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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