You know, DTMF is probably out of use now because it’s mainly used on analog wired telephones. When you press numbers to call someone on your grama’s telephone, you are basically making DTMF tones.
For those of you who want to mess around making your own spy gadgets, you might want to learn how to make a DTMF decoder. I really think that you would be far better off making a GSM-hack device of some sort that would be able to hack GSM signals. Well, just a thought.
At the very least, learning how to make DTMF decoder is one of the most basic circuitry you “should” learn if you don’t know how to already.
“The heart of this device is the MT8870, which is a DTMF to BCD decoder chip. It takes an analog audio input, and converts that to a 4-bit binary output. Those 4 bits are put into a BCD decoder, and that converts that into the corresponding 0-9 output. Various other devices were needed to complete the board, and can be seen in the board layout below.