I used a 8052 MCU (24MHz crystal) and a 8 bits R-2R DAC to generate DTMF tones.The sampling frequency is 5kHz. The output is then input to a 2nd order LP filter. The telephone line seems to not recognize my tone. Is the order of filter enough or not?
Thanks!
imaginabale cause
frequency error frequency compages error signal level oversize or lesssize of your output The sampling frequency up to 10kHz
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Or in other words, tell us enough to answer your question, and maybe someone will be able to help.
I would expect that nice sine waves fed to an 8-bit DAC with a sufficient sampling rate is more than good enough. Have you looked at your telephone line on an oscilloscope and compared your DTMF tones to what comes out of a regular telephone?
Apparently there is a bug in your generator. There is absolutely no necessity to generate nice and clean DTMF waves other then for the regulatory compliance.
Vladimir Vassilevsky DSP and Mixed Signal Design Consultant
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