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Interfacing PIC16F877A and SIM300 gsm development board

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Newbie level 6
Nov 11, 2009
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I bought a SIM 300 development board and I connected it with the PC and It works fine. I can send SMS and everything. But when I connect SIM300 developement board with PIC16F877A microcontroler, it does not work. I connected Rx and Tx pins through MAX232 and the GND pins only(Same as when communicating between PC and PIC16F877A). I want to send and receive SMS. Can anyone Help me Please. It's urgent!!

One clarification Sawula. In what way you tried to interface GSM with PIC MCU. Whether you interfaced GSM Eval. Board to PIC MCU or GSM module itself to PIC. If you are interfacing GSM module to PIC no need to use max 232. bcos GSM module is also TTL compatible so you can directly interface the MCU's TX and Rx to GSM Tx and RX. Onemore thing RTS and CTS of the GSM module has to be shorted(This is hardware cheating). you told that you were communicating GSM Eval. board with PC in that CTS and RTS will be taken care by PC itself. (I think u r using hyperterminal rigtht?)

All right I removed the MAX 232 and I connected 25 pin of the PIC16F877A(Tx) to the 3rd pin of the female serial port connector of the modem and 26th pin(Rx) of the MCU to the 2nd pin of of serial the connector. And the 8th pin (RTS) and 7th pin CTS is shorted. And the 5th pin of the serial port is grounded. But I am not getting any response from the modem.

Then I grouded both RTS and the GND pins and disconnect CTS pin. But still it is not working. Do I need to connect any other pins please help me!!!
But previously I check both pc to modem and circuit to pc serial communication were successful.

Hello sawula. I hope you know about TTL and Rs 232 Logic Levels right? If you interface GSM Module (chip set) no need to use max 232. If you interface GSM Eval board (not GSM Module)with PIC you need to use max 232. Please refer the attachment. One more thing check the GSM module whether is it powered up properly or not? Better you provide an external switch circuit for Module On/Off. Later you can switch GSM Module On/Off by PIC itself.


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I got your point thirugnanam.ram. And now it works fine. Thanks dude.

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