Communication circuit “Telephone”

When you hang up the line to hook the wires are switched to the tone, which is so ready to alert you to a call. As soon as you respond, lifting the handset, the wires are switched to the microphone circuit

Study of ‘equipment at our disposal

On two wooden panels had been made a circuit that allowed you to communicate through a microphone and a receiver was also a button to activate the buzzer to call the second unit.

Operation

Circuit voice: shown in the first figure. The user picking up the receiver closes the contacts when you speak into the microphone creates a signal in a closed loop (red in the drawing), thanks to the transformer (yellow) signal is transmitted into the receiver circuit (orange) and can be heard from ‘other end.

Circuit ringtone: shown in the second figure. Pressing the button on the right panel closes the circuit of the ring (green) that plays on the panel. When you lift the handset opens up the contact that disables your ringtone.

We children members of the Giovani per la scienza we studied the circuit of the phone and, after having understood the operation, to make the device working again we had available, it was necessary to replace some wires and one of the two microphones damaged by time and restore then the circuits.