This circuit triggers a buzzer or other warning device when the light falling on the sensor is cut off. We found it in the Encyclopedia of Electronic Circuits Volume 5 of 1995.
This stable 20 MHz oscillator was suggested by the National Semiconductor's Linear Applications Handbook...
This buffer and driver is from the integrated circuit manual itself, the Linear Technology LT1206. The...
The transistors in this 1978 circuit can be BC548 and 1N4148 diodes. The electrolytic capacitors can be...