Found in a 1965 CQ magazine, this circuit uses period components. The unijunction transistor can be a 2N2646 and the relay has voltage according to the supply.
This circuit was found in the September 1974 issue of Radio Electronics magazine. The circuit uses...
This circuit was found in the December 1983 issue of Radio Electronics magazine. The sensor is an...
We found this circuit in a 1975 publication. The circuit can be made with more modern equivalent...