PIC & TC35 GSM Modem comms issue....

Discussion in 'Embedded Systems and Microcontrollers' started by andye456, Jan 9, 2015.

  1. andye456

    Thread Starter New Member

    Mar 8, 2013

    I have been messing round with a 16F690 (on the PICkit2 demo board) and a TC35 GSM module - also on a demo board.

    I have written some C code that handles dialling from an old rotary phone dialler. Sending "atd012345354345;\r" to dial a number and "at+chup\r" to hang up.

    I have a USB/COM cable plugged into my PC and am using Realterm or Putty to communicate over RS232.

    The PIC is outputting to an RS232 level shifter and when I plug the PC's RS232 COM cable into it I can see the commands output from the PIC, e.g. atd012345354345;\r

    If I plug the RS232 COM cable into the GSM module I can send it "AT" and get back OK, or I can send it the atd string and dial a number, to ring another phone etc. - all good so far.

    The GSM module has an on board MAX232 + D9 RS232, but this didn't seem to work so I am using another MAX232 module to level-shift the uart from the GSM.

    However when I plug the output of the PIC into the GSM module - nothing. I cannot send it comms, in fact the Tx Rx lights on the GSM MAX232 don't blink at all like they do when Realterm is sending an AT command to it.

    Anyone got any ideas? I have tried to bypass the max232's altogether but this also doesn't work - different voltages maybe?

    Many Thanks