2-Way Telephone Exchange System

The project attaches two ordinary telephones to produce a fully bi-directional facility with an intercom system.

On it normal operation, the Exchange will detect and send ringing pulse to other phone when a phone is in off hook condition. The connection will be established between both phones when it is picked up which will take place in vice versa mode.

The telephone exchange system contains a power supply unit which uses a normal step down transformer with 400mA rating. This will generate the three types of deference voltages and 100VAC for the ringing. The power supply unit can be built using a vero board. Along with the transformer are the 2-bridged rectifiers, 5V & 12V regulators, capacitors, fuse & fuse holders, and the necessary wires & wire code for AC supply.

A PIC16F84A microcontroller is used as the basis for building this circuit. The controlling unit or Exchange is connected to 2 slimier SLIC. The other following connections may be identified on the controlling unit from the circuit diagram with other parts including the PIC16F84A with the firmware. The SLIC is required to detect every status from an unusual telephone set for the Exchange.

Rest of the project