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.
We found this circuit in a publication from the 1970s. It produces intermittent clicks on a...
We found this circuit in a Philips documentation from 1969. It makes use of transistors of the...
This circuit was found in a 1999 English magazine, but can be easily assembled with BC548...