Published in a PE Hobbyst Handbook of 1991, this sensor uses an integrated circuit that is unusual today. The circuit is based on a high frequency oscillator.
I got this circuit from an English magazine from 1977. It can still be easily assembled, as the...
The configuration shown allows to obtain a high voltage gain for FETs. FETs can be BF245 or...
This circuit controls a heating element using a triac. Triac must be fitted with a heat sink. We...