This circuit makes use of an optical coupler to isolate the telephone line. The circuit is from 1970s documentation. The components admit equivalents.
Found in an Electronic Design from the 90's, this circuit uses common components. The circuit is...
When the sensor receives light, the relay closes its contacts and remains so even after the light...
This circuit produces pulses of 90 V at intervals that can reach 5 minutes. The circuit is from a...