This project contains the details of using a Microchip PIC12F683 8 bit microprocessor to detect DTMF tones. The completed program allows the processor to be programmed with a string of DTMF tones to detect. If the programmed string is detected in the audio applied the audio input, the output will turn on (go high), and can be used to control other circuitry of the users design.
Due to requests for the source code, I have attached it. I have created a new step (Step 9) containing the *.asm file, along with some important notes.
The HEX file for progdramming that I originally attached to this instructable had a bug that prevented successful programing of the tone sequence, unless the microprocessor was in serial output mode while in programming mode. The HEX file attached now works properly. Sorry for any inconveniene caused for those who may have tried the original code.
I have included the *.hex file needed to program the microprocessor, 12F683_DTMF_DECODE_01A.HEX. You will need a programmer for PIC microprocessors. I have seen instructions on this site for building your own, but I cannot speak for any of them. The programmer I use came from a company called Micro Engineer Labs, Inc at www.melabs.com.
The only other parts needed are the electronic components, as shown in the schematic in step 3, Circuit Details. Digikey (www.digikey.com) is an excellent source for electronic components .
A telephone or other means of generating DTMF tones is also needed for programming the microprocessor with the the sequence of tones you want to detect. This is described in more detail in step 4.