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telephone circuits

Discussion in 'General Electronics Discussion' started by donkey, Apr 28, 2014.

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  1. donkey

    donkey

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    Feb 26, 2011
    hey people, I know there is an easier way to do this than I can think of so tell me, how can I make an intercom system with ringing phones?
    I am using it to replicate an EWIS setup for training purposes and am currently going with a 2 amplifiers to make life easy (but not cheap)
    I want to do a few things with this so please let me know
     
  2. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    Do you want to use telephone handsets? Or a loudspeaker that you talk into while pushing a button? Or do you want to use two standard wired or cordless telephones?

    What power sources are available at each end?

    How many wires do you want to use between the two ends?
     
  3. donkey

    donkey

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    Feb 26, 2011
    ok let me show you a few things, this way I can run through the idea in full
    [​IMG]

    ok so the row of buttons to the right of 1-6 are the WIP's. I want to pick up the receiver one end and call the receiver on the other. that receiver will ring until picked up then talking is established. when the button is pressed again I want the connection to be cut.
    however if they pick the phone up on the other end the little light will flash on this board and the phone will ring IF we aren't already on another call until we press the button and establish a line or they hang up.
    as this is for training I was going to have maybe 5metres between the "EWIS" and the "WIP" thus using 1 power supply of 12volts.
    I am currently in the process of making a system but am thinking it might be easier with old chorded phones, but then I need a 90vac supply at 20hz.
    I got to thinking about what a phone was and thought how about making my own cheaper. so have gotten a few awesome things of ebay to take control of the system. first I will use http://www.ebay.com.au/itm/14126485...e=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649this will be my naughty red phone. I designed a double ended circuit for the ringers and pick up thingy using 2 amplifiers for communication
    http://www.ebay.com.au/itm/141110093047?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649

    the ringers I will make myself. so at this point I will use about 6 wires.2 for speaker to mic, mic to speaker and the ringer circuit.
    I am then going to use another amp and speaker for the PA system, and then using 2 arduinos organise the actual alarm noises. so all up bout 500billion wires... or 10 if I am lucky.
    if you want drawings let me know and kris if you got me on chat still I can PM you further details. just let me know if you can think of an easier way.
     
  4. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    It sounds like you have it well in hand.

    One thing I can suggest is that POTS lines and phones use only two wires and pass audio in both directions. The carbon microphone and the earpiece are connected in series at each end; the two ends are connected in series, and DC (48V) with a series resistor is applied across the series circuit, causing current to flow. Each microphone varies its resistance in accordance with the sound it receives, and both earpieces reproduce the combined audio from both microphones. If you use this system, each end needs a carbon microphone (or a standard microphone driving a circuit that converts the signal into a varying resistance).

    If you run into any problems, ask here :) Good luck!
     
  5. donkey

    donkey

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    Feb 26, 2011
  6. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,271
    Nov 28, 2011
    I don't have much faith in that design. Let us know how it goes :)
     
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