Originally suitable for photography applications, this circuit from a Popular Electronics from the 90s can also be used to time plate baths. The components are common, and the sensor is remote.
White noise applied to an audio amplifier can be used as a relaxant, since it resembles the noise...
This circuit fires a xenon lamp being powered by a 300 V battery. The circuit is from a Radio...
The operational amplifier of this circuit is not very common today, because we removed the circuit...