This circuit works with the previous two by demodulating the signals received modulated in FM. The circuit is from the Radio Electronics magazine of December 1992.
We found this circuit in factory documentation from the 70s. The operational amplifier is from...
This circuit for powering TTL and even modern microcontrollers is from February 1987, Radio...
We found this touch switch in a Popular Electronics from the 80's. The circuit can also be...