any 
given drawing sheet. In any case, the cross-references or transfers 
between the different main routines, as well as different subroutines, are 
clearly indicated in FIGS. 27-56. 
Included are a number of subroutines, such as the "Increment Temperature" 
subroutine in FIG. 31, the "Find Input Timing Pulse" subroutine in FIG. 
37, the "Compare Air to Heat" subroutine of FIG. 38, the "Verify 
Temperature" routine of FIG. 44, the "New Time" routine of FIG. 46, the 
"Temporary Override" routine of FIG. 46, the "Increment Time" subroutine 
of FIG. 47 and the "Display Timer" subroutine of FIG. 49. Others include 
the "DIGIN" subroutine of FIG. 46, the "AM/PM" subroutine of FIG. 52, the 
"Increment Pointer" subroutine of FIG. 51, the "Decrement Pointer" 
subroutine of FIG. 51, the "Full" routine of FIG. 52, the "Get Four Bytes 
of Data" subroutine of FIG. 53, the "Store Four Bytes of Data" subroutine 
of FIG. 54, the "Conversion F.degree. to C.degree." subroutine of FIG. 56 
and the "Conversion From C.degree. to F.degree." subroutine of FIG. 55. 
One central objective in programming the read only memory (ROM), of course, 
is the ultimate acceptance of data input from the user. That is primarily 
established by the "Input Data" routine which begins on FIG. 37 and 
continues through FIGS. 38-42 to FIG. 43. Data entry by the user involves 
the addressing, by means of keyboard 110, of the random access memory 
(RAM) within microcomputer 150. As indicated in the flow charts, the RAM 
also is used temporarily to store instruction and test data employed in 
the permanent programming of the ROM. It is the RAM, however, which must 
be addressed by the user in order to benefit from the ordinarily 
non-erasable data stored in the ROM. Another major objective in 
programming the ROM is to establish the different functions which monitor 
and govern operation of the various stages and, of course, which respond 
to the sensed temperature. 
After assembly into housing structure yet to be described in more detail 
and loaded with read only memory programming in accordance with the 
procedure outlined by FIGS. 27 through 56, the overall thermostat thus is 
ready for selective programming by the user. Of course, the ordinary user 
would never be able to program the read only memory in microcomputer 150 
in the manner necessary to achieve the desired results. Accordingly, the 
microcomputer itself and its permanent loading are selected to allow 
comparatively simple addressing of the thermostat by the user. Through 
keyboard 110, the user enters day, time and temperature information as the 
basic input data. As will be seen, certain other functions also are 
available. Those selections are displayed by device 200 and, if correct, 
the user then is able to store that information, so that it will govern 
operation of the thermostat. 
To this end, a control panel shown in FIG. 10 includes pushbuttons labeled 
essentially as previously described with regard to FIG. 5. As shown in 
FIG. 10, however, there is but a single START pushbutton area and no 
separate pushbutton with respect to air conditioning. This is the 
preferred arrangement when the thermostat is intended for use only in the 
control of heating and in the absence of air conditioning. For economy of 
parts procurement, however, keyboard 110 is in this case fabricated to 
include a separate pushbutton element for use when air conditioning also 
is to be controlled. As discussed in more detail in connection with FIG. 
25, all of the actual pushbutton contacts are disposed beneath a flexible 
insulative layer on which the labels are printed. There are, therefore, 
both START HEAT and START AIR button contacts located side-by-side beneath 
the single label START on a heat-only model, so that both may be depressed 
simultaneously. 
For such a version intended only to control heating, jumper W1 is connected 
and jumper W2 is not connected. At the same time, resistors R26 and R30 
and modules 138 and 138a or 138a' may be omitted. For a model intended to 
control both heating and air conditioning, on the other hand, those 
components are included and jumper W2 is connected instead of jumper W1. 
At the same time, separate START HEAT and START AIR labels preferably are 
used as specifically shown in FIG. 25. Those two labels individually 
overlie the respective button contacts mentioned above. 
As previously indicated, the differently-numbered pushbuttons of keyboard 
110 also carry abbreviations relative to the days of the week. As 
specifically shown in FIG. 10, pushbuttons "1" through "7" are denominated 
to indicate individually the respective days Sunday through Saturday. 
Pushbutton "8" is assigned a designation "M-F" to indicate Monday through 
Friday, pushbutton "9" is designated with "S/S" to indicate Saturday and 
Sunday and pushbutton "O" contains the designator "All". These different 
designations with respect to days of the week are intended to permit the 
user to enter a control program with respect to any specific day of the 
week, to apply a common program to any succession of five straight days 
such as Monday through Friday, to order a different manner of operation 
for days off such as Saturday and Sunday or to select a manner of 
operation applicable to all days of the week. 
Of course, the separation of Saturday and Sunday from Monday through Friday 
as here shown by way of example is in accordance with what has been the 
standard work week for a majority of the population. At the same time, 
however, this assignment is entirely arbitrary and the user may employ the 
sequence of numerals to reflect any choice as to the beginning of a weekly 
cycle; that is, the pushbutton which bears numeral one could be used to 
designate a Wednesday, in which case the pushbutton bearing numeral eight 
would apply to the days Thursday through Monday and the pushbutton 
enumerated "9" would end up automatically applying to Tuesday and 
Wednesday. 
As presented in FIGS. 9 and 14, the pushbuttons of keyboard 110 are exposed 
through openings in a bezel 220 mounted on a housing 222. Bezel 220 
surrounds the upper margin of a well 224 in which battery 152 is to be 
located and which normally is covered by a plate 226 on the outer surface 
of which is printed a series of basic user instructions as shown better in 
FIG. 26. The content of those instructions will be appreciated more fully 
after consideration of the following description of user operation. By 
observation of the small rectangles which correspond to different ones of 
the pushbuttons shown in FIG. 10, it will be seen that these instructions 
present a visual cross-reference. Of course, the labeling as to each 
different instruction is self-evident. Nevertheless, the instructions set 
forth on panel 226 pertain only to the usual set of input entries required 
from the user. Instruction as to other possible selected programming is to 
be included in an associated instruction manual. 
Bezel 220 also accommodates the light output from display device 200 
situated relative to appropriate indication of "TEMP", "DAY" and "TIME". 
This visual display will indicate those informational values as they are 
being programmed into the unit as well as indicate the same information at 
any time that the REVIEW pushbutton is depressed. The differently-numbered 
keys are used to relate to the days of the week as arbitrarily selected 
and assumed herein to begin with Sunday as well as to allow the input of 
desired temperature and time information. Overlying all of bezel 220, 
display device 200, keyboard 110 and plate 226 is a transparent cover 228 
hinged to swing to an open position, so as to allow access to the 
keyboard. 
Depression of the START button always prepares the unit to receive new 
programming information and also functions to activate display device 200 
for a period of time, in the present case of about thirty seconds from the 
last depression of a key that causes microcomputer 150 to set up, and to 
enter or store data effectively received from or supplied to the display, 
excepting error messages. The AM/PM button is used to select as between 
those respective portions of the time of day; as herein embodied, each 
activation of the unit by use of the START button results in operation of 
the unit in the AM mode which will be indicated by the letter A at the 
right-most digit of the display. However, each depression thereafter of 
the AM/PM button will result in a switching as between AM and PM, and this 
button can be depressed to effect that change at any time. The CLEAR 
button is employed to erase information temporarily fed into the unit 
through the other pushbuttons but determined, by means of display device 
200, to be incorrect; it also is used to erase any set of instructions 
when used in association with the REVIEW button as hereinafter described. 
The STORE button instructs the unit to retain information "punched in" 
through use of the other buttons. That is, those other buttons are used to 
enter information which is observed on display device 200 and, when that 
observation reveals correct entry, the STORE button then must be depressed 
in order actually to load microcomputer 150 with that information. 
The REVIEW button activates display device 200 and allows the user to 
determine both current environmental values and also to check the status 
of instructions that previously have been placed into the unit. On the 
first depression of the REVIEW key, it indicates current temperature, day 
and time. When thereafter depressed repeatedly, it enables the successive 
display on device 200 of the various sets of programmed instructions. As 
will be discussed further below, cover 228 is so formed and mounted that, 
when lightly depressed inwardly, it activates the REVIEW pushbutton. 
