This 1974 circuit uses two 555 integrated circuits in a very traditional configuration. The circuit can be powered by voltages from 9 to 12 V and for greater volume an amplifier stage can be added.
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...