[SOLVED] Problem with PIC and SIM900 communication

[ernpao]

Hi, we are currently working on a project which involves interfacing a PIC mcu to a SIM900 GSM module. So far, we have been able to test the GSM module through hyperterminal and we've been able to send text messages to our phone. We've also programmed a PIC 16f877a to send AT commands through the UART and we've verified that the program and circuit works and that the commands it sends are correct using mikroC's USART tool. But our problem is that when we try connecting the PIC to the GSM module, the gsm module doesn't seem to respond (our PIC was programmed to wait for the GSM module's responses as well). I'm pretty sure that the UART of the PIC can be connected to the USART of the SIM900 module right (SIM900 accepts ttl levels?)? And we've checked our connections too - TX of PIC to RX of SIM900 and TX of SIM900 to RX of PIC. Thanks in advance to anyone who can help us

 

[taroot]

you did not mention that which PIC is 5v or 3.3v. if it is 5v pic then you need to a voltage converter between sim900's TX and Pic's RX. sim900 output voltage level is 2.7-3v. Pic I/O input high voltage are 4V. So use a voltage level converter (3.3 to 5v).

 

[ernpao]

yes that did it thank you very much taroot! I forgot to check the voltage levels of the logic the PIC and GSM module are communicating now and we are able to send text messages, but the messages we receive contain the AT commands as well, how do we remove those? thanks again

 

[taroot]

SIM300 in Echo mode so each command it received at its Rx will be sent back on its TX.There is a command in SIM300 AT manual that will off the echo mode. May be "ATE0"