Control device using light-emitting diodes for both manual input and display of data

A light-emitting diode is used both for receiving data from an operator to change the logic state of a device and for displaying the entered data back to the operator. Current is selectively applied to the diode to display the data, but on an alternate basis the photo-current produced in the light-emitting diode by surrounding illumination is sensed and the data are received by detecting the fall-off in the photo-current caused by the operator covering the light-emitting diode. This technique is advantageously employed for the input and display of ink slide settings for a rotary printing machine by using a light-emitting diode matrix or bar graph display subject to finger-tip control by the operator. The diode matrix is scanned by repetitively and sequentially inhibiting the lighting current to the individual light-emitting diodes so that they may be sequentially connected to a photo-current monitoring circuit via a multiplexer under control of a clock circuit.

FIELD OF THE INVENTION 
This invention relates generally to data display and input devices, and 
more particularly to a data input and display device in a control system 
for adjustment of the ink dosing elements in a rotary printing machine. 
Specifically, the invention relates to such a data input and display 
device having a control panel including a matrix of light-emitting diodes 
for display of ink slide displacements. 
BACKGROUND OF THE INVENTION 
In a rotary offset printing machine, it is well known to use an array of 
ink-dosing elements or slides arranged across the width of the printing 
machine for zonally regulating the density of ink printed on the printed 
sheet. The density of ink is increased or decreased by displacement of the 
ink slides under the control of an automatic ink feed control system. At 
the present time all of the major printing machine manufacturers sell 
automatic control systems for this purpose. A light-emitting diode matrix 
or bar graph display has been used in some of these systems for indicating 
the ink slide displacements. 
In a known control system of this kind, as described in West German patent 
publication No. 3,147,312, a light pen is provided for entry of set-point 
data and control commands, and has a light receiver cooperating with the 
light-emitting diodes. For inputing each individual displacement value for 
a respective ink slide, a printer puts the light pen on the light-emitting 
diode corresponding to the value in the light-emitting diode row for the 
respective ink slide, and receives a light signal emitted by the 
light-emitting diode as a result of a short duration current pulse, the 
light signal being detected by an electronic control unit connected to the 
light pen and being evaluated for the adjustment of the respective ink 
slide. The light-emitting diode in proximity with the light pen is 
recognized by the fact that the light-emitting diodes receive the current 
pulses in a predetermined sequence. To enable the light-emitting diodes to 
be used for display purposes at the same time, the current pulses are so 
short in duration that the light-emitting diodes appear to the human eye 
to be non-illuminated or only weakly illuminated. Those light-emitting 
diodes which provide a display, on the other hand, are additionally given 
a relatively long current pulse which makes them appear to the human eye 
as brightly illuminated. The light pen is connected to operate only during 
the times of the short current pulses and cannot therefore detect the 
display pulses. A disadvantage of this kind of control system is that a 
light pen with a light receiver is required for entering set-point data 
and commands, and the light pen is connected to the control unit via a 
cable. The light receiver may, for example, be disturbed by stray light or 
reflections, and the cable can readily be damaged. 
SUMMARY OF THE INVENTION 
The primary object of the invention is to increase the reliability of data 
entry to a control system of the kind using light-emitting diodes for 
display of input data. 
Another object of the invention is to simplify the entry of data to a 
control system of the kind having light-emitting diodes for display of 
input data. 
A specific object of the invention is to eliminate the need for external 
input devices for a control system of the kind using light-emitting diodes 
for the display of data. 
Briefly, according to the invention, any falloff in the photo-current 
produced in the light-emitting diodes by surrounding illumination is 
detected and evaluated as an input signal. For manual data entry, for 
example, the operator covers a selected light-emitting diode with his 
finger tip, causing the photo-current produced in the light-emitting diode 
to be interrupted, and the interruption in photo-current is detected by an 
electronic monitoring circuit. For the adjustment of ink slides in a 
printing machine, for example, the printer may set the displacement of a 
desired ink slide by covering a selected light-emitting diode in a row or 
column of light-emitting diodes corresponding to the desired ink slide. 
Thus by finger tip control the printer can input set-point data and 
control commands without the need for an additional device such as a light 
pen. 
In accordance with another important aspect of the invention, the entry of 
data at a particular light-emitting diode is registered by turning on the 
same light-emitting diode. Illumination of the light-emitting diodes 
covered during data entry immediately shows the operator whether the input 
has been detected and evaluated. 
