Detect busy tone and ring back tone

I have looked for IC's that would detect the various telephone signals, but have not found anything out there. Most of what I found are dedicated full function IC's that do it all for telephone use. These IC's don't output the signals, they are used interally - geared for telephone application. I don't think there is much need anymore for separate function IC's, which is a problem for guys like you & me. as a mater of fact the only chip I found that would detect DTMF was the now obsolete SS1202P. I was lucky enough to have one in my parts draw, and there is at least one web site that still has them. Obviously not a part you would want to use for a production design. The good news is that you can program a PIC chip to detect DTMF tones.

If I were doing it, I would probably use a PIC chip to detect the tones you are looking at. An eaisier way (if your not a PIC programmer) would be to use LM567 tone detecting IC's. The tones are dual tones that are switched on-off at a determined rate. You could AND gate two 567 outputs, and time the pulses to detect a valid signal. IE: "Precise" busy signal is 480HZ and 620 HZ @ -24dBmo per tone interupted 0.5 sec on, 0.5 sec off. Notice I specified "Precise" there is also "Modulated" busy signal which is 600/120 HZ. You need to find what is used by youre' exchange.

Ring back can be detected the same way, again there are several tone combinations out there. As far as detecting off-hook on the far end, I would just detect when the ring back stops. Good luck!

In the day, this was called "call progress detection", which may yield you some clues via google. For the so-called analog modems, the clock to the switched capacitor filter was changed to move the bandpass center frequency to specific places to do tone detection. There would be an energy detection circuit and some signal cadence analysis via the uP. I would say the short answer is the feature was hacked out of existing modem components since they were not needed until the call had progressed.

Here you go.

Bob

Nice! Wish I had that 6 months ago!

Yeah, I once played with some IC's from them. I think I used their tone generation IC's. Maybe the M-991? In any event, they were very simple to hook up and operate.

FWIW

Keith

Well, it's not "op amps and transistors"* but how about this:

It's an obsolete part but there are still a few available here and there...

Detecting supervision is a bit trickier. You may see a battery reversal when the called party picks up, but you can't count on it.

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Look for chipsets (and app. notes) for analog modems. They do this sor of stuff already. Just skip the data TX/RX functions.