This circuit is from the 80's, using an integrated of the time. The circuit serves as a reference, as this type of dialing is no longer used today.
The circuit presented may use any general purpose transistor. The indicator is an LED and...
This source was found in a 1982 American publication, but can be easily assembled using 2N2995 (PNP...
Found in a 1980s documentation, this circuit uses as base a component of the era. The formula for...