This circuit was obtained in a Hobbyst Handbook from 1990. The circuit can be easily assembled since the SCR can be a TIC106 and the transistor a 2N30555.
We found this circuit in an American 1980s documentation. The operational ones used are not common...
This circuit has visual and audible status indication using an oscillator. The circuit is from a...
This bargraph-type circuit employs a not very common integrated circuit today, but can be adapted...