PC address decoder (CB20536E)

This TTL decoder circuit for PC ports was found in a document from 1992. The power supply can be PC's own circuit.

Power grid powered metronome (CB7289E)
This circuit from an old documentation includes the power supply for the 117 V power grid. It can be...
Voltage comparator oscillator (CB5972E)
The frequency of this circuit is approximately 1 Hz. Whenever the output is at low level, the LED...
Crystal Tester (CB3881E)
This circuit has been found in an old documentation and therefore uses a lamp as an indicator. In a...