This circuit makes use of an optical coupler to isolate the telephone line. The circuit is from 1970s documentation. The components admit equivalents.
This circuit is intended to maintain constant current in a heating element. This element must have...
The sensor of this circuit consists of two 1N4148 diodes connected in series. The accuracy of the...
In the original version of a 1968 publication, this circuit uses BC109 transistors. However, the...