Searching \ for '[PIC]:Simple PIC Telecommunications' in subject line. ()
Make payments with PayPal - it's fast, free and secure! Help us get a faster server
FAQ page:
Search entire site for: 'Simple PIC Telecommunications'.

Exact match. Not showing close matches.
PICList Thread
'[PIC]:Simple PIC Telecommunications'
2001\09\29@113825 by Ken Boak

picon face
PIC Listers,

I have been experimenting with getting  PICs to talk to one another
over the public telephone network. The early trials of this are
proving to be successful.

I have a design for a PIC 16F84A based project, which I call the
Remote Access Terminal or RAT for short.

Using just an 'F84A, it can dial a DTMF number and send a V23 modem
message to another PIC.

The hardware to do this should cost less than $10.

All the DTMF generation and V23 modem tone synthesis is done in under
512 instructions - leaving another half kbytes for the user's
application programme.

A typical application would be remote datalogging or perhaps a device
to turn on your central heating remotely using just your mobile phone.

The hardware is flexible and the techniques are open to
experimentation using other processors  - the F628 and F877 would
make obvious good choices allowing more features than the humble F84.

I also have DTMF decoding an V23 decoding done in firmware running on
a 16F877.

The routines are free of charge to all those who wish to use them for their
own experimentation - all I ask is
feedback on how you get on.

The information is here:

Here you will find acces to the schematics, firmware, data and also a
discussion forum.

I hope that this is of interest.


-- hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

2001\09\29@122815 by Tom Messenger

>all I ask is
>feedback on how you get on.

Here's mine.

>The information is here:
>Here you will find acces to the schematics, firmware, data and also a
>discussion forum.

I went there but did not find the access to the schematics. Can you be more
specific? Thanks!

>I hope that this is of interest.

It is!

Best regards,
Tom M.

-- hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

2001\09\29@132846 by Ken Boak

picon face
Tom Messenger & Listers,

Thank you for your interest in my low cost PIC telecoms work.

In order to keep some form of document control, the schematics and other
files are only accessible once you have joined the Rat_Ring.

The Rat_Ring is an entirely free discussion group dealing with all aspects
of low cost PIC based telecoms.

To subscribe go to

and follow the instructions from there.

See you later on the Rat_Ring

Ken Boak

-- hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

2001\09\30@042132 by Ken Boak

picon face
Tom & Listers,

Thankyou for your interest in my DTMF dialling and V23 routines.

My initial brief was to get a 16C54 to work in an autodialler application,
and so the code is perhaps not as efficient as it could be - having to cope
with the lack of page 2 table reads on the C54, and other C54 limitations.
I only had a $3 component budget to work with, so it had to be kept simple.

I use the whole of the 8 bit B port to drive an R-2R resistor ladder network
as this costs about 2 cents. It allows a simple connection to the telephone
line using a single NPN transistor acting as an amplifying gyrator, and 2
high voltage transistors to form a hook switch. The whole lot was put on a
board and built for about $5.

The gyrator is key to the design, it is a single transistor circuit which
simulates an inductor ie it blocks ac from flowing but passes dc. They are
very useful in telecoms for powering equipment from the line - just 1
transistor and 4 passive components.

The routine for DTMF and tone generation started out as the one published by
Microchip in their application note. However I found that this was very poor
at the higher tone frequencies and just would not get through the telecom
approvals harmonics tests.

I went back to basics and rewrote it using aan algorithm with 2 moving
pointers which integer step their way through a 128 sample sinusoidal half
wave look-up table.  By varying the step size of the pointers it is possible
to generate the frequencies very accurately - within the +/- 1.5% required
for telecom DTMF.

The V23 routine also arose from this work and will send a V23 message to
line having dialled out using the DTMF routine.

I am now working on another routine to demodulate V23 tones  - again just
using a PIC16F84A  (minimum platform) and its meagre resources.  If I can
get this to work, a 16F84A could be used as a complete telecom modem for
simple projects requiring a telephone line connection.

This offers the possibilities of getting a WWW micro web server - based on
Dennis Petrov's implementation  and modem onto a cheap device like the

If you use a 16F628 you can send the DTMF samples to the PWM stage and save
all the B port lines for driving additional hardware.

You also have the means of putting a real time clock on a F628, and allowing
512 bytes for the telecoms routines, you have 3 times the application
codespace than was available on the F84.

If anyone has any good idea on V23 demodulation - I would be pleased to hear


Ken Boak

You can follow my work, and access all the code listings and schematics by
subscribing to the Rat_Ring discusssion group.

-- hint: The list server can filter out subtopics
(like ads or off topics) for you. See

'[PIC]:Simple PIC Telecommunications'
2001\10\01@083332 by Dan & Vijay Marchesani
picon face

Sounds like a GREAT idea.  I am going to take a look at it...  This is nice to
Comm with a HOME REMOTE DEVICE, or what ever you can dream up.  I will certain
like to have this circuit and Codes in my tool box of tricks..

Thanks for making available


Ken Boak wrote:

{Quote hidden}

-- hint: The PICList is archived three different
ways.  See for details.

More... (looser matching)
- Last day of these posts
- In 2001 , 2002 only
- Today
- New search...