User programming will depend, of course, upon the user's personal time 
schedule. The following discussion will assume that the controller is 
installed in a residence, that activity within the residence is during the 
daylight hours with sleep at night, that household activity begins later 
on the weekends and that there are one or more unique times when the 
normal repetitive routine is to be excepted. 
It should be noted that the user-programmable information desirably stored 
within the thermostat automatically is erased from its random access 
memory at any time that supply power, by way of battery 152 and by way of 
input terminal 120, is removed. Whenever that has occurred and power 
thereafter is restored, microcomputer 150, by reason of its permanently 
stored program, will cause device 200 to flash the signal "HELP". That 
informs the user that the accessible memory is blank but ready for again 
being programmed. 
As an overview of user programming, START is depressed at the beginning; 
this activates the unit, including display device 200. Next, the time 
clock is set. This is achieved by entering the temperature of zero-zero 
for Celsius or zero-one for Fahrenheit followed by the day of the week and 
the time of the day. Temperature control instructions are then programmed 
into the unit, subject to always following a sequence of 
temperature/day/time of day. A lighted bar appears at the appropriate 
location on display device 200 to make each sequence easier to follow by 
reminding the user what information is next to be entered. When the 
display provided by device 200 indicates that the desired information has 
been supplied, the STORE button is depressed to cause that total 
instruction to be placed within the memory of the microcomputer. The same 
procedure is repeated for each different set of instructions with respect 
to different days and times until all such information has been stored. 
As a more detailed example, assume the selection of a program which will 
call for weekday heating to a level of seventy degrees (70.degree.) F. 
beginning at six-thirty (6:30) AM, setting that level back to sixty 
degrees (60.degree.) at eight (8:00) AM and then rewarming to seventy 
degrees (70.degree.) beginning at five (5:00) PM with a final set back to 
sixty degrees (60.degree.) at eleven (11:00) PM. On the other hand, it is 
desired to begin heating to seventy degrees (70.degree.) on Saturday and 
Sunday at nine (9:00) AM, later reducing the temperature to sixty-five 
degrees (65.degree.) at one (1:00) PM in recognition of increased personal 
activity, returning to seventy degrees (70.degree.) beginning at five 
(5:00) PM and finally setting to a night temperature of sixty degrees 
(60.degree.) at eleven-thirty (11:30) PM. 
In achievement of the foregoing, operation once again is begun by setting 
the clock and instructing the unit to keep track of current temperature, 
day and time. To do this, depress START and then "zero-one", since the 
temperature is to be in Fahrenheit. Next is to depress the appropriate 
number for the current day of the week, as assigned on a one-through-seven 
basis, and not the date of the month. Immediately thereafter, the suitable 
buttons are depressed in order to enter the digits that represent current 
time along with the designation AM/PM if it is afternoon or evening. 
Finally, the STORE pushbutton is depressed, after which REVIEW may be 
depressed at any time in order to obtain a readout of current temperature, 
day and time. 
Turning next to the temperature-control instructions for the assumed 
example, the sequence of key depression is 
START--Seven-Zero--Eight--Six-Three-Zero--STORE in order to cause heating 
of the house to seventy degrees (70.degree.) on Monday through Friday at 
six-thrity (6:30) AM. In itself, the colon is already there, so it does 
not have to be entered. Also, the AM is already present as mentioned 
previously with regard to the condition of the unit on initial start up. 
In order next to instruct the unit to set back to sixty degrees 
(60.degree.) on Monday through Friday at eight (8:00) AM, the sequence is 
START--Six-Zero--Eight--Eight-Zero-Zero--STORE. For returning to seventy 
degrees (70.degree.) on Monday through Friday beginning at five (5:00) PM, 
the user must follow the routine of 
START--Seven-Zero--Eight--Five-Zero-Zero--AM/PM--Store. Note that the 
AM/PM button must be depressed in order to change that function that had 
been automatically preset to AM upon initiation and, if changed, is 
automatically reset to AM upon each depression of START. Again for the 
late evening, the order of actuation is 
START--Six-Zero--Eight--One-One-Zero-Zero--PM--STORE. 
As to all of the sequences thus described, it is to be noted that the 
entering of each sequence is displayed by device 200 as it is keyed. That 
means that the entry of each individual instruction can be checked for 
accuracy before going to the next instruction. Should a mistake be 
observed at that point, it is only necessary to depress the CLEAR button 
and begin anew with respect to the particular instruction at hand. After 
pressing STORE at the end of a full temperature-day-time sequence, the 
entire stored sequence is displayed to allow one further visual check. If 
an error is noted, depression of CLEAR erases the entire sequence after 
which it can be re-entered correctly. 
Continuing with the example, the next sequence is for heating the house to 
seventy degrees (70.degree.) on Saturday and Sunday beginning at nine 
(9:00) AM. For this, the operation is 
START--Seven-Zero--Nine--Nine-Zero-Zero--STORE. Of course, the first 
"nine" in that sequence refers to the Saturday/Sunday mode or other 
arbitrary "weekend" period as previously discussed. 
In order to set back the heat to sixty degrees (60.degree.) during the 
weekend at one (1:00) PM, the next instruction is 
START--Six-Zero--Nine--One-Zero-Zero--AM/PM--STORE. For returning to 
seventy (70.degree.) degrees again on the weekend at five (5:00) PM, the 
sequence is START--Seven-Zero--Nine--Five-Zero-Zero---AM/PM--STORE. 
Finally, the late night condition is reached by the routine of 
START--Six-Zero--Nine--One-One-Three-Zero--AM/PM--STORE. 
In accordance with the foregoing, a set of instructions has been entered so 
as to cover all days of the week. Nevertheless, the system will also 
handle additional instructions for more specific time periods. Assume a 
regularly scheduled absence from the residence on each Tuesday night 
between seven (7:00) and nine (9:00) PM. To conserve energy during that 
absence, additional instructions to be entered could be 
START--Six-Zero--Three--Seven-Zero-Zero--AM/PM--STORE, and 
START--Seven-Zero--Three--Nine-Zero-Zero--AM/PM--STORE. 
The microcomputer is programmed permanently to pay attention always to the 
most specific set of instructions within any given time span. Since 
"Tuesday" (represented by the "three" in the example just given) is more 
specific than the previously-entered "Monday through Friday" instruction, 
the latter information is superceded upon the entry of the special Tuesday 
night program. Similarly, the most specific set of instructions are 
followed even when they are redundant or "conflicting" by calling for the 
same time. Assume in the last example no return to the residence on 
Tuesday from morning until nine (9:00) PM. To overcome the normal Monday 
through Friday heating to seventy (70.degree.) degrees at five (5:00) PM, 
the first additional instruction would be 
START--Six-Zero--Three--Five-Zero-Zero--AM/PM--STORE. That would then be 
followed by the second additional Tuesday instruction as before. Thus, the 
more specific Tuesday-only instruction governs, even though a point of 
time is the same as in the more general Monday-Friday instruction set. 
It may be noted that, as particularly embodied herein, the thermostat 
accepts the instructions only with respect to the hours and the half 
hours. Should a time other than that be entered, microcomputer 150 
automatically will correct to the appropriate half-hour format. 
As indicated on panel 226, also contemplated are the provisions for either 
temporary override or what is termed vacation override. Use of either of 
those alternative operations enables the user to supercede the regular 
program while yet retaining that in the memory for subsequent use as 
already programmed. 
Temporary override is initiated simply by the sequence of START, input of 
desired temperature numbers and STORE. This automatically effects control 
to the newly selected temperature in a manner which is maintained until 
the next regularly scheduled set of instructions is called for. For 
example, assume there is a desire on Wednesday afternoon to increase the 
temperature temporarily, that being a time when, in accordance with the 
earlier example, the temperature was to be controlled to sixty 
(60.degree.) degrees until five (5:00) PM. In order, then, to temporarily 
increase the temperature to seventy-two (72.degree.) degrees, all that is 
necessary is to successively depress the sequence START--Seven-Two--STORE. 
The temperature will be controlled to seventy-two (72.degree.) degrees 
thereafter until five (5:00) PM when it will be reset automatically to 
seventy (70.degree.) degrees in accordance with the regularly programmed 
instructions. 
