Home > GCSE Projects > Two Way Intercom
Modified: 18:18, 26 October 2013

Designed by Phil Townshend, bulit by Tom Woodford 2005


This circuit is a high gain amplifier designed to use the speaker as a microphone as well. Using 8 ohm speaker (66mm) the input is around 2mV. This is amplified by two transistor amplifiers and the low voltage TBA820M amplifier IC.

The volume is controlled by VR1. A preset was used in this case but wires can be attached for a potentiometer if required.

The master unit is usually set to receive and should be a DPDT push switch if possible. PB1 is a call switch, but you must press transmit also which will sound a tone of about 400Hz to the slave unit.

The master unit houses the PCB, battery and speaker along with the DPDT transmit/receive switch.
The Slave unit just houses a speaker. The control over the direction of speech is accomplished by the Master unit.


Below is the PCB layout.
Remember to check the size of the PCB when you print it out using the scale shown.
For a better quality print down load the pdf file.

PDF format
DRW format

Note these are to scale but not exact size.


A view of the Master enclosure. This was made by vacuum forming 2mm white polystyrene over a mould made from MDF and plasticine or modeling clay.
It was then painted using enamel paints. The quality of detail achieved was excellent!
The Slave enclosure was made in a similar way but not so big since it only has to house a speaker. Note the pattern of holes drilled for the speaker.
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