This sequential circuit of LEDs was found in a Popular Electronics from the 90s. The circuit can be programmed and an adaptation consists of using optical couplers to drive power loads.
This crystal tester was found on a 90s Ham Radio. Transistors are commonly used. The circuit is for...
This simple digital circuit tester can work with TTL technology when powered by 5 V and with CMOS...
The integrated circuit used in this 80's application is very hard to find today. The circuit is of an...