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 find this circuit in a 2005 Linear Technology manual. The circuit applies to small DC motors...
This 12V battery charging circuit automatically shuts off at the end of the charge. The disconnect...
This is one of many Morse code audio oscillators that can be found in this section. The circuit...