This circuit for old analog telephones is from period documentation. It controls a relay that can be used to turn the extension on and off.
This ultrasonic insect repellent was found in American documentation from the 1980s. The...
We found this circuit in an English publication from 1980. It provides a logical output signal when...
We found this circuit in a 1977 Italian Elettronica Prática. BC107 can be replaced by BC547 and...