In a preferred embodiment of the invention, a multiplexer under control of 
a clock circuit repetitively and sequentially connects each light-emitting 
diode to a monitoring circuit for detecting the photo-current and at the 
same time the light-emitting diode (which may have been turned on for 
display purposes) is temporarily disconnected from a lighting voltage 
source. Electronic switches are used to rapidly and reliably scan the 
light-emitting diodes for obtaining input data. According to an important 
aspect of the invention, the display of set-values already entered or 
actual-values occurring during operation of the control system are 
unaffected by the scanning or data entry process, because the time during 
which the light-emitting diodes are temporarily disconnected from the 
lighting voltage source is so short in duration that the temporary 
extinction of the light-emitting diodes cannot be perceived by the human 
eye. 
In a preferred embodiment of the invention, each light-emitting diode is 
alternately connected by parallel switching circuits to the lighting 
voltage source or to the monitoring circuit. In this way all of the 
light-emitting diodes in a large matrix are monitored by the monitoring 
circuit. 
According to another important aspect of the invention, in order to detect 
any fall-off in the photo-current of the light-emitting diodes, a 
current-to-voltage converter is connected in series with the monitoring 
circuit.

While the invention has been described in connection with the preferred 
embodiment, it will be understood that there is no intention to limit the 
invention to the particular embodiment shown but it is intended, on the 
contrary, to cover the various alternative and equivalent forms of the 
invention included within the spirit and scope of the appended claims. 
DESCRIPTION OF THE PREFERRED EMBODIMENT 
Turning now to the drawings, there is shown a schematic diagram of a rotary 
offset printing machine generally designated 10 and a data input and 
display unit 11 according the present invention which are interconnected 
by a cable 12. The printing machine 10 includes two printing units each 
having a plate cylinder 13 which is fed with printing ink via rollers (not 
shown) of a respective inking unit generally designated 14. Blanket 
cylinders 15 transfer the ink from the plate cylinders 13 to the paper 16 
being printed. The paper 16 passes between the blanket cylinder 15 and 
impression cylinder 17. 
The inking units 14 are of conventional construction and are of the kind 
including a duct 18 cooperating with a duct roller 19 to define a 
reservoir of ink. In order to zonally adjust an ink profile across the 
width of the printing machine, the flow of ink from each inking unit 14 is 
regulated by an array of ink dosing elements or slides 20 disposed at the 
base of the duct 18 and which are individually displacable with respect to 
the duct roller 19. The ink slides are automatically displaced by 
actuators 21 such as stepper motors in order to set a desired gap between 
the duct roller 19 and the end of each ink slide 20 abutting against the 
duct roller. The width of the gap defines the amount of ink transferred 
from the ink duct 18 to the respective plate cylinder 13. 
The actuators 21 are adjusted in the conventional manner by a position 
adjusting microcomputer 22 as described, for example, in Schramm et al. 
U.S. Pat. No. 4,200,932 issued Apr. 29, 1980. The position adjusting 
microcomputer 22 receives, via the cable 12, set-point values from the 
data input and display unit 11. For the entry and display of ink density 
set-point values, the data input and display unit 11 includes a control 
panel 23 comprising a matrix 24 of light-emitting diodes. The data input 
and display unit 11 is also used in the conventional manner as a control 
panel for a number of other machine functions, for example, for control of 
printing register. 
Turning now to FIG. 2, the matrix 24 of light-emitting diodes 25 is shown 
in greater detail. In order to provide a graphic display of the 
displacement of the ink slides 20, the matrix 24 has a particular column 
k.sub.1 to k.sub.n for each of the n ink slides 20 in a single one of the 
inking units 14. For simplification, the matrix 24, at any given time, 
serves to enter or display ink slide displacements for a selected one of 
the inking units 14. Each of the m rows in the matrix corresponds to a 
discrete gradation of ink slide displacement. Each gradation, in other 
words, represents a specific level of ink density printed on the printed 
sheet 16. It should be noted, however, that the actual displacement of the 
ink slides need not have a precise linear relationship to the levels of 
ink density, for example, the levels could correspond to displacement 
offsets from preselected reference positions. As further shown in FIG. 2, 
the matrix 24 could give a kind of bar graph display including segments of 
illuminated 26 and non-illuminated 27 light-emitting diodes 25. The 
non-illuminated diodes 27, for example, represent the gap between the ink 
slides 20 and their respective duct roller 19. Alternatively, for example 
to conserve lighting power, only one diode in each column could be 
illuminated such as the uppermost diode shown illuminated in FIG. 2 in 
each column of the matrix 24. 
