This circuit uses a crystal phone and can be built with more modern transistors like the BC548. The original circuit is from a 1979 publication and is powered with only two AA or AAA batteries.
This source can supply currents up to 1 A. The circuit is from Motorola's 1993 Linear Interface ICs....
The presented circuit uses a window comparator to keep a relay activated only when the sensor is...
The SCR sector of this circuit can be powered by high voltage AC and instead of the LEDs we can...