Abstract:
A switching controller that allows a load to be controlled from either a switched wall outlet or a switch local to the load. A standard “3 way” SPDT wall switch replaces the normal SPST switch to allow for simple generation of a control pulse that is detected by the local control device to allow a change of state of the power provided to the load from either the wall switch or a manual switch directly connected to the control device.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     N/A  
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002]     N/A  
       BACKGROUND OF THE INVENTION  
       [0003]     In household electrical systems, it is common to supply a wall outlet with electrical power through a wall switch positioned near an entryway. A lamp may then be plugged into the switched wall outlet. If the switch at the lamp is left on, the lamp can be turned on and off from the wall switch. This allows a person entering a dark room to turn on the lamp from the wall switch and avoids the need to search for the lamp switch in the dark.  
         [0004]     Commonly, however, it is more convenient to turn the lamp off using the switch near the lamp. As a result, when the person leaves and later re-enters the room after dark, an attempt to turn on the lamp at the wall switch fails. Also, if the wall switch is turned off, the lamp cannot be turned on using the lamp switch. The bedside lamp illustrates the problem. While it is convenient to turn the lamp on using the wall switch when entering the room after dark, it is more convenient to use the switch near the lamp to turn the lamp off when retiring. As a result, in the morning when the room is well lit by daylight, the bedside lamp switch is typically left switched off. Thus at nightime when the room is reentered, the wall switch can&#39;t be used to turn the lamp on again.  
         [0005]     It would thus be desirable to provide a switching device that can be used to control a lamp that is plugged into a switched outlet from either the wall switch or the lamp switch.  
         [0006]     Various devices have been disclosed over the years to resolve this problem. Platzer (U.S. Pat. No. 3,872,319) requires two outlets, switched and un-switched, with local circuitry to provide the capability. Liang (U.S. Pat. No. 4,383,186) describes the use of relays to provide the various switching states but also suffers from the need to use two wall outlets to control a single lamp. Bennett (U.S. Pat. No. 5,574,319) overcomes the two outlet requirement by requiring the operator to flip the wall switch off and then on again for each desired change in lamp state. Bennett suffers from the additional problem that if the wall switch is left in the “off” state, the local switch cannot be used to turn the lamp on again. Logan (U.S. Pat. No. 6,710,553) provides a variation on Bennett that allows the original lamp switch to be used as the local switch, as well as providing an alarm if the wall switch is accidentally left in the “off” position.  
         [0007]     The implementations of the above cited patents all have the disadvantages of either requiring two wall outlets or double actuation of the wall switch by a user. Moreover, if the user leaves the wall switch in the wrong state the lamp switch becomes inoperative. There is a continuing need to have a control device that allows for the simple actuation of a wall switch, does not require two electrical outlets, and has no failure modes.  
       BRIEF SUMMARY OF THE INVENTION  
       [0008]     This invention relates to electrical power control circuitry and more particularly to apparatus for controlling a lamp or other electrical load using either a remote wall SPDT switch or a local switch to control the power delivered to the load.  
         [0009]     In accordance with the present invention, apparatus is provided for controlling a lamp or other electrical load that is connected to a wall socket under the control of a wall mounted switch. The state of the lamp (either on or off) is toggled when either the wall mounted switch is moved to its opposite position or the local switch associated with the controlling device is actuated. The local switch may be any one of a toggle switch, a pushbutton, or a touch switch. The apparatus includes control circuitry operative in response to a control signal from the wall switch or from the local switch.  
         [0010]     The control signal from the wall switch is provided by the use of a break before make SPDT switch with both of its poles tied together. This creates a brief interruption to the flow of power to the wall socket, which is detected by the control circuit to change the lamp state. The control signal from the local switch is provided by a change in the switch state caused by manual actuation of the local switch.  
         [0011]     In a further embodiment, the local switch may be used to control the brightness levels of the lamp, providing the equivalent of a three way bulb for the price of a simple bulb. As an alternative, the local switch may be used as a continuous dimmer control.  
         [0012]     These and other objects, features and advantages of the invention will be more clearly understood by considering the following detailed description of a preferred embodiment of the invention. In the course of this description, frequent reference will be made to the attached drawings. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0013]      FIG. 1  is a schematic block diagram of the invention;  
         [0014]      FIG. 2  is a circuit diagram of a microprocessor based implementation showing a preferred embodiment;  
         [0015]      FIGS. 3   a  and  3   b  show the flow chart of the operation of microprocessor implementing the control functions;  
         [0016]     FIGS.  4  shows one physical package for the circuitry of  FIG. 2 ;  
         [0017]      FIG. 5  shows another package of the circuitry for inclusion in a lamp socket; and  
         [0018]      FIG. 6  shows a package of the circuitry in a separate socket. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0019]     Referring to  FIG. 1 , wall switch  102  controls the flow of power from supply  101  to wall outlet  103 . Power is maintained at wall outlet  103  for either position of wall switch  102 , but when the switch is toggled, a brief interruption of the power occurs as the switch armature moves from one pole to the other. Wall switch  102  is a single pole double throw (SPDT) switch, readily available in electrical supply stores where they are commonly known as “3 way” switches. A pushbutton which is normally closed could be used as well.  
