Easy intercom 2 wire circuit


Posted on Apr 3, 2012

This Intercom is powered by two 9volt batteries and uses only current when the Intercom is used. Both units are connected via a two-wire little cable or simply two wires (dotted lines). The loud speakers act both as loudspeaker and as a microphone. When you press S1 and speak into the loudspeaker then this signal is amplified by the transistor stage and made audible in the right loudspeaker and vice-versa. An added benefit of this system is that when the switch is pressed it is quiet, not even annoying noise. This circuit has worked for me to my full satisfaction for many years now.


Easy intercom 2 wire circuit
Click here to download the full size of the above Circuit.

I get regular emails with complaints that there is no audio output when the button is pressed. As it turns out, the problem is always that a low-impedance loud speaker is used and although the circuit is working normally there is no audio or very little. Indeed it maybe difficult sometimes to obtain high-impedance loudspeakers, which probably is that by modern radio's the final audio stage is a transistor amplifier and they can provide a lot more current than a tube. To accommodate those in that situation, below is a solution which will solve the problem by using a audio transformer with a ration of 1:2 or 1:4 to 'up' the impedance. What that means is that the ohm's value at the primary side of this transformer is about 82 ohms. That will accomodate about 100mA max and because the collector voltage is pretty 'nil', it is impossible for the transistor to get hot. If it does, you have the incorrect transformer!




Leave Comment

characters left:

New Circuits

.

 


Popular Circuits

Scope-extender
simple mixer
the design of the intellectual wireless signal transducer of ARM
The E-meter
SLA7611M 3-Phase Stepper Motor Driver ICs
30W Power Audio Amplifier Circut
AT89C2051 Night Light Saver
Audio Resonant Equalizer Circuit Design
Hyper-Simple Battery Capacity Tester
50 impedance RF2320 linear amplification circuit diagram
Improve power supply rejection ratio PSR circuit diagram ISO124



Top