Two way Simple Very Small Telephone Exchange

Summary of Two way Simple Very Small Telephone Exchange


This project describes a small bi-directional telephone exchange system connecting two ordinary telephones with intercom functionality. It uses a PIC16F84A microcontroller to detect when a phone is off-hook and sends a ringing pulse to the other. Upon answering, a connection is established for two-way communication. The system includes a power supply unit using a step-down transformer and voltage regulators. The controlling unit interfaces with two SLICs (Subscriber Line Interface Circuits) and includes transistors, diodes, capacitors, resistors, and a relay.

Parts used in the Two Way Simple Very Small Telephone Exchange:

  • PIC16F84A Microcontroller
  • Step down transformer (230 V to 30 V, 15 V & 100 V)
  • Two bridge rectifiers (1 A)
  • 7805 5V voltage regulator
  • 7812 12V voltage regulator
  • 1000 µF 35 V capacitor
  • 1000 µF 16 V capacitor
  • 150 mA fuse and its holder
  • Necessary wires and AC supply wire
  • Transistors 2SC945 x 3
  • Diodes 1N4007 x 1
  • Diodes 1N4148 x 2
  • LED x 1
  • Capacitors 4.7 µF (16 V) x 4
  • Capacitors 22 pF x 2
  • Resistors 10 KΩ x 4
  • Resistors 4.7 KΩ x 4
  • Resistors 330 Ω x 1
  • 12 V telephone relay x 1
  • Two SLIC modules

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

Two way Simple Very Small Telephone ExchangePower 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.

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.

Two way Simple Very Small Telephone Exchange SchematicParts 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

 

For more detail: Two way Simple Very Small Telephone Exchange


About The Author

Ibrar Ayyub

I am an experienced technical writer holding a Master's degree in computer science from BZU Multan, Pakistan University. With a background spanning various industries, particularly in home automation and engineering, I have honed my skills in crafting clear and concise content. Proficient in leveraging infographics and diagrams, I strive to simplify complex concepts for readers. My strength lies in thorough research and presenting information in a structured and logical format.

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