Telephone : Checking for "RTS"

you could place a .1/600v cap between the A/B lines to your design. We use 1200bd signaling here but the signal sould pass in either case. And then you can use your existing power arrangement. Just make sure the caps are high voltage like 600v or 1kv. rw

oh, and google for "dtmf decoder", shows ideas for dtmf caller id. ew

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I don\'t know what you mean by the "A and B" lines, but if it\'s like
tip and ring is over here, why not connect the IRLEDs from two
optocouplers in anti-parallel and connect that set in series with
either A or B?

That way, one or the other of transistors associated with the IRLEDs
will be turned on and will give you polarity information while being
completely electrically isolated from the phone line.

Allready done. No enlightment came from any of the designs. They just receive DTMF, and only signal a "valid" when certain criterea to the reception of it have been met. None of them bother to check for polarity-reversal.

Regards, Rudy Wieser

John Fields schreef in berichtnieuws snipped-for-privacy@4ax.com...

Hello John,

Yes, the A and B lines are comparable to "tip" and "ring".

And alas, that method is only good when the phone has been picked up. I need to know what happens when the phone is still on-hook (before the phone rings for the first time)

Your suggestion is allready part of my design, so I know when the phone has been picked up (and tells my controller to interpret eventually incoming DTMF-signals differently).

Thanks for the suggestion though.

Regards, Rudy Wieser

meaning

phone

has

Something like this? -

Ken

Ken Taylor schreef in berichtnieuws jdd0g.13311$ snipped-for-privacy@news.xtra.co.nz...

Hello Ken,

Hmmm .... Looks like it could just do what I need (am not quite sure about the difference between the American phone-system and the Dutch one). Though it's a bit big (32 pin) and would mean I have to connect everything (including the DTMF-decoder and controller) directly to the phoneline ... I would have to think of another method to connect it to my computer (No path between the phoneline and ground may exist).

Thanks for the suggestion.

Regards, Rudy Wieser

about

Though

I

path

A telco isolation transformer at the input would solve your isolation requirements. As for the pin-count, yes it's probably excessive but it would do the trick and it also points toward other chips of its 'genre' which act similarly. There are other telephone IC manufacturers about so it's a matter of Googling the right keywords.

Cheers.

Ken

according to this:

and the included schematic, the dutch telecomm uses what we call a modem with a DAA to detect a loop reversal to get the DTMF signaling of the CID. Uses a Mitel/Marlink DTMF decoder. Quite a bit different from Bellcore. searched for "dutch caller id" rw

Ryan Weihl schreef in berichtnieuws e1vfdu$l5s$ snipped-for-privacy@emma.aioe.org...

Hello Ryan,

Thanks for the URL. And I did find that one myself too (I did spend quite some time searching for Dutch caller-ID stuff :-) ).

I'm not at all sure what you mean with "a modem and a DAA", (The only Modem-alike bit in the schematic is the max232, and isn't connected to the phone-line at all), but if you mean that the opto-coupler (ring-detector) could allso be used for detecting the line-reversal ... Well, maybe that could work.

I've thought about using it before, but I'm not at all sure about it's dependability.

Thanks for the hint/reminder though, I focussed so much on a 100% solution that I forgot this one :-\\

Regards, Rudy Wieser

P.s. A few things I have allways have wondered about when looking at this schematic :

1) What effect do those put into anti-series diodes D1 and D2 have ? Both together will not pass current in *any* way .... As far as I can see he (the designer) mixed up his zener-diode schematic (using an anti-series configuration) with a normal diode schematic (using an anti-parallel configuration)

2) why did the designer de-couple from the Phone-line with a trafo *and* capacitors etc. Why did he not just leave-out those capacitors ? Or even used the simple one-wire (plus ground) input ?

Ken Taylor schreef in berichtnieuws Sjo0g.13405$ snipped-for-privacy@news.xtra.co.nz...

Hello Ken,

Yes, but it would allso block any direct-current or voltage, which is, I think, needed by the chip for the reversion detection.