Turning now to FIG. 3 there is shown a simplified schematic diagram 
generally designated 30 showing how the light-emitting diodes 25 are used 
for both entering and displaying data such as control commands and 
set-points. For illustration purposes, only two light-emitting diodes 25 
are shown. Each of the light-emitting diodes 25 is connected in series 
with a current limiting resistor 31 and a switch 32 connected to a live 
conductor 33 fed with the required lighting voltage U.sub.b. In parallel 
with the respective resistor 31 and switch 32, each light-emitting diode 
25 is connected via a switch 34 to the input of a current-to-voltage 
converter generally designated 35 including an operational amplifier 36 
and a negative feedback resistor 37. The negative input of the operational 
amplifier 36 provides the input of the current-to-voltage converter 35 and 
the positive input of the operational amplifier 36 is grounded. Therefore, 
assuming that the input offset voltage of the operational amplifier 36 is 
minimal, the input current to the current-to-voltage converter 35 passes 
through the resistor 37 due to the negative feedback, and therefore the 
(negative) voltage on the output 38 which appears across the resistor 37 
is proportional to the input current. It should be noted that according to 
the photovoltaic effect, the illumination of a semiconductor p-n junction 
causes a forward voltage drop across the junction, so that the 
photo-current flows in the reverse direction across the junction. 
Therefore, the photo-current from the light-emitting diodes cause a 
negative voltage at the output 38 of the current-to-voltage converter. 
The output of the current-to-voltage converter 35 is fed to a monitoring 
circuit 39 which evaluates the voltage at the output 38 of the converter 
35. The monitoring circuit 39 also receives signals from a clock circuit 
40, which repetitively closes the switches 34 in a predetermined sequence. 
In order to selectively turn on the individual light-emitting diodes 25 to 
display data such as entered set-values or existing actual-values, the 
corresponding switches 32 are closed under control of the monitoring 
circuit 39. The light-emitting diodes 25 corresponding to the data to be 
displayed are then connected to the lighting voltage U.sub.b and are 
illuminated. The resistors 31 regulate the current applied to their 
respective light-emitting diodes 25 when their respective switches 32 are 
closed. 
To enable data to be entered at any time, the clock circuit 40 repetitively 
and sequentially opens and closes the switches 34. When a switch 34 for a 
light-emitting diode 25 is closed, the switch 32 associated with this 
light-emitting diode is temporarily open to disconnect the light-emitting 
diode from the lighting voltage 33. The switching times are so short in 
duration that the human eye does not perceive the extinction of the 
light-emitting diode. When the switch 32 is open and the switch 34 is 
closed for a particular light-emitting diode 25, the illumination 
surrounding the light-emitting diode causes a photo-current to flow from 
the light-emitting diode to the current-to-voltage converter 35. The 
monitoring circuit 39 receives the corresponding voltage from the 
converter output 38, and recognizes the build-up of the (negative) voltage 
during the closed phase of the switch 34 as the non-input of data 
corresponding to the light-emitting diode selected for evaluation at that 
time by the clock circuit 40. 
The entry of data is illustrated in FIG. 4. To adjust the displacement of 
an ink slide to a selected level, the printing machine operator uses his 
finger 41 to cover the light-emitting diode 25 in the column k and row z 
corresponding to the ink slide to be adjusted and the ink density level to 
be selected, respectively. As a result, the selected light-emitting diode 
25 is shielded from the surrounding illumination, so that on closing of 
the corresponding switch 34 no substantial photo-current is produced in 
the light-emitting diode. Therefore, at this time a corresponding 
(negative) voltage does not build-up at the output 38 of the 
current-to-voltage converter 35, and in response the monitoring circuit 39 
recognizes the entry of an adjustment command. As specifically described 
below in connection with FIG. 5, the monitoring circuit 39 responds to the 
entry of the command by activating the corresponding switch 32 so that the 
light-emitting diode covered by the operator becomes illuminated to 
display the input command. 
As shown in FIG. 4, the illumination surrounding the light-emitting diode 
could be provided by light sources such as incandescent bulbs 42 built 
into the control panel 23. The incandescent bulbs 42 could, for example, 
ensure that the light-emitting diode 25 is surrounded by a relatively 
constant level of illumination. As further described below, however, the 
monitoring circuit 39 can be constructed to be relatively insensitive to 
the actual level of the surrounding illumination. Therefore, conventional 
light sources 43 apart from the control panel 23 may provide the 
illumination surrounding the light-emitting diode 25. The conventional 
light sources 43, for example, are overhead lights. 
