This circuit reproduces the dial noise in a small speaker. The transistor can be a general-purpose type. We found it in an 80's Electronic Design.
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...