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Capstone Project: DTMF Decoder

wrathofnero

Nov 10, 2009
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Nov 10, 2009
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In using a DTMF decoder, I hope to be able to use the 12 buttons of a telephone to turn on and off 12 appliances. We have the decoding schematic mapped out perfectly, but the question I have is about the phone we're to use. We don't have a phoneline. So, how can we power up the phone and also have it wired into the board? OR, if we use a computer, can we just splice an 1/8" cable and put the + and - in their designated spots out of the sound card with a digital DTMF keypad?

Thank you.
 

Resqueline

Jul 31, 2009
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Jul 31, 2009
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Just use any power supply (9-12-24V or thereabouts), hook it in series with a resistor (to give a fairly suitable working voltage/current to the phone. Then pick out the signal from the phone (junction resistor-phone) via a small capacitor and feed it to the decoder.
I forget the line voltage/current/impedance but they are fairly standard around the world and can surely be found on the net somewhere.
I'm sorry but I don't quite understand your last sentence.
 
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