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    GSM interfacing with PIC32mx440f256h microcontroller

    Hi, I am trying to interface GSM using SIM800C with a pic32mx440f256h microcontroller. The GSM module interface pins are as follows:

    GSM_Reset Pin -> RD5 (pin no 53)
    GSM Serial Interface on U2RX and U2TX (pin no 31 and 32)
    GSM Power Supply RE7 (pin no 3)

    I am trying to send SMS using the same assembly but unable to do it. Please help

    I am using MPLAB IDE with C32 compiler

    Thanks

    •   Alt12th March 2018, 10:30

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    Re: GSM interfacing with PIC32mx440f256h microcontroller

    If this is a new project then I recommend that you get the latest IDE (MPLABx) and compiler (XC32) as they ones you are using are many years out of date (and support).
    You have told us very little of use without a schematic and the small but complete code that shows how you are trying to interact with the SIM800C.
    For example, what do you mean bu "GSM Power Supply RE7"?
    Also how do you know it is not working? What tests have you done, what results did you expect and what did you get?
    Susan



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    Re: GSM interfacing with PIC32mx440f256h microcontroller

    Hi, GSMP power supply RE7 meaning GSM power is operated by pin RE7 on a pic32mx440f256h controller. I have dumped sample code on controller for SMS sending function but unable to get the SMS on defined number

    Please provide if you have a sample code for this or kindly suggest what register configurations I'll need to configure to get the functionality, I'll work on AT commands part

    Thanks



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    Re: GSM interfacing with PIC32mx440f256h microcontroller

    Hi,

    The lack of a schematic makes it difficult to understand....
    Are you sure a microcontroller I/O pin is able to provide enough current with low voltage drop to supply a GSM modem?
    Usually a port pin is meant for (low current) data communication a d not as power source.

    Klaus
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    •   Alt13th March 2018, 07:07

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    Re: GSM interfacing with PIC32mx440f256h microcontroller

    You didn't yet clarify which part of the communication you have problems with.

    Do you manage to get any response from the modem? E.g. send AT\r, get \r\nOK\r\n?

    If not, check power supply, serial connection, required state of handshake signals, baud rate. If you rely on autobauding, consider that initial "A" "T" "\r" must be send with delay between characters.

    If you get a basic response, your problem is apparently in understanding AT commands.



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    Re: GSM interfacing with PIC32mx440f256h microcontroller

    Quote Originally Posted by FvM View Post
    You didn't yet clarify which part of the communication you have problems with.

    Do you manage to get any response from the modem? E.g. send AT\r, get \r\nOK\r\n?

    If not, check power supply, serial connection, required state of handshake signals, baud rate. If you rely on autobauding, consider that initial "A" "T" "\r" must be send with delay between characters.

    If you get a basic response, your problem is apparently in understanding AT commands.
    I am not able to get any response from SIM800C module.
    Power supply is OK

    If you could share the configuration for baud rate & other register settings it would be helpful

    Thanks



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    Re: GSM interfacing with PIC32mx440f256h microcontroller

    According to the SIM800C data sheet, the current draw depends on what the device is doing but only "Idle" mode has a current draw less than about 100mA.
    The maximum current that can be drawn from an I/O pin on the PIC32MX440F256H is 25mA (data sheet, Absolute Maximum Ratings table, page 151).
    Therefore as soon as you tell the SIM800C to do anything then it wil drawn more current than the PIC32 can supply through its I/O pin and it will (probably) shut down - either because the voltage will drop below the minimum of 3.4V (SIM800C data sheet) or the PIC32 will destroy itself trying to source the current. I see the SIM800C can draw up to 2A (max)!!!!!
    Also the typical operating voltage of the SIM800C is 4V with a minimum of 3.4V. I don't know what voltage you are running the PIC32 at but it has a max of 3.6V. At that voltage, the minimum Voh of an I/O pin is 2.4V at 12mA and any higher current draw may well drop that further.

    Bottom line: powering the SIM800C from a PIC32 I/O pin is doomed to fail! You might have it work while nothing is going on, but it will fail.

    Just don't do this!

    The SIM800C has a PWRKEY pin that will put the device into "Power Down Mode" where it will draw 130uA (typ - 150uA max) and *this* is how you should have the PIC32 control the SIM800C.

    As to why the device is how working for you, you really do need to provide is with the schematics and your code (small but complete sample code that exhibits the problem; include the config settings).

    Susan



    •   Alt14th March 2018, 00:54

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    Re: GSM interfacing with PIC32mx440f256h microcontroller

    Hi,

    It's a ridddle without schematic ... to see how the module is powered.

    My opinion: I think riddles are a waste of time when discussing technical problems.

    Klaus
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    Re: GSM interfacing with PIC32mx440f256h microcontroller

    post schematic first?

    pmk



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