To enable just one light-emitting diode 25 to be covered by one finger 41 
without any great skill, the distance between the light-emitting diodes 25 
should correspond at least to the diameter of the finger tip. Auxiliary 
means could be used, however, to cover the light-emitting diodes. For 
certain recurring adjustments, for example, templates aligned with the 
control panel 23 could be used to cover selected light-emitting diodes. As 
further described below, however, recurring adjustments could be stored 
electronically in computer memory. 
The present invention has been described for the entry of ink density 
set-values on a rectangular matrix of light-emitting diodes. In this case 
the display provided by the matrix is analogous to the ink slide 
displacements. For other kinds of data entry, however, the light-emitting 
diodes could be arranged according to any desired format. Alphanumeric 
labels, for example, could be provided for indicating the command function 
associated with a particular light-emitting diode. For a printing machine, 
additional light-emitting diodes could be labelled and set aside for the 
control of register adjustment or for adjusting dampening units (not 
shown) associated with the printing machine. Although these commands could 
be diverse from the ink slide settings, electronically the light-emitting 
diodes associated with these other commands could be treated as an 
additional column of the diode matrix. 
Turning now to FIG. 5, there is shown a detailed schematic diagram of a 
preferred embodiment of the present invention. This preferred embodiment 
assumes that all of the light-emitting diodes 25, regardless of their 
function, are electronically arranged in a rectangular matrix. This 
electronic arrangement simplifies the opening and closing of the lighting 
current switches 32 and the photo-current switches 34 via row and column 
addressing of the matrix. As a further simplification, the clock circuit 
40 addresses both the lighting current switches 32 and the photo-current 
switches 34. From FIG. 5, it is recognized that this further 
simplification is made possible by using a microcomputer 50 as an 
important part of the monitoring circuit 39. The microcomputer 50 is 
synchronized to the addressing or scanning by the clock circuit. By using 
the microcomputer, an image table or array is provided in the computer's 
memory to store the desired states of the lighting current switches 32. 
The microcomputer 50 has a first set of output lines (OUT1) providing a 
separate binary signal for each column k of the matrix. This binary signal 
specifies whether the light-emitting diode 25 in the particular row z 
addressed by the clock circuit 40 should be turned on or off. 
As shown in FIG. 5, the clock circuit 40 includes a synchronous binary 
counter 51 providing a row address signal on a set of 4 address lines 
generally designated 52. The synchronous binary counter is, for example, a 
standard CMOS part number 4029. The outputs Q.sub.3, Q.sub.2, Q.sub.1, 
Q.sub.0 specify a four-bit binary row address number z. Therefore it is 
apparent that the number of rows m is 16 for the circuit shown in FIG. 5. 
The binary counter 51 is clocked by an oscillator generally designated 53 
comprised of standard CMOS NOR gates, which are standard CMOS part number 
4001. The oscillator 52 includes a frequency setting capacitor 54 and 
associated resistors 55 and 56. The resistance and capacitor values are 
selected to obtain a frequency of oscillation of about 400 hertz. This 
particular frequency sets a scanning rate of 25 hertz for the entire 
matrix and a duration of 2.5 milliseconds for inhibiting the lighting 
current and evaluating the photo-current from an individual light-emitting 
diode. The resistors 55 and 56, for example, have a value of 150 K ohms, 
and the capacitor 53, for example, has a value of 0.01 microfarads. 
In order to address the lighting current switches 32, the address lines 52 
from the counter 51 are applied to the select inputs of a multiplexer 57 
provided for each column of the matrix 24. The multiplexer 57 is, for 
example, standard CMOS part number 4067. Each output of the multiplexer 57 
is fed to the switch 32 for a particular light-emitting diode 25. Due to 
the relatively large number of multiplexers addressed by the counter 51, 
buffers 58 drive the address lines 52. The buffers 58 are included in a 
standard CMOS integrated circuit part no. 4050. 
As shown FIG. 5, each lighting current switch 32 is comprised of drivers 59 
and transistors 60. The drivers 59 are included in a CMOS integrated 
circuit part number 4050, and the transistors 60 are included in a single 
integrated circuit such as RCA Corp. part number CA3724G. The transistors 
in the circuit 59 are connected as a Darlington pair to achieve sufficient 
power gain for switching up to a maximum rated current of 1 ampere. A 
single transistor could source up to about 100 milliamperes. Since the 
diode matrix 24 is scanned row-by-row and there are 16 rows, the maximum 
average lighting current to a single light-emitting diode in response to 
the multiplexer 57 alone is only about 80 milliamperes. To avoid this 
current limitation, the duty cycle of the switch 59 is increased to more 
than 90% by a dynamic memory capacitor 61 having a value of about 0.01 
microfarads. 