The vacation override feature involves what might be considered a 
"temporary" override but for a period of time longer than the end of the 
regular programming interval being overridden, including periods that may 
extend for a number of days. For this purpose, a special code is inserted 
into the program. This is achieved by the sequence START--desired 
temperature--Zero-Zero-Zero-Zero-Zero--STORE. The temperature thereby 
entered will be retained until whenever the user returns and once again 
pushes the REVIEW button. As an example, assume a long weekend during 
which it is wished to maintain the heat at fifty-five (55.degree.) 
degrees. The instruction would be 
START--Five-Five--Zero-Zero-Zero-Zero-Zero--STORE. Upon return, a mere 
push of the REVIEW button restores the unit to the regular program. 
It is to be noted that the latter will not necessarily turn on heat (or air 
conditioning). It simply causes the unit to be directed to go back to the 
regular routine as initially programmed. Should that pose a problem, such 
as not causing heat to be produced immediately upon return, the temporary 
override program previously described may be utilized to substitute for 
the regular program. 
At any time, the temperature display and all programmed instructions may be 
expressed either in Fahrenheit or Celsius. If Celsius is desired, it is 
only necessary to follow the sequence START--Zero-Zero--STORE. Should 
Fahrenheit be desired, the middle step of that sequence is, instead, 
"Zero-One". 
It is to be remembered that the CLEAR pushbutton is utilized for the 
purpose of correction or change. The correction of data just entered or 
just stored has already been described. Changes to already stored regular 
programs are made by first repeatedly pushing REVIEW the number of times 
necessary to reach the desired step as then visualized upon display device 
200. At that point, the depression of CLEAR will entirely erase the 
original instruction from the memory. The user may then re-enter a new 
instruction, if desired. It should be noted that the order of entry of 
sets of instructions is not important. 
Also included is an error system which serves both to indicate a weak 
battery condition and also to visually demonstrate when it has been 
attempted to supply incorrect information. As specifically embodied 
herein, four different error codes are included for visual display on 
device 200 of a heat-only model. When air conditioning also is controlled, 
there are two additional error codes. A mistake of entry results in the 
flashing of an error code on device 200; under that condition, the unit 
will not accept the mistaken information. It is simply ignored, and proper 
information then is entered in place of that which was ignored. 
When an entry is made that is outside the acceptable design temperature 
range, (50.degree.-89.degree. F.) or (10.degree.-29.degree. C.) in the 
instant embodiment, the display "Err1" will be visually produced. Also, 
the embodied unit is programmed so that, when first energized, it is 
automatically set to provide indication in Celsius. Any attempt at that 
point to enter a Fahrenheit temperature will result in the display of 
"Err1". To avoid that error, the unit must first be programmed for 
Fahrenheit by using the zero-one code as above described. Again, should an 
improper entry be attempted, the unit will not accept it and the correct 
entry can then immediately be offered. 
Should an "Err2" appear, that will mean that an improper day code was 
employed to originally set the time clock. This indicates that one of 
pushbuttons "eight", "nine" or "zero" had been depressed instead of a 
pushbutton assigned to a specific day. The display of "Err3" reveals that 
an improper time was used in setting the clock. That will occur, for 
example, if the user attempts to enter a universal time such as the number 
"eighteen hundred". As embodied, the system contemplates use of time 
information represented only in AM and PM modes. If desired, however, the 
ROM program could be changed to accommodate time on the basis of a 
twenty-four hour format. In that case, of course, the AM/PM pushbutton no 
longer would be needed. When an instruction is entered that results in a 
temperature conflict as between heating and air conditioning, an "Err4" or 
"Err5" will appear. Besides giving that message, the thermostat 
automatically resolves that conflict so that both heating and air 
conditioning cannot occur simultaneously. 
Finally, and in connection with battery monitor 102, a display of the 
signal "Err7" indicates that the battery is becoming weak. This warning 
will be indicated upon depression of either a START or a REVIEW pushbutton 
for the first time. Upon quickly again depressing that key, the error code 
"Err7" will disappear, and the unit can again be normally operated until 
there is such additional degree of weakening of the battery as to prevent 
operation in the battery-supplied mode, normal functioning always being 
available so long as the input alternating-current is supplied to terminal 
120. 
It is significant to note that one purpose of including battery 152 is to 
preserve user-programmed information in the event of an external power 
failure during normal operation. Of course, the battery should be replaced 
any time that the "Err7" signal appears. Battery 152 also serves to enable 
the unit to be disengaged from its mounting and, for example, to be 
carried from room to room to check upon different temperature variations 
or to be placed on a table for convenience during user programming. 
As specifically embodied in accordance with the foregoing description, it 
may be noted that there are twenty-three possible set points to any 
integer termperature from fifty degrees (50.degree.) F. to eighty-nine 
degrees (89.degree.) F. Each set point controls the temperature for a 
particular day only, a group of days or every day. Display device 200 
automatically is disabled after a preselected observation period, provided 
that the keyboard has not been used during that interval in a manner to 
effect a data operation. In general, this exemplified system is designed 
to maintain a temperature accuracy to within one degree Fahrenheit over 
the operating range. 
In a system which utilizes a pilot, such as a furnace fueled with gas or 
oil, it is possible to manipulate a conventional electro-mechanical 
thermostat in a manner to literally blow out the pilot. This can occur if 
the gas valve is opened only for about one to two seconds and is then 
closed. That causes the flow of gas to be turned off at about the same 
time that ignition occurs, and the resulting explosion or implosion may 
extinguish the pilot. To avoid that possibility, and thus for the purpose 
of safety, the values of capacitor C9 and resistor R20 are selected so 
that, together with inverters 210 and 211, there is a time delay of about 
four and one-half (4.5) seconds after opening of the gas valve before it 
can be closed. 
As already indicated, the thermostat is contained primarily within a 
housing 222. With reference to FIGS. 9-14, the overall assembly includes a 
mounting plate 240, a lower housing portion or base 242, a printed circuit 
board 244, an upper housing portion or case 246, battery compartment cover 
or plate 226 and transparent cover 228. 
Mounting plate 240 is intended to be affixed to the wall of a room at the 
location on the wall from which the wires that lead to the heating and/or 
air conditioning systems emerge. Of course, any existing thermostat 
assembly is first removed. After feeding the wires through an opening in 
plate 240, the plate is secured to an electrical junction box, as provided 
in the wall and of typically appropriate size, or directly to the wall by 
means of suitable fasteners. In a manner to be described further, the 
wires are connected to respective different resilient contact members on 
plate 240. Also included on plate 240 are fastening parts that mate with 
other fastening parts on the bottom of base 242 in a manner to permit 
housing 222 thereafter to be mounted upon plate 240 by being simply 
slipped into place. At the same time, the aforementioned contact members 
are arranged in association with other contacts in housing 222 so as 
automatically to complete electrical connection to the thermostat. As 
desired at any time thereafter, housing 222 may be slipped from its 
mounting upon plate 240 and carried elsewhere. During that time of 
removal, the thermostat continues to operate from its self-contained 
battery 152. The thermostat subsequently may be remounted upon plate 240 
as easily as before. 
FIG. 11 is a view of the side of mounting plate 240 that, when installed, 
faces the wall. Also visible in FIG. 11 is the bottom of base 242 as 
mounted in place upon plate 240. To be seen also are the heads of two of a 
total of four mounting screws 250 which project through base 242 into 
engagement over a correspondingly aligned plurality of hollow posts 252 
which depend downwardly from the top of case 246 for completing the 
assembly of housing 222 (FIGS. 17A and 18). 
Mounting plate 240 is molded from an electrically-insulative plastic 
material and shaped to include a matrix of reinforcing ribs 254 that lend 
rigidity. A first pair of elongated holes 256 and 257 are located 
centrally near respective opposing margins, and another space-opposed pair 
of elongated openings 258 and 259 are respectively located near the other 
pair of opposed side margins. The nominal distance between each 
space-opposed pair of openings 256-259 is the same as that between the 
threaded mounting holes provided in a standard 2.times.4 inch electrical 
junction box as often installed in the wall of a building for the mounting 
of a thermostat. Thus, the two pairs of these holes permit mounting to 
such a box whether it is oriented horizontally or vertically. Moreover, 
the two of the holes in each space-opposed pair are elongated in 
respective directions at right angles to one another to accommodate slight 
variations as among different junction boxes and also to allow the 
mounting of plate 240 in a level position even though the junction box is 
a little tilted as installed in the wall. As indicated above, selected 
ones of holes 256-259 may, in the alternative, be used for the receipt of 
fasteners of some other kind used for the purpose of securing plate 240 to 
the wall in a different manner. On the other side of plate 240, as may be 
seen in FIG. 15, the reinforcing ribbing on that surface is formed as at 
260, for example, to generally encircle each of holes 256-259, and the 
surface is depressed within each such encirclement so that a well is 
defined to accommodate the receipt of the head of a screw or other wall 
fastener that will thereby not interfere with the mounting of housing 222 
and result in a thinner profile of the mounted thermostat. 
