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PICList Thread
'Telephone Dial logger.'
1998\01\19@222458 by mlist

I saw some questions a while back about using a PIC in generating signals
to send down a telephone line. My question is the opposite.

How do I use a PIC to monitor outgoing calls and log them out a serial

Has anyone done this in Australia for our Telephone system????

1998\01\20@090409 by Conor O'Rourke

> How do I use a PIC to monitor outgoing calls and log them out a serial
> port.
> Has anyone done this in Australia for our Telephone system????

I saw this done years and years ago in an ETI magazine. They were
using an 8051 or 8032 or something but the basics were the same.
Back then however, DTMF didn't exist (in the UK/Ireland) and
if I remember correctly, they had some sort of opto isolated link
to the phone line. They had a much easier job of it as they
could detect the break/make pattern of a dial out. DTMF will make
detection more work. If you really wanted to monitor calls properly,
you might want to check both pulse and tone dials.
Anyway, there's a great DTMF faq at:

Hope this helps a bit.


1998\01\20@113546 by )

There was an article (and kit) in an article by Terry Weeder in Nuts and
Volts Magazine within the past year that did just what you want (for US
phone system) and it used a PIC - 16C54 I think. The idea should be
applicable for any DTMF system. I don't remember if source code was
available. Sometimes his articles are merely paid kit instruction
articles. They sell back issues. Their web address is:

Hope this is of some help


1998\01\23@085607 by Keith Howell

I believe there was also an article on this kind of gadget
in Electronics Today International, (circa 1987?).
It caught my eye because I lived in a shared house,
with shared phone, at the time.

Not all residents had the patience, or honesty, to write
down their call details, so I hoped to catch the culprit out.

The ETI project had an 8751 and fitted within a standard
phone socket box. It stored data in some small non-volatile
memory which you could then dump to a centronics printer port.

You could make it prevent people from dialling high-cost
0891 phone-wank numbers, and other features.

As usual, you had to buy the expensive 8751 pre-programmed from
the designer, with no source code to check or modify.

It was some time ago, so I'm not sure if it worked with the
now ubiquitous DTMF phones.

If you do decide to do this project, consider getting it
to accept unique keys. It's all very well knowing which
numbers have been dialled, but nowadays you'll know that
eventually if you get an itemised bill. At the time, BT
didn't do this service.

What you really need to know is which one or more of your
housemates is responsible, and thus whose testicles to

I'd suggest you make the keys from Dallas Semi's "touch-id"
thingies. I've seen these used for tills in bars, where
they also have operator integrity problems.

I also suggest you make it with an infra-red RS232 link.
This is cheaper in I/O pins than a centronics printer port,
lower power, and opto-isolated as well.
I'd prefer to upload call logs than collect paper printouts.

Philips do some DTMF decoder chips.
I think one was used in Elektor's DTMF decoder project.

Keep me posted on your project.
What is its goals?

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