Hello
My goal is to create an application that recognises DTMF signals using a ARM7 uC (I have LPC2368). After looking over background theory (DFT) and after studying several code examples for different microcontrollers (msp, arm, pic...) I found an example made for LPC2138. I succesfully ported it to my board, but it doesn't work as expected. The program - as I understand - should work in a following way: DTMF signal should be connected on ADC and after a valid done is sent to ADC, correct number should appear in ie. Hyperterminal. The problem is: When I connect everything as it should be - and generate a DTMF signal trough my sound card using appropriate software which generated DTMF signals - i don't get correct results on ie. Hyperterminal. Furthermore the recognition doesn't work at all with standard DTMF tones however it partialy works with Knox (modified DTMF) frequencies. With Knox I get a respons in Hyperterminal, however the response is never correct - and for some DTMF buttons there is no response at all. For example when I press "1", I get "5" in Hyperterminal; when I press "2", I get "B" in Hyperterminal; when I press "4", I get "8" in Hyperterminal; and so on. When I press *,#,A,B,C,D I get no response at all.
Here is the link for the example I am talking about: http://www.keil.com/download/docs/325.asp
Does anyone have an advice what could be wrong? It seems very strange that the for example program recognises "1" as "5" always, not just sometimes...just like the frequencies in a DEFINE part if dtmf.c are mixed up - but as far as I checked they are not.