Found in a Philips publication from the 1970s, this circuit uses a DO040, which is difficult to obtain today. The circuit is powered by 12 V on pins indicated in the diagram.
This series sensor circuit is from 1995 Popular Electronics. The circuit can use any SCR and the...
The circuit is a multivibrator version using two NPN general purpose transistor. This circuit can...
This circuit is from 1976 documentation. It uses the operational amplifier 709 which is no longer...