Nuts and Volts - September 2015

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.

Construction Suggestions:

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.