How to interface MT8870 with SIM300c GSM Modem

[sakaz]

mt8870

Hello Forum,

I have been trying to work with the Sim300c gsm modem and finally i have done and it is really great to learn from this great forum. I have finalized everything but i can not read the DTMF tone from the gsm modem.

My decoder circuit with MT8870 single ended and working great with the dtmf taken from the mobile phone. Sim300c has two speaker output SPK1P SPK1N. so how i can interface the with the DTMF decorder. Could you please provide me any schematic or suggesion to work it. Because everything is already finazlied.

Best regards,
Shan

 

[phaedrus]

mt8870 circuit

Hi Sakaz,

One suggestion :
1) Do you have an oscilloscope and can you check if you ARE getting the DTMF tones on those pins ? I had an pre-assembled modem with a RJ jack for a handset.I used the handset jack to take the DTMF tone. Hence I did not have to go deeper into the modem.A problem I still have is that sometimes the DTMF tones are not received.I think its because of some ground loop issue which is corrupting the tone. I have a separate power supply for the modem and my uC board.I am planning to use an audio transformer to isolate the modem output and the uC board with the 8870 and check.However its on the back burner right now.
Since you say it is working with your mobile phone,it probably means your DTMF decoder is working fine.Can you check the waveforms with the mobile phone and with the SIM module and compare both.

Regards

 

[Franck1991]

Re: mt8870

Hello sakaz, please tell me how you connected your phone to the MT8870 ic. please! I need your help.please!

---------- Post added at 14:17 ---------- Previous post was at 14:16 ----------

my email is: franckbery@yahoo.com .