Re: Telephone : Checking for "RTS"

R.Wieser wrote:

Ryan Weihl <nixnam@xxxxxxxxxx> schreef in berichtnieuws
e209vi$j3p$1@xxxxxxxxxxxxxxxx

Hello Ryan,
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 ?

1) D1 and D2 are used to protect the ic inputs to 5V since you could
get external noise spickes from the coupling transformer

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).

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.

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

The opto is used to detect the line reversal

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
http://assets.zarlink.com/AN/msan_108.pdf 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


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