This simple audio and RF signal tracker was found in a Japanese publication in 1967. The transistors are made of germanium and the headphone is made of crystal.
This alarm circuit is from a 1990 Electronics Handbook. Transistor Q1 can be a BD135 and the relay...
This trigger circuit was found in old European documentation, but it can be implemented with...
This circuit is from the SGS Integrated Circuits Manual of 1982. The integrated circuit used is...