Separating Dc Current and voice Signal

[waqar]

Hi all,
I want to know what is the formula or theory behind separating voice signals and DC current ...

in many circuits there are transformer are used to create separation between current and signals and there are capacitor also doing this JOb...

How we know that this capacitor or transformer can do our JOb of separating current and voice signals...

Actually this question is related with my Door Intercom project

as i indicated earlier on this forum that i have designed a full duplex door intercom which require 4 wires from DOOR PLATE to House Intercom , the house intercom is a handset based intercom while door plate is a handfree intercom containing a bell button , condenser MIC and 8 ohms speaker.

On both sides i have used LM386 , and on handset side i have used also KA2410 ringer IC and the power supply is provided at the house intercom side 18 volts DC. ring occur at 18 volts while conversation take place at 9 volts....

Now in market there are full duplex door intercom which works on 2 wires , they contain transistor coupling amplifier and isolation transformer circuits but i don't want to copy that one as there out put sound is very low as in case of KOCOM door intercom products...

Now some how i want to convert my 4 wire intercom to work on two wires...any idea how to do this like sparating signals ?
using some transistor cirucit in between ?
or providing some transformer for isolating etc..?

actually i want to use LM386 to make 2 wire intercom which is also a full duplex one...

 

[mstechca]

You can convert it to 0 wires using radio technology if you use two different rooms. If there is a direct line of sight between the intercoms, you can try infrared technology. Otherwise, you could convert the audio into binary data, feed it along one line and convert the result into audio. (one binary line + one binary line = 2 lines)

 

[waqar]

eays to say binary = 2 wires

hi,
firstly thanks for the reply but its realy easy to use theorical words but to make it practical its realy a different thing....

can you jus tell me that what components can use to make this door intercom using LM386 , KA2410 for bell , so that full duplex conservation and 2 wires...

or what u suggest any components of deigning this...

Some one also suggested me the following this can any one help me on this:-

different approach would be to use a carrier system. The audio from each microphone would be used to modulate an RF oscillator (See the AM band transmitter in techlib.com, for example.) and the speaker at each end would be driven by a receiver that is tuned to the far transmitter's frequency. Each transmitter would be at a different frequency (say 1 MHz and 1.65 MHz, since I could supply the two crystals!) The DC power to run everything could be isolated from the RF by using ordinary inductors. This "carrier current" approach is used in intercoms that use the house wiring for the conductors so it should work quite well with dedicated conductors. The receivers could be inexpensive AM radios. It isn't a trivial project!