Projecting outwardly from the lateral margins of plate 240, near its bottom 
margin as mounted, are respective lugs 262 and 263. Also projecting from 
those lateral margins, but near the top of plate 240 as installed, are 
respective ones of another pair of lugs 264 and 265. As may be seen in 
FIG. 15A, each of lugs 262 and 263 is shaped to define a finger 266 on 
which is formed a notch 268 from which the finger narrows in the direction 
toward the open end of the lug. Lugs 264 and 265 have the same shape 
except for the omission of notch 268. 
Turning for a moment to FIG. 16 for a look at the bottom surface of base 
242, it will be observed to have a space-opposed pair of lateral margin 
areas 270 and 272 between which is recessed a panel 273 that constitutes 
most of the bottom surface. Projecting toward one another from areas 270 
and 272 are a pair of respective ears 274 and 275 located in a position 
below the middle of panel 273 as viewed in FIG. 16. Disposed upwardly 
therefrom and projecting toward one another from margins 270 and 272 are 
another pair of ears 276 and 277. With reference to FIG. 16A, it will be 
observed that ear 275 is in the form of a finger 276 shaped to include a 
notch 278 from which the finger narrows toward the open end of the ear. 
Ear 276 is formed in the equivalent manner. Ears 276 and 277 are of 
essentially the same shape as ear 275 except for the omission of notch 
278. 
The different ones of lugs 262-265 are located in a pattern which 
corresponds with a pattern of respective ears 274-277. Lugs 262-265 may be 
defined as slideways and ears 274-277 as guideways. To mount housing 222 
upon mounting plate 240, therefore, it is only necessary to align the 
various lugs and ears and slide them together into mutual 
interrelationship. This is the same as if FIG. 16A were moved generally to 
the left into FIG. 15A until finger 276 was fully beneath the full length 
of finger 266. Fingers 266 and and 276, and their corresponding 
equivalents, are slightly resilient as a result of which the different 
notches 268 and 278 become sufficiently interengaged to seat housing 222 
in proper position on plate 240, while yet permitting rather easy 
disengagement when desired. Note that FIG. 16A has been rolled over 
one-hundred-eighty degrees with respect to what normally would be 
indicated by the section line 16A--16A in FIG. 16. 
Somewhat centrally disposed in mounting plate 240 is an opening 280 spaced 
below another opening 282 slightly beneath which, as viewed in FIG. 11, is 
a smaller tab 283. During installation of mounting plate 240 on the wall, 
the wiring preferably is led through opening 280 and then tucked under tab 
283 (as viewed in FIG. 15) before being connected to switch contacts 
mounted upon plate 240. If the wires are too short, they may be led 
directly through opening 282. 
Mounted on and projecting downwardly below the bottom margin of mounting 
plate 240 as installed is the free end 286 of a switch handle in the form 
of a lever 288 that has a pivot pin 290 captivated in a bearing hole 292, 
formed through plate 240, by a lip 294 which overlies a stub 296 
projecting radially outward from pin 290 (see both FIGS. 11 and 15). Stub 
296 swings within an annular segment 298 opening outwardly from the upper 
side of bearing hole 292. Lip 294 only partially overlies segment 298 so 
as to leave a small gap 300 through which stub 296 may be inserted into 
the segmental region beneath the lip during assembly. 
Lever 288 has been removed in FIG. 15 but may be seen as mounted in FIG. 
14. Light finger pressure against its preferably knurled free end 286 is 
sufficient to swing lever 288 about pin 290 between space-opposed limits 
302 and 304 as defined by reinforcing ribs on the surface of plate 240 
visible in FIG. 15 and as seen in FIG. 14. 
Also formed through mounting plate 240 are a first series of four 
successively and laterally spaced like openings 306 and a fifth opening 
308 of the same shape spaced beyond that series and displaced slightly in 
a downward direction as viewed in FIG. 11. Spaced respectively just below 
each of all of those openings are another series of four openings 310 
followed by a fifth opening 312 beneath opening 308. The space between 
each upper and lower opening serves as a reinforcing rib 313 for this 
region of plate 240 which otherwise might be excessively weakened by the 
provision of so many openings in a limited area; rib 313 also has another 
purpose to be described below. 
Viewable in FIG. 11 through all of the openings just described are the legs 
of a plurality of resilient contacts 314, 315, 316, 317 and 318. Turning 
to FIG. 15, it will be observed that resilient spring contacts 314 and 315 
have been removed to permit a view of what lies beneath. Upstanding from 
the surface of plate 240 presented in FIG. 15 are a series of 
vertically-oriented rubs 320 each successive pair of which is aligned with 
opposing sides of the different ones of openings 306, 308, 310 and 312. 
Extending laterally across all of ribs 320 is a reinforcing rib 322. 
Toward the upper end of ribs 320 and respectively spanning the spaces 
therebetween are a series of webs 324 each of which includes an upwardly 
opening slot 326 which, as shown, diverges apart at its upper end portion. 
As viewed in FIG. 15, the bottom surfaces of rib 322 and webs 324 are 
aligned at slightly above the level of the main surface 328 of mounting 
plate 240 which extends between ribs 320. At the same time, the top 
surface of rib 313, as viewed in FIG. 15, is aligned at that level. 
Resilient spring contact 318 is shown in FIG. 19. It is formed as a 
spring-tempered strip of an electrically-conductive material such as a 
phosphor-bronze alloy and includes a leg 330 which merges into a 
smoothly-curved re-entrant bend 332. Beyond bend 332, the strip continues 
as a finger 334 bent away from leg 330 at its upper end, bent back toward 
leg 330 at an intermediate crease 336 and then once again bent slightly 
away from leg 330 at the beginning of its free end portion 338. Starting 
at crease 336 and continuing through its free end portion 338, finger 334 
is necked down to a narrower width. 
Near the lower end of leg 330, the strip is deformed over a small circular 
area to form a button 340 which faces finger portion 338. Intermediate the 
length of leg 330 is a cutout 342 shaped to leave a narrow projection 344 
located centrally within cutout 342 and the free end of which faces bend 
332. Another cutout 346 is formed centrally around the circumference of 
bend 332 and in a manner to leave a stub 348 that projects toward leg 330 
with its free end spaced but a short distance therefrom when the contact 
is in its normal unflexed condition as shown in FIG. 19. Also as a result 
of the formation of cutout 342, an ear 350 is bent upwardly from leg 330 
so as to project toward leg 334 a distance insufficient to interfere with 
the bending of finger 334 toward leg 330 an amount to move portion 338 
against button 340. 
For convenience, contacts 314-317 are identical to contact 318, although, 
as will become apparent, button 340 is superfluous on contacts 315 and 
316. The width of the strip from which the resilient contacts are formed 
is selected so that width of leg 330 and bend 332 is only very slightly 
less than the spacing between each pair of ribs 320. The latter, together 
with cross ribs 313 and 322 as well as web 324, define a channel within 
which the leg 330 of each contact is snugly received and seated. As each 
leg 330 is inserted into its channel, its free end passes over cross rib 
313, then under cross rib 322 and finally into a position disposed in a 
very shallow channel 352 defined in surface 328 of plate 340. Although 
thin, the finite thickness of leg 330 is sufficient that the leg has to 
curve slightly over rib 313 which ends up being aligned near the bottom of 
cutout 342. As a result, the free end of projection 344 is deflected 
slightly toward finger 334, so as to become seated against the 
downwardly-facing end surface of web 324 as viewed in FIG. 11. Once 
mounted, therefore, each contact is constrained to remain in place during 
connection of a wire to it and also during mounting and dismounting of 
housing 222 from plate 240. 
