Hi,

Is the 2051 capable of generating DTMF like what is described in AN655
of the microchip Apnotes? If not, can someone recommend a cheap and
easily available chip that would be interfaced to the 2051?

I know I can get the DTMF dialer chip from a used telephone set but it
is normally for connecting to a numeric keypad instead of the data
lines of the cpu.

Thanks and regards.

Allen Bong

DTMF generation generally requires a lot of microcontroller resources, so it
really depends what else you require the micro to do whilst DTMF is being
generated. I usually prefer to use a seperate DTMF chip such as the Holtek
HT9201A. Yes, you need to simulate keypresses, but it really isn't that
difficult.

Ppelectron wrote:

I have modified PCB's from a phone to do the dialing with a 8051 micro.
Wire an opto accross a keypad, resistance is low enough when the opto
is on. Drive the opto's with the micro.
normally the keypad is arranged in a 4x4 matrix. A AT89C4051 has more
flash memory.

ppelectron@aol.com (Ppelectron) wrote in message news:<20040116175405.26403.00000103@mb-m07.aol.com>...

Thanks for your feedback. I am constructing a simple 5-zone home
security system under $50. The alarm detection will use interrupt.
Once the alarm is detected, it will run into a dtmf loop calling the
home owner handphone 10 times with 5 minutes break. There will not be
a dial tone detection and the dtmf tones will be sent after with 3
seconds delay after the phone loop. The Panic button would be done
using a SCR and a N/C button switch instead of a port pin.

I'd take a look at the datasheet of HT9201A as well as its
availablity. Have anyone used a PCD3311/3312 by Philips before?

Allen

"dont know" <mojo@nospam_netscape.com> wrote in message news:<2qiOb.89277$%wh.66518@news04.bloor.is.net.ca ble.rogers.com>...

I don't quite get it here. Are you wiring 'one' opto-coupler to the
keypad and send out decadic pulses OR are you wiring "seven" optos on
the column and row lines and on each digit, triggering two optos to
send out the dtmf tones.

I was thinking of using the line interfacing part of a modem for
experimenting with my DTMF sending.

Allen

ppelectron@aol.com (Ppelectron) wrote in message news:<20040116175405.26403.00000103@mb-m07.aol.com>...
I am building a 5-zone home alarm with dtmf sending if the alarm is
triggered. The zone detection is using interrupt and once triggered
the uC would call my handphone 10 times with 5 minutes-breaks. Dial
tone detection is not included and instead I've put a 3 seconds-delay
after off-hook.

The panic button is implememted in hardware using a SCR and a N/C
switch. I have been looking at the datasheet of PCD3311 by Philips
and can't find a dealer locally. Has anyone used this chip before?
I have also visited the Holtek website as you mentioned and they had
announced the discontiunation of the HT9201A chip. Now Holtek is
making some RC decoder and encoder chips using infra red and RF and
other more advanced microcontroller chips.

Allen

On 17 Jan 2004 16:56:52 -0800, sfbong@tm.net.my (Allen) wrote:


Have a look at:
http://products.zarlink.com/product_...index.htm#2810

for DTMF "transceivers" which can interface to a micro with 4 data
lines and a few control lines.

Alan


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P O Box 1108, Morley, WA, 6943
Tel: +61 8 9370 5533 Fax +61 8 9370 5106
Web Site: http://www.jenal.com
e-mail: http://www.jenal.com/contact.php
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Allen wrote:
If you are connected to the phone lines, why use DTMF at all?
Rotary dialing (pulse) still works. You may need some
configuration data for international use. Interface - one relay,
already needed for on/off hook.

--
Chuck F (cbfalconer@yahoo.com) (cbfalconer@worldnet.att.net)
Available for consulting/temporary embedded and systems.
<http://cbfalconer.home.att.net> USE worldnet address!

Allen wrote:

grab the line (VISTA 350) wire an opto across that as well and you
have a remote off-hock function.

CBFalconer <cbfalconer@yahoo.com> wrote in message news:<400A36FD.12480205@yahoo.com>...
Good points, I choose DTMF firstly I want to see how hard it is to
interface to DTMF stuffs. And if the project is successful, we might
market it locally. So DTMF is an important selling point and also its
ability to talk to PC via its serial port.

Nowadays it's hard to find a rotary type telephone ( I am still
keeping an NEC 8B phone for antique). Well, if I fail to do in DTMF,
decadic is a good alternative then.

Allen.

Allen wrote:
You don't need a rotary telephone - just pulse the line. The only
penalty is the aforementioned internationalization, and the time
to dial. You can't signal after connect, either.

Experiment - substitute atdp for atdt in your modem dialling
script. It should work, but may not be able to dial '#' and '*'.
Modem line control relays today are not large enough to handle the
inductive line surges, and may eventually weld themselves. I had
a Hayes that did that in about 6 months of use. You, being
prewarned, will not use the smallest possible relay.

--
Chuck F (cbfalconer@yahoo.com) (cbfalconer@worldnet.att.net)
Available for consulting/temporary embedded and systems.
<http://cbfalconer.home.att.net> USE worldnet address!