The driver integrated circuit 59 includes a first driver 61 for sourcing 
current to the transistors 60. The driver integrated circuit 59 also 
provides drivers 62, 63 for sinking as well as sourcing current. In order 
to achieve an extremely low leakage current, a silicon directional diode 
64 is placed in series with the current limiting resistor 31 so as to 
provide a high resistance path to block the flow of leakage current to the 
light-emitting diode 25 when the transistors 60 are turned off. Therefore, 
the leakage current is sinked to ground by the drivers 62 and 63. It is 
important to have low leakage currents because the the light-emitting 
diode 25, even in the strongest surrounding illumination, will have a 
photo-current on the order of one or more microamperes. The total current 
I.sub.y fed to the current-to-voltage converter 35 includes both the 
photo-current of the light-emitting diode 25 and any leakage current from 
the switch 32 which passes through the directional diode 64. Therefore, a 
very low leakage current is necessary so that the photo-current is not 
overwhelmed by the leakage current. 
The value of the current limiting resistor 31 is selected taking into 
account the voltage drop across the transistors 60, the directional diode 
64 and the light-emitting diode 25 when the light-emitting diode is 
illuminated. For a 5 volt lighting voltage, for example, the resistor 31 
should have a value of 10 ohms to provide a lighting current of about 250 
milliamperes. 
The photo-current switches 34 are provided by a second analogue multiplexer 
65. The second analogue multiplexer is again a 16 channel multiplexer, 
standard CMOS part no. 4067. For each light-emitting diode 25, the 
photo-current I.sub.y is received during the phase immediately preceding 
the phase for which the first multiplexer 57 refreshes the dynamic memory 
capacitor 61. In other words, if z denotes the analogue channel from the 
first multiplexer 57 for a particular light-emitting diode 25, then the 
photo-current I.sub.y is received on the z minus 1, modulo 16, analogue 
channel of the second multiplexer 65. 
To temporarily inhibit the lighting current for each light-emitting diode 
25 when the diode's photo-current I.sub.y is fed to the current-to-voltage 
converter 35, a third multiplexer 66 is provided to discharge the dynamic 
memory capacitor 61 so that the switching transistors 60 disconnect the 
light-emitting diode 25 from the lighting voltage U.sub.b when the 
multiplexer 65 selects the photo-current I.sub.y. It is further desirable 
for the multiplexer 65 to be inhibited until sufficient time has passed 
for the transistors 60 to turn completly off. For this purpose, an inhibit 
signal is generated by a timing circuit including a resistor 66, a 
capacitor 67, and a NOR GATE 68. The resistor 66 has a value, for example, 
of 100 K ohms and the capacitor 67 has a value of 1000 picofarads to give 
an inhibit time of about 90 microseconds. The buffer 69 drives the inhibit 
input of the multiplexer 65, as well as the inhibit input of the 
multiplexer 57. During the time that the multiplexer 57 is inhibited, the 
microcomputer 50 updates the input to the multiplexer 57 for the row z 
newly selected by the clock circuit 40. 
It should be apparent that the inhibit signal is applied to the first and 
second multiplexers 57, 65 immediately prior to a change in the address 
from the clock circuit 40. When the clock circuit 40 generates a clock 
address of z minus 1, the multiplexer 66 discharges the dynamic memory 
capacitor 61 so as to turn off the lighting current from the transistors 
60, assuming, of course, that the light-emitting diode 25 had been 
illuminated. The inhibit signal continues for about 90 microseconds, so 
that the transistors are turned fully off. At the end of 90 microseconds, 
the multiplexer 65 is no longer inhibited and the current I.sub.y, 
including the photo-current and any leakage current, is applied to the 
current-to-voltage converter 35. During the 90 microsecond inhibit time, 
the voltage on the output 38 of the current-to-voltage converter 35 
approaches its zero value, so that the current-to-voltage converter 35 is 
ready to receive the photo-current from the newly addressed light-emitting 
diode 25. 
The current-to-voltage converter 35, therefore, has left approximately 2.4 
milliseconds with which to sample the photo-current. Preferably, the 
current-to-voltage converter 35 includes a negative feedback capacitor 70 
so that the response time of the current-to-voltage converter is increased 
to a substantial fraction of the 2.4 millisecond sample interval, so as to 
reject any high frequency noise received by the operational amplifier 36. 
