apart from home automation...i need some ideas which i can implement using dtmf concept...

 

Why use DTMF? Use caller ID circuits. Higher data rate, easier to modulate, and inexpensive.

Dan

 

How about using DTMF over RF to turn things on and off?

 

DTMF is slow, maybe you can get 10 codes a second... I might be on the low side here, butit is something I was looking into recently.

Caller ID signals are just an old fashioned 1200BPS modem link.

Dan

 

He asked for a DTMF project (other than a home phone line automation system).

I thought RF since no one has hear the tones as he sends them and I am sure someone has done that in the past (google.com maybe). Or an IR version. Just some carrier to ride the two tones over.

Caller ID/ANI or FSK is slow also and will work as well. I think he is looking for something to do with a DTMF generator for school. I might be wrong.

Also, slow is not an issue if you want to turn on one relay over an RF link.

My thought was he can make an FM transmitter and send DTMF, tune a FM radio and the teacher can hear it.. He is golden.

 

DTMF is good for any high noise low bandwidth data transfer application, any circuit that uses at least audio bandwidth frequencies could use it for some reason. I think FRS radio's in the US use a tone decoding (maybe not DTMF but at least related to it) as 'privacy' codes, basically a digitaly silenced squelch code. I don't think the FRS codes are in the audiable range but a decent decoding circuit could silence any DTMF tones and trigger various functions.

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Very common, even today, in the two way radio field to use DTMF to enable/disable link transmitters on repeater sites. DTMF pads are common on a lot of commercial two way radio's and are used for exactly these purposes. Another common use is to use DTMF over-dial on a touch tone phone to access such things as paging terminals, security systems, etc.
Yes, it's called CTCSS and DCS coding. Primitive but effective for eliminating unwanted signals being received but the 'privacy' word was just a marketing ploy used by Motorolla and others.

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That would work and I would not know what is used in those situations. I do know however that DTMF is a bit more complicated to generate and decode that simple the FSK that is used in caller ID, as well as being much slower.

Dan

 

i made project of home automation (turning electrical appliances on/off using dtmf concept through a phone call)..i just wanna add to these...like apart from home automation wat else can i control using the same thing...

 

Anything, skies the limit. Ever seen a movie called Back to the Future? The "Doc" has a Rube Goldeberg style setup that makes him breakfast in the morning and feeds the dog.

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