This circuit detects when an audio signal exceeds a certain level or even occurs due to an object falling, a door slamming or other. The circuit is from a Radio Electronics from January 1980.
This simple strobe light is from an article in 1982. Its complete circuit, very simple, appears in the...
This power step for relay activation was found in the 1964 RCA transistors manual. The circuit is of the...
This circuit, bridge type, was found in American documentation from the 60's. The transistor is...