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Does anyone knows, how to send a command to microcontroller via handphone? For example turn on the relay, I press numeric one in my mobile phone. You don't have to be exactly right, any references will be appreciated.

How can I make the circuit (DTMF decoder) auto-pick up and receive command?

Please, take a look at following link, it might be helpful here.

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You need some kind of DTMF decoder. If your mico has a DSP core it would be pretty easy to do on chip. Otherwise you will need some external hardware to properly handle it. A quick google search turned up this project with an ATMega: http://www.uchobby.com/index.php/2007/09/30/phone-to-microcontroller-interfacing-with-dtmf/

Another issue is if the mobile phone will correctly pass DTMF tones. I don't see why they wouldn't, but its always a possibility.

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is it possible to send a command from phone ? for example press 1 to turn on my relay ? – Rick Ant Mar 23 '12 at 0:36
Indeed. When you press a button on your phone that DTMF tone would be transferred through the line to the speaker on the other side (thats how IVR systems work: en.wikipedia.org/wiki/Interactive_voice_response). A DTMF decoder could be connected to a micro, decode the tone, and then your application could trigger some other IO. – Kris Bahnsen Mar 23 '12 at 0:50
I believe all mobile systems will correctly send DTMF tones, however there might be issues with certain VOIP systems, I have no experience in that realm, but I know it is possible to have them not be properly sent: voipmechanic.com/dtmf-issues.htm – Kris Bahnsen Mar 23 '12 at 0:53
Which phone? Does it have a serial port? Would be much easier than detecting DTMF tones. – dext0rb Mar 23 '12 at 1:19
do you have example for DSP chip which can handle DTMF and controller ? – Rick Ant Mar 23 '12 at 2:44
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Are you sure that you want to do this using DTMF and DTMF only ? If short-messages (SMS's) are an option, or likely necessary then the DTMF route is unnecessary.

Unless your control circuitry is hooked up to your wired / fixed-line phone line, you'd need something called a GSM module to send/receive anything (voice, SMS...). Once you have such a module in place, you can interact between the module and your microcontroller using something called AT-command set. If DTMF is necessary in this situation, I am afraid your best bet may still be the dedicated DTMF decoders, and DSP route may be unnecessary or more complicated than it has to be.

If you do want to hit the DSP route, do check out Cortex-M4 microcontrollers, available from TI, Freescale, ST, NXP. Many of the silicon vendors might even supply DTMF detection library.

The advantage of the SMS route is that you do not need the DTMF detection capabilities.

BTW, DTMF detection can be done on a lot more lower-powered MCU, which do not require full FFT implementation but use some simplifications or alternative like Goertzel's algorithm, which are good enough for detecting presence of certain frequencies, as is the case with DTMF.

Find more information on the software (general MCU, non DSP) approach here: http://www.noah.org/dtmf/fft/embedded.html http://www.t-es-t.hu/download/microchip/an257a.pdf

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