This circuit without sensors in series triggering an SCR was found in volume 5 of the 1995 Encyclopedia of Electronic Circuits. The circuit can have the number of sensors changed.
This SCR circuit activates a buzzer when triggered. The circuit is from a Popular Electronics from...
This circuit is used for incandescent lamps and other resistive loads up to 3A using the TIC206. This...
This circuit is from 1995 documentation, but can be easily assembled today, as the components used are...