DTMF Generator

[JPKNHTP]

-JPKNHTP

[jimandy]

This may be an off-the-wall suggestion, but do you have an old out-of-service dial up modem? I once used one driven by a Stamp MPU to simulate repetitive calls to a paging server for testing. Easy to interface through a serial port and the ascii codes are well documented.

[JPKNHTP]

-JPKNHTP

[philba]

I believe they are sent together. A simple test is to pick up the phone and hold different keys down. You will hear a single tone composed of two frequencies.

The decoder filters the low and high frequencies seperately and determines the row & column from them.

here's some PIC code that purports to do it. try googling for "PIC phone dialer" PIC PWM DTMF dialer

<small>[ December 15, 2005, 02:57 PM: Message edited by: philba ]</small>

[Chris Smith]

For 50 bucks you can purchase a "Personal Assistant" emergency dialer,... part #PA5800 from X-10. They have another model with a built in Burglar alarm, but the 50 buck job comes with a small pendant that can be hacked to go off by any means.

It comes with a dialer, tone or pulse, 10 second message on a digital recorder, and it dials up to four number sequentially and wont stop if an answering machine picks up, or the person at the other end pushes doesn’t push ZERO into thier phone. Zero stops the machine and it resets.

It goes in endless dialing circles and wont stop till some one of the four persons or numbers resets it remotely, or directly.

It has a alarm as well, and a battery memory back up that holds the message and phone number for up to 24 hours should the AC power fail.

You can even hack the dialer and tone generator and If you would like a broken one to play with contact me. Im sure I have one or two bad ones that have the dialer is still working.

[jimandy]

5V to RS232 can be done rather inexpensively with a single chip that generates the negative voltage internally. I think Maxim makes 'em. (a bit of alliteration there).

Pretty sure circuitry on the web abounds if you want to roll your own.

[Robert Reed]

JPK
Just to answer one of your questions. DTMF= Dual Tone Multi-Frequency. Each row across has the same frequency tone. Each column down has the same frequency tone. Thus any button pushed sends out two frequencys simultaneously. Seven basic frequencys in a 12 button keypad and eight basic frequencys for a 16 button key pad.

[Edd]

“I have found the frequencies for the columns and rows but cannot figure out if the tone is column + row or if both the column tone and row tone are sent together.”


The column and row tones are sent together.

I’m sure that you already have the frequencies but here they are again.
( But don’t ask me for the phone co’s “Blue Box” proprietary use frequencies)

http://www.commlinx.com.au/DTMF_frequencies.htm

E.G. digit 1 is a simultaneous /combinational 697 and 1209~ sine pair.


73's de Edd
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