This is the receiver from the previous alarm system. The circuit is from Radio Electronics, April 1989, and has an LDR as the sensor. Optical devices should be used to improve performance.
In the figure we have the way to increase the current capacity of an operational amplifier. The...
We found this circuit in a 1982 documentation, but the circuit can still be easily assembled, as the...
Found in an Electronics World of 1968 this circuit can use any SCR and diodes depending on the...