New User - Phone Isloation Project

Discussion in 'The Projects Forum' started by spydrop, Jun 6, 2014.

  1. spydrop

    Thread Starter New Member

    Jun 3, 2014
    5
    1
    Hello - I am new to your forum and I did do some searchin before asking. Not sure exactly how to search this question though.

    I would like to "De-latch" a "Self-Latched" DTDP realy being held closed by a latch cicuit going through one side of the Relay contacts.

    When the phone is hung up and the telephone line returns to -48VDC "ON-HOOK" state I need for the relay to de-latch, de-energize and open both contacts.

    The Off-Hook voltage is -20VDC but, goest up to -48VDC in ON-HOOK state (Phone is hung up).

    Let me know if I need to post additional information.
     
    Last edited: Jun 6, 2014
  2. inwo

    Well-Known Member

    Nov 7, 2013
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    You could use a voltage sensing relay or circuit, to open a contact in the latch circuit, when voltage changes.
    But then that's what you're asking.

    What latches the relay?
     
  3. spydrop

    Thread Starter New Member

    Jun 3, 2014
    5
    1
    Hi inwo - glad to see your reply to my question.

    The relay is closed by a non-contact inductive pickup that detects the 90VAC (USA) Ring voltage in my phone line.

    See Board Below that I have build and it does detect and provides ground for via a transistor circuit.

    The line is disconnected from the grid by the open relay prior to getting a call.

    <<<< Easy to build this circuit >>>
    Once the Relay is closed by the 90VAC ring pulse for 60 seconds and it is timed by a 555 timer cirucuit. The Relay is a DTDP 120VAC.

    <<< This is where I need assistance >>
    if a phone is answered within that 60 seconds the line voltage will go from -48VDC "ON-HOOK" to -20VDC "OFF-HOOK" and the Relay remains latched close.

    As soon as the phone is hung up the -48VDC causes the relay to open. (Zener Diode Cicuit & Transistor controlling ?)

    This Circuit is the Below PCB Board:
    (It is based on the next Non-Contact Ring Detector Circuit)
    [​IMG]

    [​IMG]

    My non-contact ring detection board that does work (adjust wire wraps - good to go)

    [​IMG]
     
  4. inwo

    Well-Known Member

    Nov 7, 2013
    2,435
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    If you can build that much, unlatching the relay seems trivial.

    Or must this be non-contact voltage sensing?
    If voltage sensing is down stream from relay, it will not load the telco line while in standby.

    Can you post a drawing of the relay and latching circuit?

    This circuit is all powered from 9V rather than telco?
     
  5. inwo

    Well-Known Member

    Nov 7, 2013
    2,435
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    Not really knowing your circuit!:confused:
    Ignoring telco impedance and ring voltage "off hook".
    Latch signal must remain until off-hook voltage goes below Z.
     
    Last edited: Jun 7, 2014
  6. spydrop

    Thread Starter New Member

    Jun 3, 2014
    5
    1
    moffy, I'll work up a drawing this evening of the circuit for latching.

    I can use contact telco voltage to power a de-latch circuit for the relay. However, it has to be a non-polarized circuit. Will spend many hours on this today and tomorrow to get closer to a workable solution.

    Thanks.
     
  7. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    5,435
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    Nice little modem module! :)

    Where is that from?
     
  8. spydrop

    Thread Starter New Member

    Jun 3, 2014
    5
    1
    The White board is a Cortex M3 Powered Mico-Controller with builtin 802g Wifi for $39 and its called the Spark Core. The darker board is mine and I call it a Phone Isolation Shield "PIS".

    Right the only thing the PIS does is to sense telephone line power and lights an LED. Its a work in progress.
     
    THE_RB likes this.
  9. inwo

    Well-Known Member

    Nov 7, 2013
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    Did you look at the diagram?

    There may be better ways to do it. Need to know if that's the function that you want.

    Your relay/555 diagram would be helpful.
     
    spydrop likes this.
  10. spydrop

    Thread Starter New Member

    Jun 3, 2014
    5
    1
    inwo, Yes - you are correct about better ways and with my limited skills I am seeking suggestions. Current Sensing VDC is going to be difficult at 20 - 50mA. I have come the conclusion I need to get 3 different voltages directly from the phone wire and it shouldn't be a problem as I am going to design this for VOIP Application (Different Rules) and have 3 POTS that can be adjusted for backward compatability with Land Line Phone System (North America).

    What would you suggest for a circut to convert the 3 voltages to Analog signals for my Sprak Core MCU ?

    0 - 90VAC (RING)--- Bridge Rectifier ---> Opto Isolation, say a 4N25 or 4N28 --> ?? --> Analog Signal 0-3VDC. MCU Analog Pin 1

    6VDC - 48VDC --> 4N28 --> ? --> Analog Signal 0 - 3VDC . MCU Analog Pin 2

    Thanks for your help. Bobby
     
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