This interesting digital counter with relays with complementary outputs was found in the Radio Electronics magazine of October 1961. The supply voltage is in accordance with the relays used.
This 1968 Mullard circuit detects fire by smoke using LDR-type sensors. The circuit makes use of...
Found in the American 73 magazine for radio amateurs, this circuit can test common quartz...
With this circuit it is possible to tune the signals in the 50 MHz band in a common AM receiver around...