         [0020]     Control device  105  is connected to wall outlet  103  via wall plug  104 . Used in conjunction with wall switch  102 , it provides the key mechanism for effecting the load control from either of the two locations. Power supply  110  provides low voltage DC power for the operation of the other circuits that make up control device  105 .  
         [0021]     AC timer  106  is used to detect the momentary power loss when wall switch  102  is actuated. It is reset with each zero crossing of the AC supply  101 . For 60 Hz power, this occurs approximately every 8 milliseconds, or 10 milliseconds for 50 Hz power. As an alternative, it could be reset once each cycle, with periods twice as long as mentioned above. Timer  106  is set to expire with a period of approximately 10 milliseconds, so that an expiration of the timer indicates that wall switch  102  has been actuated.  
         [0022]     An expiration signal from timer  106  is sent to power state register  107  which in turn controls load control  108  to deliver power to load  111 . In the simplest embodiment, power state register has two states, ON and OFF, which cause load control  108  to deliver power, or not, respectively. Each time an expiration signal is received from timer  106 , power state register  107  is toggled to its opposite state, thereby allowing wall switch  102  to control the power delivered to load  111 . Load control  108  may be any one of a variety of electrically controlled power switches, for example, a relay or a solid state device such as a triac.  
         [0023]     Local switch  109  provides the other mechanism for controlling power to the load. Each time it is actuated, power state register  107  toggles to its opposite state, controlling power to load  111  via load control  108 . Local switch  109  may be any kind of switch, including pushbutton, toggle, rotary, touch, etc.  
         [0024]     A mechanism must be provided such that power state register  107  retains its state during the power interruption caused by the actuation of wall switch  102 . Typically this is done by having power supply  110  have sufficient capacitance to provide enough energy to the power state register  107  for the duration of the power interruption. As an alternative embodiment, power state register  107  can be built out of non volatile semiconductor memory, such as electrically erasable programmable read only memory (EEPROM) or flash memory.  
         [0025]     In an alternative embodiment, power state register  107  may have more states than just two. For example, three brightness levels for a lamp may be achieved by assigning four states to power state register, representing off and three brightness levels. For this embodiment, load control  108  must be capable of delivering partial power, not just on or off. Details of how this control is effected will be described later in this detailed description.  
         [0026]     Referring to  FIG. 2 . as a preferred embodiment of control device  105  based on the use of a single chip microcontroller to implement ac timer  106 , power state register  107 , and a capacitive touch switch as local switch  109 . A typical choice for microcontroller  211  would be part number 12C508 from the Microchip corporation, but there many inexpensive microcontroller devices from a variety of vendors that would serve equally well.  
         [0027]     Power supply  110  is a conventional half wave rectified, capacitor filter supply of a design well known to those familiar with the art. Diode  201  rectifies the AC signal to DC, resistor  202  allows for a voltage drop from the high AC voltage to the low DC voltage (typically 3-5 volts), and capacitor  103  provides for energy storage and delivery during the half cycle of AC when diode  201  is not conducting as well as during the power interruption when switch  102  is actuated. Zener diode  204  provides voltage regulation.  
         [0028]     Resistor  205  is a high value resistor that allows the microcontroller  211  to sense the zero crossings of the AC supply to reset the AC timer. As will be seen in a discussion of the software, this zero crossing signal will also be used to help implement the touch switch as well as to control the timing of an actuation signal to the triac  210  through resistor  209 .  
         [0029]     Resistors  207  and  206  as well as touch point  208  make up the touch switch. At each zero crossing of the AC supply a pulse will be put out on the TOUCH_OUT output of microcontroller  211  and sensed several microseconds later. If a person  212  is touching sense point  208 , the RC delay of resistor  207  and the capacitance of person  212  (typically greater than 30 picofarads) will prevent the pulse from being sensed on input TOUCH_IN. If there is no person in contact with sense point  208 , then the pulse will be sensed on input TOUCH_IN. This will be used to control the power to the load as described in the flowchart in  FIGS. 3   a  and  3   b.    
         [0030]     Triac  210  implements load control  108  in conjunction with microcontroller  211 . Resistor  209  limits the flow of current through microcontroller  211 .  
         [0031]     The flowchart of  FIGS. 3   a  and  3   b  shows the software implementation for a control device that implements both the local and remote control mechanisms, as well as providing a three level power control for lamp dimming.  
         [0032]     The PowerState variable represents the value of power to be delivered to the load. It takes on values 0, 1, 2, and 3 which represent off, one third, two thirds power, and full power, respectively.  
         [0033]     The LastTouch variable is used to keep track of a person touching the terminal for the local switch which in the illustrated embodiment is a touch switch. The touch switch is sampled on each zero crossing of the AC line and an actuation is defined to occur when a person is touching the sense point and was not on the previous sample. LastTouch has the value 1 if the previous sample indicated a touch.  
