2B-Super Cheap Intercom




This project is very useful simple and cheap intercom.  Through this project you can communicate within your house or godown and send your message.  You can also listen the talk at that place.


Technical Description & Working System

This project has been developed and tested in our TV Engineering Technical LAB.  The component and PCB used in the projects published in our books are available for sale.  You can send your order giving the project code number.   The information about project code is given in the beginning and end of the book.  You can give you order through telephone.


Through this project you can contact a person sitting in a room of your house and you can know the position by talking to that person.  This project is made in a simple way with the audio amplifier section of a radio.


This project can be fitted in a radio cabinet.   Connect the DPDT switch and both speakers through wire.  When you keep the switch at TALK position, you can send your message in another room or at another place.  By keeping the switch in LISTEN position you can get the reply from another person sitting in room.


In the circuit 2 NPN transistors Q1 and Q2 [ BEL188 ] and transistors Q3 [ BC548B ] is used in the sound section.  In one room an amplifier with speaker and DPDT switch is kept.  In another room a speaker is connected through wire.  Only one coil is used from the two coils of secondary of transformer T1 in this circuit.  The signal at the primary of the transformer is given to the base of transistor Q3 [BC548B] through condenser C3 [0.01mfd].  The amplified signal available at the collector of this transistor goes to the primary of transformer T2 and is available at the secondary of transformer.

Through the secondary coils of driver transformer T2 goes to the base of transistor Q1 and Q2 [ BEL188 x 2 ].  The output signal available at the joint point of collector

of transistor Q1 [ BEL188] and emitter of transistor Q2 [ BEL188 ] is given to the speaker.  The DC supply to the base of transistors is given through the potential divider made of resistances R1, R2, R3 and R4.  The circuit is operated with 6V DC supply.


Precaution While Making the Project.


  1. Take care while selecting TALK / LISTEN position with DPDT switch 2. Connect the collector, Base and Emitter of transistor properly. 3. Check the parts before soldering them in the circuit.