DTMF Tone Decoder

This project displays telephone numbers decoded from tones. A microphone picks up the tones, a preamplifier boosts the signals, an SSI-202 DTMF chip decodes the tones, a Basic Stamp acts as an interface to an LCD display and also provides "RS-232" serial output.

News Flash! I'm not going to design a PC board or release kits of
this project because someone else is making a reasonably priced DTMF
decoder with similar features, and should be making inexpensive
kits by now. Check out his web page: www.dschmidt.com/dtmf.html and see what his tone decoders are like. They look really good. If you'd like to buy a tone decoder, please don't write me.

If you'd like to build your own tone decoder "from scratch", read on:
You might have trouble finding the SSI-202 chip, even though Radio Shack used to sell them.
 In the United States, the best place to buy them in small quantities is B.G. Micro, www.bgmicro.com. They have the SSI-202 chip for $2.25.

If you have access to Mitel 8870 DTMF chips, you could use it in this circuit if you change the pins to match the corresponding functions. I have not done it, so I canít help you. Silicon Systems, maker of the SSI-202 chip, has been dissolved by Texas Instruments. B.G. Micro has made the data sheet available at http://www.bgmicro.com/proddoc.htm

The schematic diagram of this project. I have not included a parts list, but I've tried to make the diagram self-explanatory. If you can understand it, you can probably build it. Due to popular demand, I have included a modification that allows direct connection to the phone lines. I must say, however, that I have not tried the modification(I have been told it does work) and it's probably against the laws of certain countries, states, provinces, townships, and telephone companies to connect home-made devices to the phone lines.
 
The software for this project. It is only a bare-bones program. The smart people that build this circuit will surely write some better programs and send them to me to include in this page. This program works fine, it's just very basic. You must rename it with a .bas extension before loading it into a Basic Stamp.

 

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