         [0034]     Step  301  waits for a zero crossing of the AC line. The subsequent steps depend on this synchronization event.  
         [0035]     Steps  303  through  306  are used to detect an AC power interruption and change the power state appropriately upon such detection. Step  303  checks to see if the timer has expired. Since zero crossings occur approximately every 8 milliseconds and the timer is set to expire after 10 milliseconds, an expiration of the timer means that AC power had been lost and the program waited at step  301  for longer than a normal half cycle of the AC line. If the timer expires, the program goes to step  304  which checks to see if any power had been delivered to the load. If PowerState has any value but 0 , some power is present and the program turns the power in step  305  by setting PowerState to 0 . If PowerState has a 0 value, then power was off, and the program turns the power on in Step  306  by setting it to 3, for full power. As an alternative, the power can be configured to bring the power up at a value less than full power, if that was deemed preferable for some applications.  
         [0036]     For the final handling of the power interruption algorithm, the timer is reset to its starting value in step  307 .  
         [0037]     Steps  308  through  314  deal with the handling of the touch switch. Steps  308  through  310  assert the TOUCH_OUT pin high, wait 5 microseconds, and then read the TOUCH_IN pin. If no one was touching the sense terminal, the TOUCH_IN pin will be high because it is driven by the TOUCH_OUT pin. If , however, a person is touching the terminal, the TOUCH_IN pin will read low because the short delay is not enough to allow the pin to become high, given the delay caused by resistor  207  and body capacitance of the person touching the sense terminal.  
         [0038]     If a touch is sensed, the program goes to step  311  and checks whether the touch was present the last time through the loop. If so, then this is not the moment of initial touch, and no change is made to PowerState. If, however, it is the initial touch, then the PowerState variable is advanced to its next valid value in step  312 . This causes successive touches on the sense terminal to advance the control device through all of the brightness levels, including off.  
         [0039]     Steps  313  and  314  set the LastTouch variable to the current state of the sense terminal, so that it has a valid value for the next pass through the loop. Step  315  resets the TOUCH_OUT pin to be ready for the next cycle.  
         [0040]     Step  316  disables control power to the triac at the zero crossing. This is in preparation for the following steps.  
         [0041]     Steps  317  through  320  control the power delivered to the load by triac  210  in accordance with the value of the PowerState variable. The power control employs a phase control mechanism, which itself is well known to those familiar with the art. A more detailed description of how triac phase control works may be found, as an example, in Teccor Electronics document AN1003, “Phase Control Using Thyristors”, 2002. A simple summary for the purposes of this description is that the power delivered to the load is a function of the delay from AC zero crossing at which the triac is turned on. The longer the delay, the less power is delivered to the load.  
         [0042]     Step  317  checks the value of PowerState. If 0, no power should be delivered, and the program goes back to step  301  to wait for the next zero crossing of the AC line.  
         [0043]     If PowerState is 1, then we wish to deliver one third power to the load and this is accomplished by waiting approximately 60% of the half cycle before turning on the triac. For a 60 Hz line, this is about 5 milliseconds. Step  318  implements this.  
         [0044]     If PowerState is 2, step  319  sets a delay of 3.5 milliseconds.  
         [0045]     If PowerState is 3, full power requires that the triac be turned on without appreciable delay.  
         [0046]     Steps  320  activates the triac to deliver power to the load.  
         [0047]     Although the preferred embodiment described above shows a four state power level system, it should be apparent to those skilled in the art that modified embodiments can provide either more or fewer power levels.  
         [0048]      FIG. 4  shows one packaging configuration for control device  105 . The circuitry is placed on a printed circuit board  403  inside a plastic case  401  through which the lamp power cord  402  passes. The AC hot side of the cord  402  is cut to allow the control device to switch the power to the lamp side of the cord. Connection is made between the printed circuit board  403  by three pins  404  which pierce the insulation on cord  402  and touch the inner conductors. As an alternative embodiment, screw or friction terminals could be used. A connection from the circuit board  403  is made to metal plate  208  for the touch switch. Cover  405  protects the user from harmful voltages.  
         [0049]      FIG. 5  shows an alternative package in which the control device is packaged on a printed circuit board  501  housed inside a standard metallic lamp socket  502 . The metal shell of the lamp socket serves as the sense terminal. The socket may be placed in any lamp base, with base  503  shown as an example  
         [0050]      FIG. 6 . shows yet another alternative package in which the control device printed circuit  501  is placed inside a lamp socket  602  which screws into the existing socket of a lamp via male threads  603  and provides a socket for the bulb via female threads  604 . The metal shell of the lamp socket serves as the sense terminal.  
         [0051]     It will be recognized that any of the package configurations shown in  FIGS. 4-6  could accommodate a mechanical switch instead of a touch switch. It is also to be understood that the specific embodiment of the invention, which has been described, is merely illustrative and that modifications may be made to the arrangement described without departing from the true spirit and scope of the invention