This TTL circuit was found in an American documentation from the 80s. The components are common in the series and the supply must be made with a voltage of 5 V.
Found in a Popular Electronics from the 90's, this circuit detects the approach of objects by the...
This old 4-channel circuit was found in the December 1994 Electronics Now magazine. The circuit uses...
The figure shows how to implement an alarm buzzer in an LM3914 to warn about crossing the scale...