September 2015 81
realized at the gate output (assuming that the remaining
input to the AND gate is held high).
The contacts in each pushbutton are debounced
with a paralleled R-C network.
The 12 VDC power can be provided by a small
wallwart regulated power supply. Anything that will
provide 100 mA or more will suffice.
1. Note that the integrated circuit (IC) package
schematics show the two 4013B elements, the six
4049B elements, and the four 4081B elements, and that
each IC is bypassed by a 0.01 µF disk ceramic capacitor,
to be connected with the shortest possible leads across
the power input terminals of the IC.
2. Pin assignments in the circuit schematic are
illustrative; consult the IC package schematics for actual
pin-outs for each circuit element in any particular IC.
3. The tie-breaker circuit shows two 4049B elements
connected in parallel. Both elements must reside in the
same IC package.
4. Diodes are 1N914 or 1N4148 signal diodes. All
resistors are 1/4 watt carbon composition. With one
exception, the capacitors are all disk ceramic, of any
type (Z5U or better), 25 volts rating. The polarized
capacitor is tantalum, and is to be connected directly
across the 12V power input to the circuit board.
5. While the circuit schematic shows only three
“student receiver” circuits, there does not seem to
be any reasonable limit to the number that might be
included, so long as +12V, circuit ground, and the
+RESET and -INHIBIT busses are extended to all.
6. The input pins of all unused circuit elements must
be connected to ground.
7. The student switches should be connected to
the main console using twisted-pair cable to ensure
minimum noise sensitivity. Mount the R-C debounce
circuit directly across the pushbutton pins.
8. Dual-in-line package (DIP)-type ICs and IC sockets
Datasheets for the three ICs may be found at:
A 1N914 diode datasheet is located at:
Parts are all readily accessible from Digi-Key,
Mouser, Jones Associates, Newark, etc.
Peter A. Goodwin
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n FIGURE 1