DTMF with AT2051

Allen wrote:
> CBFalconer <cbfalconer@yahoo.com> wrote:
> > Allen wrote:
> > >
> >  ... snip ...
> > >
> > > 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.
> >
> > 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.
> 
> 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.

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!