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.
Found in American documentation from the 90s, this CMOS circuit detects the source of a signal and can...
I found this circuit in an old English magazine from 1981, but it can still be assembled with some...
This circuit was obtained from a 1969 Electronic Design. Transistors admit modern equivalents. The frequency...