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Looking for Simple DTMF Decoder Relay Circuit...

Discussion in 'Electronic Basics' started by Ike, Dec 21, 2003.

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  1. Ike

    Ike Guest

    Hello All...

    I'm looking for a ultra-simple DTMF decoder circuit that could be used
    as follows:

    One or more decoder unit(s) "listen" to a common audio source (FRS
    radio channel, hard-wired speaker, etc.) for a specific DTMF digit (1
    through 12 or 1 through 16) and if any of the individual decoder units
    "hears" its selected digit, it activates a relay. If the circuit
    "hears" any other DTMF tones, it ignores them. The decoder circuit
    needs to be able to select (with a DIP switch) to which specific digit
    tone it will respond.

    This system would typically be deployed in the field as a single
    keypad-equipped DTMF encoder master control unit which would be able
    to control up to 16 of the described decoder units. The operator
    could press any of the buttons on the DTMF keypad (which would simply
    play the DTMF tones into the audio stream) to activate any of the 12
    or 16 remote replays in the decoder circuits which were "monitoring"
    the audio stream. Since there could be up to 16 decoder units, the
    decoder circuits need to be simple and cheap, and identical with
    selectable digit tones.

    I have looked through the EEC (Encyclopedia of Electronic Circuits) 1
    through 5 but I didn't see anything like this.

    Thanks in advance!
  2. Anand Dhuru

    Anand Dhuru Guest

  3. Paul Blitz

    Paul Blitz Guest

    I'm looking for a ultra-simple DTMF decoder circuit that could be used
    Typically the DTMF decoder chips give out (a) a 4-bit output and (b) a
    "digit detected".

    To get a "linear" output, you need some sort of "decoder" (74HC138 does 3:8,
    then use spare enable inputs to select whether to use first or last 8)
    enabled by the "digit detected" signal.

    That help?

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