KT3170 Vs. MT8870 DTMF Decoders

Discussion in 'General Electronics Chat' started by vinodquilon, Feb 13, 2010.

  1. vinodquilon

    Thread Starter Member

    Dec 24, 2009
    Does there exists any differences in the decoding response of KT3170/MT8870 DTMF Decoders ?.
    I am using MT8870 and have no capability to detect DTMF tones on on-hook state.
    But somewhere (http://electronicsworld.tripod.com/remotecontrolsimages/remotecontrolsckt2.html) I have read about KT3170 is that,
    Once a call is established (after hearing ring-back tone) on on-hook, if you dial ‘0’ in DTMF mode
    KT3170 can decodes this as 1010 without attending the call.

    If digit ‘0’ is not dialed (in DTMF) after establishing the call, the ring continues
    and the telephone connected in parallel can be used for normal conversation.

    If this is true I can simplify my DTMF project by replacing MT8870 with KT3170. In the case of MT8870 I have
    to design complex ring detection circuit to automatically off-hook.

    Many peoples obtained positive result by following the circuit in the above link using KT3170.
    My phone-set have no caller id facility. Does there any possibility for the caller ID (CLIP) signal to come ?
    Which mode is used to send caller information in India (FSK or DTMF). If it is DTMF, I think DTMF Decoders can detect DTMF tones on on-hook state.
  2. rogs

    Active Member

    Aug 28, 2009
    Not sure where you got the information from, but I think you'll find that the KT3170 is just a Samsung clone of the Zarlink MT8870.
    No differences, as far as I can see in the datasheets.

    I can't see why it would be so difficult to make a ringing current detector?

    There's a simple schematic here: http://www.epanorama.net/circuits/telephone_ringer.html about halfway down the page. Not a lot to it really!

    Simply detect the ringing current to seize the line, and use the opto-coupler output to latch the state with a bistable.
    Then use one of the DTMF codes to release the line (unlatch the bistable) when you've finished.