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.
We found this circuit in a publication of 1990. With the changes it can be mounted easily today....
This simple photometer was found in a 1977 Radio Shack manual. The sensor is a photocell, which can...
This circuit is used to test a triac and also to teach how it works. The load is an incandescent...