This circuit was found in Ferranti's 1967 documentation. The circuit drives a 40 V relay, but it can be adapted to operate with sensitive lower voltage relays.
We found this heart rate sensor circuit in a Popular Electronics from the 90s. The placement of...
This circuit, found in an old magazine of the year 1968, uses a Power germanium transistor. This...
This project came out in an article of mine (Newton C. Braga) in the Popular Electronics magazine of...