This alarm goes off if someone leaves a door open. We found it in the Encyclopedia of Electronic Circuits Volume 5 from 1995. The circuit uses components that are still common today.
We found this circuit in a 1995 publication. It makes use of infrared LEDs of the type existing at...
Relays up to 100 mA can be driven by the 555 with the recommended circuit. The circuit is from an...
The sensor for this circuit is a phototransistor. We found it in the April 1971 issue of Radio...