It is desirable, however, that the time constant of the capacitor 70 and 
feedback resistor 37 is rather small compared to the 2.4 millisecond 
sample interval so that a relatively inexpensive successive approximation 
analogue-to-digital conversion may be performed by the microcomputer 50 
without also using a sample-and-hold circuit. The analogue-to-digital 
conversion takes place approximately 1.5 microseconds within the sample 
interval. Therefore, the current-to-voltage converter 36 should reach a 
stable value after this time, thereby requiring a time constant of 
approximately 200 microseconds. The operational amplifier 36 preferably is 
of the kind having a MOS/FET input such as RCA Corporation part no. 
CA3140. The value of the resistor 37 is selected in accordance with the 
photo-current producing ability of the light-emitting diode 25 and the 
expected level of ambient illumination. Even for the strongest ambient 
illumination, the photo-current from the light-emitting diode 25 will not 
exceed a few microamperes. Therefore, the resistor 37 should have a value 
on the order of one megohm. To obtain the 200 microsecond time constant 
for the one megohm resistor, the capacitor 70 should have a value of 200 
picofarads. A one megohm resistance provides a conversion factor of one 
millivolt of voltage for each nanoampere of photo-current. 
The output 38 of the current-to-voltage converter 35 is fed to a respective 
input k of a fourth multiplexer 71 used as an input selector to a 
successive-approximation analogue-to-digital converter circuit including a 
digital-to-analogue converter 72 and a high speed comparator 73. The 
multiplexer 71 is, for example, standard CMOS part no. 4067, the same as 
the other three multiplexers 57, 66 and 65. Due to the negative voltage 
provided by the current-to-voltage converter, the multiplexer 71, in 
contrast to the other logic components of the circuit in FIG. 5, should be 
operated between plus and minus supply voltage, with V.sub.DD at +V.sub.s, 
and V.sub.SS at -V.sub.s. The operational amplifier 36 as well as the high 
speed comparator 73 and digital-to-analogue converter 72 also operate with 
positive and negative supply voltages. The high speed comparator 73 is, 
for example, RCA part no. CA311, and the digital-to-analogue converter is 
Signetics Corp. part No. LMDAC08CN. The inputs and outputs of the 
microcomputer 50 are assumed to fall within zero to 5 volts. Therefore, a 
quad comparator 74, such as RCA part no. CA339, is used for level 
conversion to interface a second set of output lines OUT3 of the 
microcomputer 50 to the select input of the multiplexer 71. The quad 
comparator 74 uses pullup resistors 75, for example 10 K ohms, and a 
reference voltage divider generally designated 76 including two 10 K ohm 
resistors. The output of the high speed comparator 73 is similarly 
interfaced to a single bit input (SBI) of the microcomputer 50 via a 
voltage divider including two 10 -K-ohm resistors 77 and 78. 
The digital-to-analogue converter 72, part No. LDMAC08CN, is designed to 
interface directly to a third set of output lines OUT3 from the 
microcomputer 50, and also provides a negative voltage output. 
In order to select the diode matrix 24 (see FIGS. 1 and 2) for entering and 
displaying data for either a first or second one of the inking units 14, 
one of the single bit inputs receives a signal from a unit selector switch 
79. The switch 79 shunts the input to ground for a low logic level, and a 
pullup resistor 80 of 10-K-ohms provides the high logic level. 
The microcomputer 50 has a fourth set of output lines OUT4 for transmitting 
ink adjustment data to the printing machine 10 (see FIG. 1) over the cable 
12. For a short cable 12, it is convenient to transmit these data in 
parallel form including lines for designating a selected one of 16 levels, 
lines designating the ink slide (x) to be adjusted and a line U 
designating whether the adjustment is for the first or second of the 
inking units 14. These data are synchronized to a clock signal obtained 
via a buffer 81 driven by the oscillator 53. The buffers 58, 69 and 81 are 
all provided in the same integrated circuit, standard CMOS part no. 4050. 
The microcomputer 50 is synchronized to the oscillator 53 via the same 
clock signal being applied to the microcomputer's non-maskable interrupt 
input (NMI) 
The microcomputer 50 also has a reset switch 82 for initially setting the 
ink adjustments to predetermined values and for commanding the 
microcomputer 50 to read and store the level of ambient illumination 
surrounding each of the light-emitting diodes 25. These values of ambient 
illumination also take into account any leakage currents or offset 
voltages associated with each individual light-emitting diode. For the 
purpose of sensing covering of the light-emitting diodes, threshold levels 
are computed for each light-emitting diode so as to fall below the 
corresponding level of illumination. As is conventional, a power-on-reset 
circuit is also used including a capacitor 83, and resistors 84 and 85. 
