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16 bit PCM bus - Notch filter / Tone detection

16 bit PCM bus - Notch filter / Tone detection

16 bit PCM bus - Notch filter / Tone detection

Hi All,

First time post so go easy :)

We have a HE910 telit module wtih a 16 bit PCM (DVI) audio bus that is normally connected to our SLIC interface.

I need to find a "quick and cheap" way to detect 1400Hz 100ms tone 2300Hz 100mS tones on the digital PCM bus. Im not after an actual design (unless you have one and want to sell it off cheap), just some ideas / direction would be appreciated

Option so far are
- Use a MAX9867 Audio codec to get "normal audio signals" then feed that into a couple of notch filters or some kind of ADC conversion and FFT...
- Use a DSP that has the codec (I think this will take to long to learn and set up)
- I can use my SLIC but its overkill, so I dont want to do that if I can help it.

RE: 16 bit PCM bus - Notch filter / Tone detection

Check out phase locked loops. There were some we used a loooOOOOng time ago that we set to the desired frequency. When they see that frequency they put out a "lock" signal.

Keith Cress
kcress - http://www.flaminsystems.com

RE: 16 bit PCM bus - Notch filter / Tone detection

Your 'Options so far' seem to be in the correct order.

You'll almost certainly need to convert the data into an audio spectrum, either 'actually' (your Option 1) or 'virtually' (your Option 2).

A variation on Option 2 (or 3?) might be a highly specialized FFT (just 2 narrow frequency bins) in processor software straight off the data. These days that probably wouldn't need a DSP. Two narrow frequency bins should be easy. And just enough temporal resolution to decide if it was 100ms or not.

RE: 16 bit PCM bus - Notch filter / Tone detection

Try the LM567 from Texas Instruments (originally NE567 from NXP/Philips, but I think it's obsolete).
This does exactly the job you want.



RE: 16 bit PCM bus - Notch filter / Tone detection

Thanks for the replies people. I also found out that the Telit HE910 cannot send DTMF tones during a call, so now I also need to transmit DTMF tones...

I have found a SLIC that has no DC/DC converter which I am getting a quote on ((should be cheap as there is no DC/DC interface), i hope the circuit is under USD$5 as I have this basically done already on a design that uses the SLIC. These things have DTMF encoders / decoders and programmable frequency detectors programmable oscillators.

I would have thought there would be PCM / DVI encoders / decoders with programmable frequency detectors for "diagnostics" or "modem tone detectors".

RE: 16 bit PCM bus - Notch filter / Tone detection

If you're looking for a DTMF decoder, stop leading us on a wild goose chase!
DTMF has a low range around 800 Hz and a high range around 1400 Hz.

The MT8870 will do the job.


RE: 16 bit PCM bus - Notch filter / Tone detection

DTMF tones (the standard ones) do not include 1400 and 2300 Hz.

This entire thread is a bit 'random'.

RE: 16 bit PCM bus - Notch filter / Tone detection

Obviously I am not looking for just DTMF as the first post clearly states, so there is nothing "random" and there is no "goose chase".

While talking to the engineers at Telit they confirmed that I cannot send voice channel DTMF tones from within the AT command set so not only do I now have to do 1400/2300hz tone detection, I also have to generate DTMF tones for transmitting. If you want to know why see here


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