Looking for Simple DTMF Decoder Relay Circuit...

[Ike]

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!

 

[Anand Dhuru]

Hi,

Take a look at http://www.boondog.com/\tutorials\dtmf\dtmf.htm and
http://electronicsworld.tripod.com/remotecontrolsimages/2.gif

Hope one of the two helps!

Regards,

Anand Dhuru

 

[Paul Blitz]

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.

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?


Paul