This circuit is from a 1968 publication. Here we have several types of resistive sensors with individual adjustments triggering a single SCR. Power depends on the type of sound device to be triggered.
This automatic volume control for audio signals was found in American documentation from the 90s....
This electronic voltmeter circuit was found in a documentation from the 50's. The sensitivity is...
Found in a Popular Electronics from the 90s, this game can be seen in other configurations on this site. The...