After installation of mounting plate 240 on the wall, the end portion of 
each wire is stripped of insulation for a short distance and the bared 
portion is inserted through cutout 346 in bend 332 and under stub 348 
until the end of the wire abuts ear 350. Even in the unflexed condition of 
finger 334, the spacing between the free end of stub 348 and leg 330 is 
sufficiently narrow that the bared wire end portion is gripped. As finger 
344 subsequently is deflected toward leg 330 upon mounting of housing 322 
to plate 340, that gripping pressure is further increased. 
It will be seen in FIG. 14 that a pair of arms 354 and 356 project 
generally outward from respective opposing sides of the upper end of lever 
288. Affixed on the underside of those arms is an outwardly-facing 
generally C-shaped sheet of resilient conductive material the respective 
end portions of which define contact areas 358 and 360. 
Area 358 is so shaped that it makes wiping connection with button 340 of 
contact 318 throughout the range of swing of lever 288. Moreover, area 358 
is also shaped and so disposed that, when lever 288 is swung toward its 
limit 302, area 358 comes into wiping connection over button 340 of 
contact 317. On the other hand, the swinging of lever 288 toward its 
opposite limit 304 serves to bring area 360 into wiping contact over 
button 340 of contact 314. As already mentioned, the mounting of housing 
222 upon plate 340 results in flexural bending of fingers 334 toward the 
corresponding legs 330. However, the free end portion 338 of the finger 
334 of each of contacts 314, 317 and 318 is shaped so that at least those 
free end portions on contacts 314 and 317 are always clear of the 
respective ones of contact areas 358 and 360, so as not to interfere with 
movement of the latter into and out of connection with the corresponding 
buttons. 
Although it may be affixed in any suitable manner, the sheet which forms 
contact areas 358 and 360 is in this case staked onto mounting pins (not 
shown) on the underside of lever 288 as viewed in FIG. 14. During movement 
of the lever, the ends of those pins ride within shallow channels 362 and 
364 (FIG. 15) defined in surface 328 of plate 240. Because legs 330 are 
seated into channels 352, contact areas 358 and 360 ride over the very 
lower end of the corresponding legs 330 as they approach rounded buttons 
340. 
Referring back to FIG. 2, it may now be appreciated that lever 288 serves 
as the switch for manually controlling the functions associated with the 
circulating fan or blower of an air conditioner. That is, contact 318 is 
terminal 140 and areas 358 and 360 constitute switch element 142. Contact 
317 corresponds to terminal 141, while contact 314 corresponds to terminal 
139. 
Returning to FIG. 16, a generally-rectangular opening 366 is formed through 
panel 273 in a position to allow the central portion of the fingers 334 of 
each of contacts 314-317 to project therethrough when housing 222 is 
mounted on plate 240. At one side of opening 366, and recessed into the 
surface of panel 273 as viewed in FIG. 16, is a shelf 368. Shelf 368 is so 
positioned that, when housing 222 is mounted upon plate 240, contact 318 
is aligned over the shelf. Because housing 222 is formed of a molded 
plastic which is an electrical insulator, this serves to isolate contact 
318 from electrical components within housing 222, while at the same time 
ensuring that the finger 334 of contact 318 is depressed so as to increase 
the gripping pressure of that contact upon its connected wire end. The 
upper and lower edge margins 370 and 372 of opening 366 are beveled away 
from the opening so as to assist the creases 336 of fingers 334 in gliding 
into and out of position as housing 222 is mounted and dismounted from 
plate 240. 
Formed through panel 273 at one corner of opening 366 is a circular hole 
374 of a diameter sufficient to permit the insertion of a screw driver for 
a purpose later to be described. Centrally located in the upper portion of 
panel 273, as viewed in FIG. 16, is another somewhat large and vertically 
elongated opening 376. To facilitate mounting of housing 222 on plate 240, 
the thickness of plate 240 is tapered so as to become thinner in the 
direction from lugs 262 and 263 toward lugs 264 and 265. That taper can be 
seen in FIG. 14. To allow an adequate recess for the head of a screw 
inserted through hole 256, its surrounding rib 377 projects above the 
level of the ribs 260 that encircle the other mounting holes. Opening 376 
accommodates rib 377. Moreover, the side walls of opening 376 tend to 
guide rib 377 during mounting of housing 222, so as to align ears 274-277 
properly with lugs 262-265. 
Also visible in FIG. 16 are a plurality of openings 378 through which 
screws 250 are inserted to enable engagement within the correspondingly 
positioned hollow posts 252 formed in case 246. Each of openings 378 is 
surrounded by a boss which defines a seat so that the flat head of each 
screw 250 is out of the path of the bottom of housing 222 during mounting 
and dismounting. 
As may be observed in FIG. 14, the other side of each of openings 378 is 
surrounded by a boss 380 of an internal diameter sufficient to receive and 
seat the very lower end of each of the corresponding ones of hollow posts 
252 and thereby matingly align case 246 with base 242. Also projecting 
upwardly from base 242 immediately on the inside, and distributed around 
an upwardly facing rim 381 of the base, are a plurality of upwardly 
projecting guides 382 over which are fitted corresponding portions of the 
lower margin of the skirt 284 of case 246. 
FIGS. 17, 17A and 18 are views of case 246 as stripped of associated parts 
shown in other views and some of which have already been mentioned. For 
this discussion of case 246, it will be assumed that the case is in an 
upright position as if the free margin of its skirt 284 were placed 
against the wall. A control panel area 390 occupies approximately the 
upper two-thirds of case 246 and is tilted so that its upper margin is 
spaced slightly to the rear of its lower margin. Continuing downwardly 
below control portion 390, as it slopes generally to the rear before 
merging into skirt 284, is a lower panel 392. 
Surrounding control portion 390 is an upstanding rim 394 which is 
continuous except for a gap 396 formed centrally in its upper leg. 
Immediately inside rim 394 throughout the extent of the latter, so as also 
to include gap 396, is a shelf 398 upon which bezel 220 is supported as 
shown in FIGS. 10 and 14. Depressed further to the rear from shelf 398, 
and around both sides and across the top of battery compartment 224, is a 
further shelf 400 upon which cover plate 226 is to be mounted as shown in 
FIG. 10. 
Battery compartment 224 is defined by a lower wall 402 (FIG. 17A), which 
depends rearwardly from near the upper margin of sloping panel 392, and an 
upper wall 404 that slopes rearwardly and downwardly from the upper margin 
of shelf 400 and merges into a ledge 406 which projects toward wall 402. 
An opening 408 is located intermediate the width of wall 404 and continues 
a short distance into ledge 406. Near the lower right-hand corner of ledge 
406, as viewed in FIG. 17, is a small slit 410 through which the leads to 
battery 152 are fed when the battery is installed within compartment 224. 
Battery cover 226, with the decal 412 of FIG. 26 removed, is shown in FIG. 
24. In FIG. 10, decal 412 is mounted in place upon the outer surface 414 
of cover plate 226 that has a rim 416 which surrounds that surface except 
for a gap 418 in the middle of the top margin. Decal 412 is coated with a 
self-sticking adhesive on its undersurface so as to secure itself to 
surface area 414 of cover 226 during assembly. Along the lower margin of 
cover 226 and projecting away therefrom is an inwardly-displaced lip 420. 
Projecting below surface 414 at the lower edge of an opening 421 therein 
is a tongue 422 having a catch 424. To install cover 226, lip 420 is 
tucked behind shelf 398 at the lower margin of battery compartment 224 
and, as cover 226 is pushed into place, catch 424 slides down sloping wall 
404 until it snaps into opening 408 aligned therewith and latches against 
the upper margin of that opening. The engaging face of catch 424 is 
slightly canted so that, upon slipping a fingernail into gap 418 and under 
surface 414, cover 226 is easily pulled open to permit access to the 
battery. 
Spaced above battery compartment 226 is an opening 426 behind which display 
device 200 is to be mounted. Recessed below shelf 398 and surrounding the 
top and both sides of opening 426 is a further shelf 428 upon which a lens 
430 (FIG. 10), shaped to fit snugly within the outline of shelf 398, is 
mounted. Lens 430 is transparent but preferably of the same color as the 
light emitted from display device 200 so as to improve contrast of the 
displayed numbers and letters in the presence of ambient light reflection 
from the lens. 
