All parts are available from mouser.com and similar
retailers. If the logic chips’ part numbers have additional letters appended at the end, this is acceptable.
Timer chips ( 3) Texas Instruments NE555P or
STMicroelectronics NE555N. Don’t substitute low-power, low-voltage CMOS versions.
Decade counter chip Texas Instruments CD4017BE
or STMicroelectronics HCF4017BEY
Counters with decoded output for 7-segment display
( 2) Texas Instruments CD4026BE
8-input OR/NOR gate Texas Instruments CD4078BE
Dual-digit 7-segment 10mm LED display Kingbright
DC04-11PBWA/A (blue) or DC04-11EWA (red)
Illuminated push buttons ( 5) E-Switch
LP4OA1PBBTR. Or use cheap tactile switches
such as Alps SKHHAKA010.
Tactile switches or SPST push buttons ( 2
for start and reset functions
LED for “game over” signal. Everlight HLMPK150
low-current red, or similar. Add 5 more if your
push buttons don’t have LEDs inside them.
Capacitors: 3.9nF or 0.0039μF ( 1), 0.01μF ( 3),
10μF ( 1), 47μF ( 1)
Resistors: 390Ω ( 1), 1kΩ ( 2), 1.5kΩ ( 15), 10kΩ ( 8),
22kΩ ( 1), 1MΩ ( 1)
Photoresistor approximately 50kΩ in average room
lighting. Often referred to as “photocells,” these
are becoming uncommon. Check eBay!
9-volt battery and battery clip such as Jameco
9-volt voltage regulator (optional) Fairchild
Breadboards ( 3) and jumper wire
I’ll use a 4026 CMOS chip for the Score Counter,
because it can power 7-segment numeric displays
directly. For compatibility, all the other chips should
be CMOS, too. They’re somewhat archaic now, but
that’s what you get, here in the Old School Version
of Zap-a-Mole. And since old CMOS chips are tolerant of a wide voltage range, I can power the Flash
Counter directly from the Game Timer, and run
everything with a 9-volt battery.
Diagrams and photography by Charles Platt
And to make the Burst Counter run for a truly
random time interval, I can adjust its duration with a
photoresistor that changes its resistance slightly in
Putting It Together
The schematics in Figures B and C (on the following
pages) are laid out like a breadboard version of the
circuit, shown in Figure D. It’s simpler than it looks.
I like to cut every little piece of wire to the exact length,
but if you’re less obsessive than I am and use pre-cut
wire, you can finish the job in less than 2 hours.
Start by wiring the scoring section (Figure C).
Connect the pin labeled 1a on the counter to 1a on
Game Timer activates
other chips to set the
duration of the game.
Flash Timer receives a
reset signal from the
Burst Timer, and starts
sending rapid pulses to
the Flash Counter.
Flash Counter counts
pulses from the Flash
Timer. It stops when
the pulses stop.
Player presses a
button. If it matches
the lit LED, a high signal
goes to the NOR gate.
NOR gate has a
normally high output,
but high input(s) will
drive its output low.
Burst Timer receives
a low signal from the
NOR gate. This flips its
output from low to
high. The length of this
pulse is randomized by
a photoresistor. The
pulse runs the Flash
Timer briefly, and
advances the score.
Score Counter (units)
Score Counter (tens)
Fig. A: This block diagram shows how the components