This circuit was found in the March 1984 issue of Radio Electronics magazine. The sensor is a transistor. The module is a common type at the time.
This circuit shows how we can take advantage of two old phones in a simple communication system. The...
In the figure we have two simple configurations of voltage doublers. Resistors and diodes are...
We found this circuit in an American 1980s documentation. The circuit can be assembled with modern...