Pic18F4550 + SIMCOM SIM900D GSM/GPRS

[pedja089]

Maybe problem is in supply voltage. Modem works on 2.8V(it have internal regulator), so pic should work on 3.3V, and you must have serial resistor on pic TX. So modem can't draw any current from pic TX pin.

[tacbanon]

Maybe problem is in supply voltage. Modem works on 2.8V(it have internal regulator), so pic should work on 3.3V, and you must have serial resistor on pic TX. So modem can't draw any current from pic TX pin.

Probably that is the case I'm having trouble with...serial resistor? Like a voltage divider?
Here is the general Specification of the GSM
Power Input:
5V-7.5VDC @ 1.5A

I/O Interface:
UART 3.3V Logic 5V Tolerant

Regards,
tacbanon

[mackrackit]

I still think you may need to use a max232 between the PIC and the device as you have mentioned the device works when connected directly to a PC.