two way simple very small telephone exchange

8/6/2019 Two Way Simple Very Small Telephone Exchange

http://slidepdf.com/reader/full/two-way-simple-very-small-telephone-exchange 1/13

Two way Simple Very Small Telephone Exchange



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 generatingthree type of deference voltages & 100 AC volt for rigging.

It doesnt provided a PCB pattern for the power supply unit. So aVero 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 regulator5.1000 uf 35 V

6.1000 uf 16 v

7.150 ma fuse & its 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 connectionson the controlling unit circuit diagram.

TN_SLIC_1 & TN_SLIC_2SD_SLIC_1 & SD_SLIC_2RG_SLIC_1 & RG_SLIC_2

One SLIC connections should be marked as,

1. TN_SLIC_12. 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 23. LED x 1

Capacitors ( 16 V )

1. 4.7 uf x 4



2. 22 pf x 2

R esistors

1. 10 K x 42. 4.7 K x 43. 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 arerequired for this project.



Download SLIC Circuit Diagram

Parts list :

Transistors

1.2SD667 x 12.2SC945 x 2

Diodes

1. 1N4007 x 42. 9 v zener x 3

3. 12 v zener x 14. LED x 1

Capacitors ( 16 V )

1. 47 uf x 1

2. 22 uf x 13. 220 uf x 1

Resistors



1. 10 K x 32. 47 K x 1

3. 470 x 14. 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



Download PCB Pattern

two way simple very small telephone exchange

Documents