The legend "TEMP DAY TIME", as shown in FIG. 10, is printed in contrasting 
color across the upper portion of lens 430 and is located so as to appear 
over the illuminated digits displayed. Display device 200 is shown in FIG. 
23A and will be observed to be of generally rectangular shape and 
comparatively thin. It features a row of lenses 431a behind the operative 
ones of which are disposed light-emitting diodes of the seven-segment type 
as indicated in FIG. 5 (except for the colon). A narrow ledge 431b is 
formed on the lower margin along one side of the row of lenses, and a 
wider ledge 431c is provided along the opposite lower margin. A row of pin 
terminals 431d, corresponding to pin terminals 1-20 shown in FIG. 5, are 
disposed in ledge 431c. 
Along the top and down both sides, as seen in FIG. 18, opening 426 
continues into a partial rim 432. Along the bottom of opening of 426, 
defined by a portion of shelf 398, is a ledge 434 just below which are a 
pair of spaced posts 436. Disposed centrally along the upper margin of 
opening 426, and projecting away from the lower surface of control portion 
390, is a tongue 438 having a catch 440 on its free end (FIG. 17A). Spaced 
below and to the outside of posts 436 are a corresponding pair of cleats 
442 which face catch 440 at the same level. Rib 432 together with posts 
436 and shelf 434 all form a seat for display device 200. Lenses 431a, of 
course, face lens 430. Ledge 431c rests on posts 436 and is confined under 
cleats 442. Ledge 431b rests on rim 432 and is engaged by catch 440. 
Recessed below the level of shelf 398, and occupying a little more than 
half of control panel 390, is a large flat area 460 on which keyboard 110 
of FIG. 25 is seated as shown in FIGS. 10 and 14. In contrast with FIGS. 
10 and 14, however, the labels in FIG. 25 include both START HEAT and 
START AIR legends in substitution for the single START label shown in the 
earlier figures. Formed through panel 390 along the bottom of area 460 is 
a narrow slit 462 through which a flat flexible package or cable 464, 
within which are a plurality of conductive leads as indicated at 466, is 
inserted and fed as keyboard 110 is moved into position on area 460. 
A wide variety of keyboard assemblies are available in the marketplace, and 
the configuration of case 246 could be adapted to accommodate a number of 
them. The particular keyboard assembly embodied herein and illustrated in 
FIG. 25 is a very thin sandwich of several flexible layers of insulating 
material. From the perspective of viewing FIG. 25, there is an underlying 
layer on the bottom surface of which is a self-sticking coat of adhesive 
covered with a peel-off plastic-coated protective paper sheet which, 
during assembly, is peeled off to permit the keyboard assembly to be 
adhesively secured to area 460. An array of conductive contact pads, 
distributed in a pattern corresponding to the layout of "keys" or 
"buttons" depicted in FIG. 25, is printed upon the upper surface of that 
first flexible layer along with several interconnecting leads as defined 
in FIG. 5 and which continue within cable 464. 
Lying on top of that first flexible layer is a sheet of insulating material 
through which is defined an array of openings that expose each of the 
contact pads printed upon the upper surface of the first layer but cover 
the wiring also printed on that first layer. Such openings are known in 
the art as "cages". Overlying that layer of cages is a third flexible 
sheet of insulating material on the lower surface of which, facing the 
cage sheet, is printed another array of conductive contact pads 
individually disposed so as to be aligned over respective different ones 
of the contact pads printed on the first layer and, thus, also aligned 
with the cage openings. Also included on the undersurface of this third 
flexible layer is the necessary additional wiring, again as defined in 
FIG. 5, which similarly is extended down cable 464. As discussed 
previously in connection with FIG. 5, the contact pad printed on this 
third layer and underlying the START position in FIGS. 10 and 14 is 
separated into a pair of slightly spaced segments each having an 
individual printed connection and which individually underlie the 
respective START HEAT and START AIR positions as shown in FIG. 25. 
Printed on the upper surface of the flexible third layer is a grid in the 
form of a succession of laterally spaced narrow conductive lines that are 
all electrically connected together and to a conductor within cable 464. 
It is that conductive grid which serves as electrostatic shield 192 
previously discussed in connection with FIG. 5. Finally, a decal 468, 
carrying the printing indicated in FIG. 25 (or as indicated in FIG. 10 for 
a heat-only model), is adhesively fixed on top of the third layer and over 
the conductive grid. The intermediate cage-forming layer is sufficiently 
thin that only light finger pressure applied on any key or button area is 
enough to move the uppermost one of the underlying pads through the cage 
opening and into contact with the bottom contact pad, so as to complete a 
connection and thus close the "pushbutton". 
After keyboard assembly 110 has been affixed to surface 460, bezel 220 is 
cemented or otherwise secured so as to overlie the keyboard and define the 
pushbutton openings as well as to frame both battery compartment 224 and 
opening 426, bezel 220 generally lying on top of shelf 428. The opening 
over battery compartment 224 is sufficiently large to accept battery cover 
226 while the bezel strip at the bottom of opening 426 projects slightly 
over that opening in order further to confine lens 430 in place. 
Similarly, the surrounding portions of the bezel serve to additionally 
secure the edge margins of keyboard assembly 110. For the specific 
keyboard shown in FIG. 25, it is preferred that bezel 220 include a leg 
disposed between the pair of "start" buttons. 
Formed around the lower margin of skirt 284 of case 246 is a downwardly 
depending lip 470 having a downwardly-facing end surface aligned with the 
upwardly-facing surface of rim 381 around the margin of base 242. When 
case 246 is mated to base 242 and the lower ends of posts 252 are seated 
within wells 380, lip 470 closes the space between case 246 and base 242 
except at a gap 472 in lip 470, near the lower left hand corner of case 
246 as viewed in FIG. 18, and a plurality of gaps 474 formed in lip 470 
and distributed along the upper margin of case 246. When base 242 and case 
246 are joined together, those gaps define openings into the interior of 
housing 222. As seen in FIG. 12, gap 472 is disposed at the bottom of the 
housing when housing 222 is mounted on plate 240 so as to be vertically 
oriented. The purpose of these various openings defined by gaps 472 and 
474 will be set forth below. 
Again viewing the bottom of case 246 as shown in FIG. 18, a web 475 will be 
seen to extend all of the way between skirt 284 and an end wall 476 of 
battery compartment 224, the battery compartment being completed by the 
formation of an opposing end wall 478. Web 475 is located just above slit 
462 along the lower margin of area 460 and thus serves to rigidify the 
latter. Connected between skirt 284 and the pair of posts 252 along the 
lower margin of case 246 are webs 480 which are also formed integrally 
with the underside of sloping panel portion 292. Each of webs 480 defines 
a flat 482 disposed in alignment with about the middle of the opening 
defined by gap 472. The outer ends of posts 252 project beyond flats 482 
by a distance slightly greater than the thickness of printed circuit board 
244. 
Post 252, toward the upper left-hand corner of FIG. 18, is supported from 
the underside of area 460 by upstanding generally-triangular-shaped and 
space-opposed webs 484 and 486 each of which is slightly truncated in 
order to define respective flats 488 and 490 which are at the same level 
as flats 482. Moreover, the undersurface of ledge 406 adjacent to the 
remaining post 252 is also at the level of the different flats just 
discussed. The uppermost ones of these other posts 252 project beyond that 
level to the same extent as the lower posts 252. Included at the upper 
left-hand corner of the battery compartment as seen from the bottom in 
FIG. 18, and in alignment with opening 374 in base 242, is an additional 
hollow post 490 the outer end of which is also disposed at the level of 
the different flats and the undersurface of ledge 406. 
Circuit board 244 is dimensioned to be received within lip 470 and includes 
four openings 492 distributed in a pattern corresponding to the pattern of 
layout of posts 252 and each of a diameter to fit with only slight 
tolerance over the protruding ends of the respective posts. Thus, upon 
assembly, circuit board 242 rests upon all of the different flats, the top 
of additional post 490 and the facing surface of ledge 406. Circuit board 
244 has a thickness such that the outer end portions of posts 252 project 
through board 244 a distance just sufficient to enter into the wells 
defined within bosses 380 on panel 273 of base 242. Therefore, when screws 
250 are inserted from the bottom of base 242 and tightened into the bores 
of posts 252, circuit board 244 is clamped tightly into a fixed position 
within the housing. Also formed through circuit board 244 is an aperture 
494 which, when the circuit board is mounted in place over posts 252, is 
aligned with the bore of post 490. 