The capacitor 83 is, for example, a one microfarad capacitor, the resistor 
84 has a value of 100 K ohms and the resistor 85 has a value of 220 ohms. 
Turning to the FIG. 6, there is shown a flowchart of the non-maskable 
interrupt procedure which is executed during each sample interval in 
response to a transition on the clock signal from the oscillator 53. So 
that the microcomputer 50 knows which row of the matrix 24 is being 
addressed, in the first step 90 an index counter Z is incremented in 
modulo-16 fashion. Specifically, the index Z is first incremented, and is 
then compared to 16. If the index Z exceeds 16, it is set to 1. Also, so 
that the index Z will never be outside the range of 1 to 16, the index Z 
is compared to 1 and if it is less than 1, it is set equal to 1. In step 
91, the capacitors 61 for an entire row of the matrix 24 are refreshed. 
The logic state of each individual bit is transmitted from the 
microcomputer 50 to the N multiplexers 57. In practice, the microcomputer 
50 is an 8 bit microcomputer so that step 91 is advantageously performed 
by outputting a number of bytes. The bits or bytes are obtained from an 
array OUT(Z,K) in the microcomputer's memory. The array OUT(Z,K) is set to 
certain values in step 98 as described below. 
In step 92, a second index counter X is incremented in modulo N fashion. 
This second index counter X is used to address an array LEV(X,U) of the 
displacement-set values for the N slides in both the first and second 
inking units 14 (see FIG. 1) as selected by the logical flag U. In step 
93, the logical flag U, the index X and the ink density set-value from the 
array LEV(X,U) is transmitted from the microcomputer's fourth set of 
output lines. From the fourth set of output lines, these signals travel 
via the cable 12 to the printing machine 10. 
A third index counter Y is used to address an array THRESH (Y, K) of 
threshold values, and another array F(Y,K) accumulating a number of times, 
up to a maximum of ten, that the surrounding illumination of each 
light-emitting diode falls below its corresponding threshold level. In 
step 94, this third index Y is incremented in modulo-16 fashion and is 
limited to fall within the range of 1 to 16. As should become evident 
below, the index Y is in effect the modulo-16 difference between the index 
Z and 1. 
In step 95, the single bit inputs C.sub.o and U are read by the 
microcomputer. The indices Z and Y are synchronized to the value of the 
binary counter 51 (see FIG. 5) by first comparing the carry-out C.sub.0 to 
0 in step 96, and if the carry-out C.sub.0 is equal to 0, then in step 97 
the value of the index Z is set to 16, and the value of the index Y is set 
to 15. 
So that the monitoring circuit 39 will not respond to "popcorn" noise or 
static discharges, the intensity of the illumination surrounding the 
light-emitting diode 25 must fall below the corresponding threshold on the 
average of ten times before the monitoring circuit 39 will conclude that 
the light-emitting diode has been covered for the entry of data. 
Specifically, for each of the N light-emitting diodes in each row, the 
received intensity, stored in an array IN(K) is compared to its respective 
threshold value in the array THRESH(Y,K). If the intensity falls below the 
corresponding threshold, then the value of a corresponding filter array 
F(Y,K) is incremented. Otherwise, the corresponding element in the filter 
array F(Y,K) is decremented. The value of the filter array is limited to 
between 1 and 10. If the value of the respective element in the filter 
array F(Y,K) reaches 10, then the entry of data is recognized by setting 
the corresponding element LEV(K,U) of the level array to the value of the 
third index Y. In other words, if the operator covers a chosen 
light-emitting diode, that covering will be interpreted as a command to 
set the set-point of the ink slide for the chosen column to a level or 
setvalue corresponding to the selected row of the matrix 24. The entry of 
this command is further indicated by generating or updating a bar graph 
display. 
To generate the bar graph display, the value of the corresponding element 
of the level array LEV(K,U) is compared to the value of the third index Y. 
If the value of Y is exceeded, then the corresponding light-emitting diode 
is turned on, which is performed by setting the corresponding element of 
the array OUT(Y,K) to 1. The array OUT(Y,K), in other words, is an image 
table of the logic states displayed by the light-emitting diodes 25. If 
the value of the corresponding element of the level array LEV(K,U) is less 
than the value of the third index Y, then the corresponding light-emitting 
diode should be turned off, which is performed by clearing the 
corresponding element in the array OUT(Y,K). 
