Two Way Simple Very Small Telephone Exchange

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Two way Simple Very Small Telephone Exchange 

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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 

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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. 

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Download Power Supply schematic 

Controlling Unit 

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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

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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

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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 

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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.

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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 

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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

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Download PCB Pattern 

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