Two way Simple Telephone Exchange

Tuesday, 27 October 2009 03:38 | Written by EEE-LAB |

This is a very small telephone exchange attached only two ordinary Tele phones. Fully bi-directional facility with an intercom system. When a phone is in off hook condition , Exchange will detect it & send ringing pulse to other phone. When it will be picked up , the connection will be established between both phones. This will be taken place vice-versa.

Micro Controller = PIC16F84A
Firmware version = 1.00
Power Supply = 230 v

Power Supply Unit

The Power Supply Unit.

This is used normal step down transformer (400ma) for generating three type of deference voltages & 100 AC volt for rigging.

It doesn�t provided a PCB pattern for the power supply unit. So a Vero board can be used to build the unit.

Parts List :

1.Step down transformer ( 230 V to 30 V , 15 V & 100 V )
2.Two bridged 1 A rectifiers
3.7805 � 5V regulator
4.7812 � 12V regulator
5.1000 uf � 35 V
6.1000 uf � 16 v
7.150 ma fuse & it�s holders.
8.Necessary Wires & a wire code for AC supply.

Download Power Supply schematic

Controlling Unit

The controlling unit ( Exchange )

This circuit is base on PIC16F84A microcontroller. Two slimier SLIC are connected to The controlling unit. It needs to identify following connections on the controlling unit circuit diagram.

TN_SLIC_1 & TN_SLIC_2
SD_SLIC_1 & SD_SLIC_2
RG_SLIC_1 & RG_SLIC_2

One SLIC connections should be marked as,

1. TN_SLIC_1
2. SD_SLIC_1
3. RG_SLIC_1

Other SLIC connections should be marked as,

1. TN_SLIC_2
2. SD_SLIC_2
3. RG_SLIC_2

These connections should be connected as on the controlling unit circuit diagram.

Download CPU Circuit Diagram

Parts List :

Transistors

1. 2SC945 x 3

Diodes

1. 1N4007 x 1
2. 1N4148 x 2
3. LED x 1

Capacitors ( 16 V )

1. 4.7 uf x 4
2. 22 pf x 2

Resistors

1. 10 K x 4
2. 4.7 K x 4
3. 330 x 1

Other Parts

12 V telephone rely x 1
Necessary wires
PIC16F84A with the firmware

SLIC

The SLIC (Subscriber Line Interface Circuit )

This unit is required to detect every status from an usual telephone set for the Controlling circuit ( Exchange ). It interfaces an usual telephone to the controlling circuit. Two slimier SLIC are required for this project.

Download SLIC Circuit Diagram

Parts list :

Transistors

1.2SD667 x 1
2.2SC945 x 2

Diodes

1. 1N4007 x 4
2. 9 v zener x 3
3. 12 v zener x 1
4. LED x 1

Capacitors ( 16 V )

1. 47 uf x 1
2. 22 uf x 1
3. 220 uf x 1

Resistors

1. 10 K x 3
2. 47 K x 1
3. 470 x 1
4. 100 x 2
5. 47 ( ½ w ) x 1
6. 5 (½ w ) x 2

Other Parts

RJ 11 telephone connector x 1
12 V telephone rely x 1
Necessary wires