Board 244 is of conventional construction, being composed of a semi-rigid 
insulative substrate through which are formed a large plurality of small 
pin apertures each sized to receive the conventional wires from discrete 
electronic components and terminal pins which project outwardly from 
integrated circuits and the like. The underside carries a printed circuit 
defined in accordance with FIGS. 2-5. It typically may be formed by 
coating the undersurface with a thin layer of copper and then, using a 
conventional photoresist or similar masking technique, etching away 
selected areas of the copper so as to leave only the desired conductive 
paths that interconnect the various different ones of the pin apertures as 
needed to complete the circuitry and also to form a small conductive 
soldering ring surrounding each pin or wire-receiving aperture. At the 
same time, four much larger conductive pad areas, each about the size of a 
numbered pushbutton area of keyboard assembly 110 which is drawn to scale, 
are formed and disposed in positions to be aligned respectively with the 
fingers 334 of contacts 314-317 when those fingers project through opening 
366 in panel 273 upon mounting of housing 222 to mounting plate 240. That 
is, the crease 336 of each finger 334 constitutes an electrical contact 
which is wiped against a respective one of the large conductive pads, 
printed on the undersurface of circuit board 244, as housing 222 is 
mounted on plate 240. Accordingly, the wires secured to each of contacts 
314-317 are connected by creases 336 of fingers 334 into the circuitry 
defined on board 244 through the mere act of mounting housing 222 upon 
plate 240. 
A pair of electrically separate contact ring segments also are formed so as 
together almost to complete encirclement of opening 494. With reference to 
FIG. 2, those two rings constitute terminals 120 and 141. When a small 
screw is inserted through opening 374 in base 242 and threaded into the 
bore of post 490 through aperture 494, the head of the screw conductively 
bridges those two segments when the screw is tightened. Consequently, the 
screw head serves the function of jumper 143. Preferably, all of the 
plated and etched undersurface is coated with an insulating material 
except for the immediate sites of each of the different conductive pads 
and rings. 
Subject to a few constraints, the layout of the various different 
components on the upper surface of board 244 is primarily determined by 
space considerations and the necessary distribution of the printed wiring 
pattern on the underside of the board. One such constraint previously 
mentioned was the desirability of locating capacitor C13 physically close 
to the Vcc terminal of microcomputer 150. Another is to provide a series 
of connection apertures in a position convenient for the coupling of cable 
464 (see FIG. 22A) Of similar consideration would be the provision of 
another series of connecting apertures directly beneath display device 
200. Additionally, thermistor RT1 of temperature sensor 108 (FIG. 3) is 
located immediately inside the opening defined by gap 472. 
During operation, the various electrical components within housing 222 
dissipate a small quantity of heat. The dissipation of that heat creates a 
chimney effect between the lower opening defined by gap 472 and the upper 
openings defined by gaps 474 as well as other more upward openings through 
which there is a degree of leakage. This chimney effect creates a 
continual flow of room air into the lower opening at gap 472 and out of 
the more upwardly disposed openings. Being located just inside the opening 
defined by gap 472, thermistor RT1, therefore, is able to obtain an 
accurate reading of the actual temperature of the room air without 
distortion by, but taking advantage of, the heat dissipated by the other 
electrical components. 
For completing a connection between the conductors within cable 464 and the 
circuitry printed on board 244, a plurality of connectors 496 are 
employed. Each connector, as shown in FIGS. 22A and 22B, is necked down at 
its lower end to define a pin 498 which is received within a 
pin-connecting aperture in board 244. Projecting upwardly from the body of 
connector 496 is a central tong 500 on either side of which is a bent 
resilient finger 502. At the lower end of cable 464, the covering over the 
printed conductors 466 is cut away to expose the conductor ends. In this 
case, the upper and lower surfaces of cable 464 are simply continuations 
of the first and third flexible layers mentioned above in connection with 
the discussion of keyboard 110. Accordingly, some of conductors 466 are 
affixed to the upper surface of the first layer, while the others are 
affixed to the lower surface of the third layer. 
With a plurality of connectors 496 disposed in a row as indicated in FIG. 
14, it is only necessary to insert the lower end portion of cable 464 
between the rows of opposing fingers and in a manner such that each 
exposed contact end is slipped between the tong 500 and gripping fingers 
502 of the appropriate one of connectors 496. In this case, of course, the 
row of connectors 496 on board 244 is so disposed as to be aligned 
directly ahead of cable 464 as it emerges from slit 462. 
A different form of connector 506, shown in FIG. 23B, is employed to 
connect display device 200 into the circuitry. The central body portion of 
connector 506 is necked down at its lower end 508 to define a pin again 
receivable in a selected pin aperture formed in board 244. At its upper 
end, connector 506 has a projecting thumb 510 alongside a longer finger 
512 slightly bent at its outer end portion toward thumb 510. During 
assembly, thumb 510 and finger 512 are inserted through an appropriate one 
of pin terminals 431d in ledge 431c of device 200 which is disposed 
directly above the row 514 of connectors 506 disposed on the upper surface 
of board 244. Thumb 510 and finger 512 press against and make contact with 
the conductively plated interior of the corresponding pin terminal 
opening. 
In an alternative manner of securing device 200, a mounting rack 515 as 
shown in FIG. 23C is used. To this end, posts 436, tongue 438 and cleats 
442 are omitted, and rim 432 has another portion running between the 
locations of posts 436 as they actually are shown. Disposed just behind 
row 514 of connectors 506 as viewed in FIG. 14 are a pair of holes which 
seat the lower ends of legs 516 on rack 515. An array of shorter legs 517 
rest on top of board 244 in front of row 514. A row of openings 518 in 
rack 515 are aligned with respective connectors 506, so that thumbs 510 
and fingers 512 project about half way therethrough. Device 200 may be 
mounted on rack 515 before case 246 is placed on base 242, allowing 
testing before final assembly of the housing. Upon that assembly, ledges 
431b and 431c rest on rim 432 as extended. 
Transparent cover 228 is formed of a material such as polycarbonate. It 
includes a main flat panel 520 around the entire margin of which is a 
downwardly depending skirt 522 which, when cover 228 is in a closed 
position, is spaced alongside and outwardly from rim 394 with the lower 
margin of skirt 522 normally being slightly spaced above a ledge 524 which 
entirely surrounds rim 394 except at gap 396 (FIG. 17). 
On the undersurface of panel 520, equally spaced about the center of the 
rear margin of the panel and merged into the inner surface of that portion 
of skirt 522, are a pair of spaced blocks 526 and 528. Each block includes 
a lateral circular opening 530 which communicates with a passage 532 of a 
width slightly smaller than the diameter of opening 530. Depending 
downwardly from the inner surface and near the rear margin of panel 520, 
and spanning the distance between blocks 526 and 528, is a rib 534 that 
slants up toward the rear. 
With reference to FIGS. 17 and 17A, depending downwardly beneath and at the 
edges of gap 396 are a pair of respective webs 536 and 538. Spaced a short 
distance from gap 396 beyond each of webs 536 and 538 are another like 
pair of corresponding webs 540 and 542. Each of these webs includes a 
downwardly-opening generally-circular recess 544 open on its lower side to 
communicate with a slightly narrower passage 546. 
Each of openings 530 in blocks 526 of transparent panel 228 constitutes a 
hinge. Similarly, each of recesses 544 in webs 536 and 540 constitutes 
another hinge, while those same recesses 544 in webs 538 and 542 
constitute a still further hinge. Cooperating with all of those hinges in 
a hinge bar 550. As shown in FIG. 20, hinge bar 550 is of somewhat 
C-shaped cross section. Its lower leg 552 is generally straight but is 
bent slightly outward from a generally V-shaped bight portion 554. Its 
upper leg 556 curves smoothly away from portion 554 to present a convex 
outer surface. An ear 557 projects outwardly from each end of bight 
portion 554. 
Projecting laterally outward from one end of leg 552 is a hinge pin 558. 
Similarly projecting outwardly from the other side of leg 552 is another 
hinge pin 560. The outer end portion of leg 556 is necked down at 562. 
Projecting laterally outward from the end of that necked down portion of 
leg 556 is a pin 564 on one side and a pin 566 on the other. 
