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Subject: Re: help me understand intercoms

Date: 06/09/00 at 3:25 AM
Posted by: Bill Lewis
E-mail: FS.consult@eudoramail.com
Message Posted:

In Reply to: help me understand intercoms posted by dave on 05/20/00 at 6:18 AM:


Your LM386 circuit is just a means of amplifying the levels from a microphone up to a speaker. This is a standard audio circuit.

The Intercom just adds switching, one end of the intercom is a speaker/mic (you can use the speaker as a mic) and the other end is a speaker/mic and the amplifier/power source.

What you need to work out is the switching, as a hint you will only usually have 2 cores going between the two intercoms (fig 8 pair).

so the Call button on the master needs to have sufficient poles to exchange the remote speaker/mic from the input to the output of the amplifier and conversley the master speaker/mic to the output and input of the amplifier such that only one is connected to the amp at any one time.

the default state is so that the remote station is linked to the master speaker, this way the remote unit only needs a push to make button to enable it as a microphone.

If you follow that and addd your own thoughts i am sure you will be able to resolve it.

The LM386 circuit itslef is simple and i am sure , if you havent already, that finding a shcematic will be asy. (hint - National data book).


Bill Lewis
Technical Director
First Strike Consultants Ltd

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