Figure 7. Testing counters and LED drivers in Test 4.
Apply power and you should see two LED light spots running in sequence, one from
each counter. Check the counting sequence of the LEDs to make sure that you have
soldered the wiring properly. Vary VR1 to adjust counting speed.
Test 5: Complete system test
Disconnect power supply and install U3. You should now have all ICs installed. Apply
power and you should see only one LED light spot with each bank of LED taking turns
to turn on. This gives the illusion of only one rotating light spot on LED0 – LED19 even
though the two counters are working simultaneously. If you still see two light spots,
check Q1, Q2, R3 and R4.
If you press SW1, the light spot should stop for about 2 seconds and then resume
running. If counting is not stopped, check SW1, R1, R2 and C3. LED20 should be lit
when the counting is momentarily stopped. If not, check R5 and the signal path from U3
pin 1 to U6 pin 10. If the light spot stopped but resume counting too quickly, you might
have the polarity of C3 reversed or wrong value of R2.
Dial VR1 to the lowest speed. Verify that if the light spot lands on the wining position, it
will trigger the buzzer. Verify that all other positions will not trigger the buzzer.