Hinge bar 550 swings within the opening 568 provided by gap 396. Pin 558 is 
captivated within recesses 544 of webs 536 and 540, while pin 560 is 
captivated within recesses 544 of webs 538 and 542. Bight portion 554 
faces generally in a downward direction and the outer curved surface of 
leg 556 rides alongside the bottom margin 572 of opening 568 as hinge bar 
550 swings about hinges 558 and 560. Bottom margin 572 is beveled inwardly 
in a direction downwardly from opening 568 as shown in FIG. 18. 
Pin 564 is captivated within opening 530 of block 526, while pin 566 is 
captivated within the identical opening within block 528. Thus, 
transparent cover 228 may, to a limited extent, be swung about pins 564 
and 566. Centrally disposed between approximately the rear sides of pins 
564 and 566, as viewed in FIG. 20, and projecting outwardly from the 
outside surface of leg 556, is a lug 570. 
With cover 228 in the closed position, the cover is hinged around pins 564 
and 556 so as to be swung over leg 556 to a position such that lug 566 
projects into the recess formed by the outside of rib 534. At the same 
time, hinge bar 550 has been swung downwardly within opening 568 so that 
lower leg 552 is approximately parallel with control panel 390. As cover 
228 is first swung away from its closed position, interference between lug 
570 and rib 534 retards rotation of pins 564 and 566 as a result of which 
hinge bar 550 first swings upwardly about pins 558 and 560 until the ears 
557 on the sides of bight 554 engage the lower side edges of opening 568. 
Thereafter, further opening of cover 228 causes it to complete its limited 
movement of swing, which may already have been started, about pins 564 and 
566. That limit is reached when skirt 522 touches the inside of leg 566. 
On still further opening of cover 228, ears 557 cam inside the side walls 
of opening 568 as hinge bar 550 is swung on around pins 558 and 560 until 
a limit is reached when the inside of leg 552 abuts the inner surface of 
skirt 284 of upper housing 242. 
When cover 228 has been moved to the fully opened position, the dimensions 
and the backward slope of control panel area 390 are such that it tilts 
backward a slight amount, so as to remain in the open position with 
respect to swinging about pins 564 and 566. At the same time, the 
frictional engagement of ears 557 with the side surfaces of opening 568 
retains hinge bar 550 in its open position. The double articulation 
provided by the combination of the two different sets of hinges enables 
cover 228 to be both fully closable and openable a full 
one-hundred-and-eighty degrees to a position in which it is entirely out 
of the way of operation of keyboard 110. 
Also projecting downwardly from the inner surface of panel 520 is a boss 
574. The latter has approximately the shape of and, when cover 228 is 
closed, is oriented with and aligned directly over the REVIEW pushbutton. 
Moreover, the lower end 576 of boss 574 is, with the cover nominally 
closed, spaced only slightly above or just at the surface of that REVIEW 
pushbutton. The material of cover 228 is slightly flexible and the slight 
normal spacing of the bottom of skirt 522 from ledge 524 allows pressure 
anywhere upon the exposed face of panel 520 to cause depression of the 
REVIEW button by boss 574 and thereby immediately provides a readout of 
temperature, time and day from device 200 without opening the cover. 
Repeated application of pressure upon cover 228, of course, would enable a 
user to conduct additional review as previously described, such as 
determining what is to happen next. At the same time, this operation 
cannot cause an alteration of any program step that has been stored. In 
addition, cover 228 serves as a dust protector and also as a deterrent 
against undesired pushbutton manipulation by others. Being transparent 
although it may be tinted, and also having the review actuation feature, 
there seldom is any need to open cover 228 unless a battery warning is 
observed or it is desired to make a change in the programmed operation. 
It will be observed that a wide variety of different features have been 
disclosed. Without limitation or ordering as to importance, it may be 
noted that a common temperature sensor is employed for control of either 
heating or air conditioning. Moreover, that sensor is disposed in a 
restricted air flow path by an arrangement which tends to prevent 
misleading readings that otherwise might result from transient air 
currents. The overall layout creates a chimney effect which insures that 
room air constantly is drawn through the unit in order to provide an 
accurate response. 
The particular hinge arrangement, including hinge bar 550, permits cover 
228 to be swung more than one-hundred-eighty degrees while yet allowing 
complete closure. This hinge arrangement achieves what may be termed a 
dual-detenting so as to insure that it opens and closes in proper 
sequence. Resilient contacts 314-317 exhibit a double action that permits 
contact both to the printed wiring and to the incoming supply and command 
leads. Those contacts also permit the unit readily to be removed from the 
wall simply by taking advantage of the different ears and lugs provided as 
between the housing and the mounting plate. 
Involving both battery and external alternating-current power supply, a 
rather sophisticated switching arrangement is provided in order to change 
between those two different supplies. Yet, the unit is arranged to run 
normally from the external alternating-current supply. Battery 152 not 
only provides a backup to the main power supply system but also enables 
retention of the stored user programs should there be a power failure or 
should the user desire to displace the controller to another location for 
reasons already indicated. In addition, the unit warns the user when it 
becomes time to replace battery 152. 
Electrostatic screen 192 disposed over keyboard 110 serves to protect 
against damage to the sensitive microcomputer. In addition, there are 
various filters and optical couplers to provide suppression of transients 
and other spurious signals which otherwise might be introduced by reason 
of signals appearing on the incoming alternating-current power supply or 
from other sources. Additional filtering is included in order to protect 
against radio-frequency interference. An included time delay prevents 
control operation in an undesired manner which otherwise might even cause 
a pilot light in an associated heating or cooling unit to be extinguished. 
Even though involving only what basically is a simple 
resistance-capacitance circuit, the temperature sensor is caused to be 
sufficiently linear as to be accurate within one degree Fahrenheit over 
the rather broad functional range. The unit gives notice that the control 
is calling for heat, serving to assure the user that heat is being 
supplied by a "silent" arrangement such as a heating system which uses hot 
water, steam or radiant supply. Even in the case of a forced air system, 
the indicator serves to inform the user that external operation has been 
commanded prior to the expiration of the time delay that often occurs 
between initial energization and the operation of blowers or the like. 
The software incorporated is of special advantage. For example, the order 
of data entry established makes it possible to "write a sentence" instead 
of having to make constant use of an "enter" key. The day codes assigned 
to the numbered entry keys allows substantial flexibility within the 
user's normal work week. On the other hand, the user who has a rather 
non-typical schedule of events easily can employ the individual day codes 
to arrange a program in accordance with his own unique schedule. 
Adding to flexibility is the feature of temporary override that affects 
only one previously-programmed instruction without, nevertheless, removing 
that previous instruction. Similarly, the vacation override enables a 
different program to be followed during a longer period of time and again 
without disturbing the normal program. 
Having both Fahrenheit and Celsius scales, the thermostat contemplates a 
possible switchover in common usage from one to the other. Moreover, the 
thermostat features a manner of conversion which effects a change of an 
entire sequential program as between Fahrenheit and Celsius, while at the 
same time changing the corresponding visual display. 
The particular unit as embodied is capable of accepting up to twenty-three 
set points. Considering the various different day code options, this means 
that the user can establish in excess of one-hundred different temperature 
set points within any given week. 
In the overall, therefore, the user is enabled to program the establishment 
of his own confort level which he desires over a wide variety of different 
periods throughout an entire week. At the same time, the user can achieve 
energy conservation by focusing rather specifically upon fairly narrow 
time periods during which demand desirably should be lessened in order to 
effect such conservation. Moreover, the thermostat affords simultaneous 
control of both heating and air conditioning without requiring that the 
user act to switch between the two systems. Thus, he is further able to 
program the establishment of his own complete "comfort zones". 
Certain aspects of the present invention are described and claimed in 
concurrently-filed co-pending applications Ser. No. 69,978 of James B. 
Waite and Myron Yoknis under the title "Thermostat" and Ser. No. 70,220 of 
Robert M. Neel under the title "Thermostat Assembly", both being assigned 
to the same assignee as the present application. 
While a particular embodiment of the invention has been shown and 
described, and numerous modifications and alternatives have been 
suggested, it will be obvious to those skilled in the art that other 
changes and modifications may be made without departing from the invention 
in its broader aspects. Therefore, the aim in the appended claims is to 
cover all such changes and modifications as fall within the true spirit 
and scope of that which is patentable.