Although, it could just detect the voltage-spikes that are, on the other side of the trafo, the result of that line-reversal. Alas, dependability of the "has reversed" -signal would than be a bit questionable, as only the change-spike can be detected (no "if this volrage holds for at least ...mSec" -check can be performed).

Yep, that is what I did (did not find anything yet though).

Regards, Rudy Wieser

1) D1 and D2 are used to protect the ic inputs to 5V since you could get external noise spickes from the coupling transformer 2) this works like a dial-up modem, but instead of using a ringsignal it is using a voltage reversal to connect to the phoneline and receive the DTMF. The opto is used to detect the line reversal and uses the relay contect to present a 600ohm impedance to recv the signal. It also presents isolation btwn the unit and phone line. When the DTMF signal has been sent the polarity should reverse to the opto and drop the relay. rw

Ryan Weihl schreef in berichtnieuws e209vi$j3p$ snipped-for-privacy@emma.aioe.org...

Hello Ryan,

Could you pass that by me again, but that with a bit more detail ?

As far as I can see it those diodes *cannot* limit anything to 5V, as they are not wired like normal clamping-diodes normally are (and that should take

4 diodes, 2 for both lines).

I'm sorry, but I do not follow you here : "is using a voltage reversal" ? What part of the schematic might do that ?

I see. But only when the "phone" is allready Off-hook, and the relay has been activated (so the capacitor is bypassed).

As long as the relay is not activated it could be used as a ringing-detector, where it not that the output of that opto-coupler does not seem to reach the controller ...

Now I look more closely at it, I must say that that opto-coupler does not actually seem to be able to *do* anything, as it's output, pin 5, is going absolutily nowhere ...

It does however try to directly discharge a 47 uF capacitor, which could well lead to it being destroyed on the spot ....

I don't know what is going on here, but that schematic starts to look very funny to me. :-(

Please enlight me when I'm wrong.

Regards, Rudy Wieser

rudy referring to the schematic, Mitel is now Zarlink. I looked at this url

and they say the diodes should be 15v zeners used as frontend protection. We used 5.6v zeners (1n751) in similar arrangements for modem chips. I was involved in products like this, thats why I can talk about this. (now retired, but still like to keep involved). Can't find anything about the MT8060, but should be similar.

looking at the opto coupler and the loop. there is no current flowing thru the opto diode since the 6.8uF cap is in the circuit. But as soon as the polarity reverses in the loop you have current thru the opto, long enough to turn it on. This should fire the micro which turns on the relay. The relay contact shorts C1 (6.8uF) cap and you now have the opto turned on, keeping the relay on and the transfomer on the loop. Any DTMF tones will now be handled by the decoder. When the loop voltage gets reversed by the central office the opto turns off, the micro turns the relay off and the whole unit gets disconnect from the loop. Hope this helps. I know of some modem chips that decode DTMF tones (TDK) as well if the Zarlink part is out of range pricewise. We use bellcore specs here, and I built a few for us and friends. Had a LCD display and also stored the phone nbrs for about a month. The program was on a 8051, could retrieve the nbrs from memory, print them, etc. Normal caller id's can only display, but on this you could retreive and print. rw

rudy I think there is something missing on the schematic. Where is the output of the opto connected too? There is a 10k pullup on the opto, but no connection shown. Maybe we don't have to know everything. rw

Ryan Weihl schreef in berichtnieuws e216rn$9m1$ snipped-for-privacy@emma.aioe.org...

Hello Ryan,

As mentioned above, I can understand Zeners used that way. :-)

Hmmm .... Yes, I have thought about doing it the same way, but I find it bit tricky to rely on a single pulse as the line-reversal signal ... Oh, well, just one thing more to stay aware of while creating the controllers program.

I'm using the MT8870D myself, and it seems to work o.k. An older "C" version refused to work, and it took me some time before I became aware of the difference :-\\

Yep. That was what I was, among others, referring to.

Maybe it should have been connected to INT1 (pin7) on the controller. It's (still) free, and it looks logical enough to be able to be true.

Thanks for the help/explanation.

Regards, Rudy Wieser