This circuit was found in an 80's EDN. The circuit uses a current common CMOS, the 4093 powering an LED. Trigger adjustment is done in a trimpot.
This circuit, which can also be adapted to function as a microcontroller shield, is from 2003...
This sensitive circuit was found in an Electronics Hobbyists Handbook from the 1990s. The circuit can...
This circuit can be used with 3 receivers and is intended for low frequencies (medium wave range). We...