This TTL decoder circuit for PC ports was found in a document from 1992. The power supply can be PC's own circuit.
This circuit came out in a 1983 English magazine, but it can be easily assembled today, as the...
Originally recommended to give a tone of transmission in equipment of the 60s (tubed) this circuit is...
Reversing the switching action, with the output going high when the input is low, can be done by...