During the time that steps 94 to 98 were being performed, the 
current-to-voltage converter 36 was sampling the photo-current from the 
light-emitting diode 25. At step 99 in the non-maskable interrupt 
procedure of FIG. 6, approximately 1.3 milliseconds should have elapsed 
since the time that the interrupt was triggered by the clock signal from 
the oscillator 53. At this point, the microcomputer 50 performs a 
successive approximation analogue-to-digital conversion of the voltage on 
the output 38 of each of the N current-to-voltage converters 35 which have 
been sampling the photo-current from each of the N light-emitting diodes 
25 in the Zth row of the light-emitting diode matrix 24. In order to 
convert the voltage from a selected one of the current-to-voltage 
converters 35, value of the index K is written to the second set of output 
lines OUT2 for the microcomputer 50 so that the multiplexer 71 selects the 
output 38 of the Kth current-to-voltage converter 35. Then a conventional 
successive-approximation conversion procedure is carried out by clearing 
the third set of output lines OUT3 feeding the digital-to-analogue 
converter 72, and then for each of the eight bits of the 
digital-to-analogue converter 72, starting with the most significant bit 
and proceeding to the least significant bit, setting the particular bit, 
waiting a sufficient period of time for the voltage comparison to occur, 
such as one or two execution cycles of the microcomputer 50, reading the 
value of the comparator received on one of the signal bit inputs (SBI), 
and if the logic state of the comparator 73 is high, then clearing that 
particular bit. It is assumed that the polarity of the digital-to-analogue 
converter 72 is such that as the bits become set, the output of the 
digital-to-analogue converter becomes more negative, so that the value on 
the third set of output lines will be proportional to the light intensity 
surrounding the corresponding light-emitting diode. Therefore, the final 
value on the third set of output lines OUT3 is stored in the respective 
Kth element of the light intensity array IN(A). The interrupt procedure is 
completed in step 100 by execution of a "Return From Interrupt" 
instruction. 
Turning now to FIG. 7, there is shown a flowchart of a reset procedure 
which is executed by the microcomputer 50 in response to activation of the 
reset switch 82 (see FIG. 5). In the first step 110, the level array 
LEV(I,U) is set to predetermined initial values. As shown, for example, 
all of the levels are initially set to a mid-range value of 8. 
Next, in step 111, intensity threshold values are determined for each of 
the light-emitting diodes 25 in the matrix 24. To eliminate noise, the 
threshold value is computed by a digital filter having a "time constant" 
of 8 intensity samples. To compute the threshold, a predetermined 
sensitivity SENS is subtracted from the corresponding intensity value 
IN(K). The digital filter is a first-order filter employing the factors of 
7/8 and 1/8. It should be noted that the microcomputer 50 need not perform 
multiplications and divisions; rather, the division of 1/8 is performed by 
logically right-shifting by three binary places and the multiplication by 
the factor of 7/8 is obtained by copying the original threshold value, 
logically right-shifting the threshold value by three binary places and 
subtracting the right-shifted value from the copied value. Although the 
digital filter has a "time constant" of eight samples, since upon reset 
the threshold array THRESH(Y,K) could have any set of initial values, the 
digital filter in step 111 is turned on for sixty-four scans of the matrix 
24 in order to obtain a stable final value. 
After the initial calculation in step 111, the threshold is updated in step 
112 over a much longer time constant of about 256 samples. So that the 
threshold will track the surrounding background illumination, regardless 
of whether the operator is entering data by covering the light-emitting 
diodes, the accumulation in the digital filter is inhibited in response to 
the measured intensity IN(K) being less than the corresponding threshold 
value THRESH(Y,K). 
In view of the above, a method and apparatus has been described of the kind 
having light-emitting diodes for a display of input data, in which any 
fall-off in the photo-current produced in the light-emitting diodes by 
surrounding illumination is detected and evaluated as an input signal. For 
manual data entry, for example, the operator covers a selected 
light-emitting diode with his finger tip causing the photo-current 
produced in a light-emitting diode to be interrupted, and the interruption 
in photo-current is detected by an electronic monitoring circuit. By using 
a microcomputer in the monitoring circuit, the light intensity threshold 
for each of the light-emitting diodes can be independently set and updated 
over time during operation of the apparatus. This adaptive adjustment of 
the threshold also compensates for any leakage currents or offsets in the 
circuitry. By using digital filtering techniques, the reliability of data 
entry is ensured. By using row and column addressing of the diode matrix, 
the microcomputer can service a large array of light-emitting diodes for 
the display and entry of data. Therefore, external input devices such as a 
light pen are unnecessary.