This LM380-based circuit was found in documentation from the 1980s. The components are current, and the transistor may be a general-purpose equivalent. Note the use of a medium impedance speaker.
We found this mains-powered switch circuit in Electronics Now magazine from July 1994. It could be...
This 80's circuit can be made with current comparators. Rectification accuracy is 1% DC up to 100...
When the light falling on the sensor is cut off, the SCR fires, powering the lamp. Remember that...