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'[EE]:Telephone Dialer'
2001\12\13@020335 by Tim McDonough

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Has anyone been involved with circuits to take a phone line off
hook and then dial a number on command from the micro? In
general, the parts I'm still researching are:

- Detect if the phone line is already in use without disturbing
an in-progress call
- Go off-hook and dial a number (suggestions for the tone
generation part?)

The device/phone line connection should be a pre-approved DAA. We
don't want to jump through all those hoops ourselves unless
there's a big cost savings at the end.

Low cost is very important. I'm trying to avoid having to
purchase any of the available OEM modem modules or the stand
alone dialers that I've found so far.

A modem built up from the Silicon Labs Si2400 chipset runs around
$21-$27. The Cermetek modem modules are around $35. We don't
really need a true modem for the information we need to send. It
seems like it should be possible to do a much simpler dialer for
half to two-thirds of those costs.

Thanks for any reasonable suggestions,

Tim

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2001\12\13@021959 by David VanHorn

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At 12:54 AM 12/13/01 -0600, Tim McDonough wrote:
>Has anyone been involved with circuits to take a phone line off
>hook and then dial a number on command from the micro? In
>general, the parts I'm still researching are:

Been there, done that, in spades.

>- Detect if the phone line is already in use without disturbing
>an in-progress call

Can be done by detecting the line voltage, using a sampling technique.
Not 100% reliable, short CO loops and high resistance equipment cause false
"free line" indications unless you add multiple threshold selection

>- Go off-hook and dial a number (suggestions for the tone
>generation part?)

Easy, Holtek chips, or PWM it.

>The device/phone line connection should be a pre-approved DAA. We
>don't want to jump through all those hoops ourselves unless
>there's a big cost savings at the end.

There is, if you're doing more than a few.
The DAA guys promote the "scaaaary part 68" bit, but it's not that bad.

>Low cost is very important. I'm trying to avoid having to
>purchase any of the available OEM modem modules or the stand
>alone dialers that I've found so far.

See above

>A modem built up from the Silicon Labs Si2400 chipset runs around
>$21-$27. The Cermetek modem modules are around $35. We don't
>really need a true modem for the information we need to send. It
>seems like it should be possible to do a much simpler dialer for
>half to two-thirds of those costs.

You can also send DTMF faster than you think, but I do this sort of stuff
for a living.

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2001\12\13@053147 by Vasile Surducan

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I saw an interesting page about this subject:

http://www4.tpg.com.au/users/talking/TaxiPhonePage1.html



On Thu, 13 Dec 2001, Tim McDonough wrote:

{Quote hidden}

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