Cell phone dtmf generator/decoder

[betwixt]

Did you try changing the speed parameters? For example AT+CKPD=1234567890,1,1 the last two numbers set the tone duration and the gap between them.

If that doesn't work I think the phone firmware will not do what you want. The dialer may be capable of sending fast enough but the AT command may have its own restrictions.

You could always make your own tones and send them over the voice channel.

Brian.

 

[khaldun904]

Thanks anyway you were very helpful:razz::smile:;-);-) .
what i will do that is my Luke nothing work good.
thanks a lot

 

[stas.za]

Hi i am currently working on something similar but i am having a slight problem getting any output from the dtmf. I do how ever get an output on pin 16 every time i press a key on my cellphone but no output on pin 11-15. Could the problem be the phone I'm using?

 

[betwixt]

It's unlikely to be a problem with the phone. Pin 16 goes high when the detector recognises valid tones so the audio and connections must be working. What do you have connected to pin 10 ? If it is driven low or tied to ground it will disable the data outputs, it should be left floating or idealy pulled to +V supply through a resistor of 10K or so.

Brian.

 

[stas.za]

It's unlikely to be a problem with the phone. Pin 16 goes high when the detector recognises valid tones so the audio and connections must be working. What do you have connected to pin 10 ? If it is driven low or tied to ground it will disable the data outputs, it should be left floating or idealy pulled to +V supply through a resistor of 10K or so.

Brian.

Thanks for the reply.My pin 10 was floating.i connected it to +5v as suggested but still no luck.Any ideas what could be wrong?

 

[sahin5002]

Hi betwixt . I need you attention. Its an emergency.
My problem is, I connect mt8870 with SIM300C GSM module and PIC18F2550 for reading DTMF output. Every thing is working fine but sometimes STD (pin15) of mt8870 blinking (LED connected) for several times for a single DTMF tone. My software always monitoring STD pin and read the new data. But for the blinking software read some false digit.
Then I take a delay (150ms) after each reading. IT decrease the false reading but still have.
How can I remove the blinking of STD pin.
My schematic

 

[ALERTLINKS]

The delayed steering (Std) output of the IC goes high on receiving the tone-pair, causing LED5 (connected to pin 15 of IC via resistor R15) to glow. It will be high for a duration depending on the values of capacitor and resistors at pins 16 and 17. Make differential Input for reduced noise and filter 5v supply with 1000uF capacitor.
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[betwixt]

Sorry for not replying earlier, I get several hundred emails a day and sometimes messages and postings here get lost in the backlog !

As ALERTLINKS states, the componnts between pins 16 and 17 are there to make the IC less sensitive to short tone bursts. Even though the pairs of tones used in DTMF are chosen because they rarely occur together in a human voice, there is still a small chance of false detections. Those components are there so the IC only reports the tones after they have been present for a certain time so brief sounds are not reported. If you increase the time constant of these parts you can prevent the multiple detections. Inside the IC, when the tones are detected, the "Est" (16) pin respnds immediately but the strobe and data pins are not updated until "ST/GT" (pin 17) reaches the same logic level. The diode is there to make the timing asymetric, a fast response when a digit is detected but a slower response before another one can be reported. The calculations for their values is in the data sheet.

Brian.

 

[ramza038]

Can someone kindly send me ur working ckt diagram. I urgently need for my final year project.