The transistors of this circuit found in a 1965 magazine can be the BC558 and the sensitive 12 V x 50 mA relay. The other components are common.
This circuit with LDR and neon lamp has its operating frequency given by the light. The circuit is from...
Found in American documentation from the 90s, this circuit can be used as a shield with the...
This tone recognizer circuit that relies on R5 and C1 was found in the December 1994 issue of...