Found in a 1969s American documentation, this circuit uses transistors from that time. The configuration can be adapted to use modern equivalent components.
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...