Pic18F4550 + SIMCOM SIM900D GSM/GPRS

[pedja089]

Usb-TTL serial module use true 3.3V uart.
You port setup was ok, because you menage to get signal from modem, to pic, and send it to pc from pic...
Also TX from pic is ok, because you get result(post 17) on PC when you connect USB module to modem tx...
So check your ground, and check pic input type, maybe 2.8V isn't enough to ensure logic 1.

[tacbanon]

@pedja089
I checked the grounding..but still no changes.
Sorry for being a noob, but I tried to get the voltage from GSM Tx(4.2v) Rx(4.9v). I also tried to use max232..and still no positive results...I'm totally lost

/tacbanon

[pedja089]

I'm have board with sim900 connected to pic. Modem have 4V supply, pic have 3.3V.
SIM900 use TTL 2.8V true uart, not inverted. I put just 2 resistor in series with comm lines.
If you connect modem to rs232 side of max232, probably you frayed modem port.
1. Connect modem and usb board, and check that.
2. I tell you to try to connect your usb board to PIC instead of modem board. So you can check that communication is ok on PIC side...
You didn't try that...
So try to send response from PC to PIC. Only in HSERIN put longer timeout, eg 5s..
3.You said in post 10 you menage to get signal level. So your hardware setup was ok.

[tacbanon]

@pedja089
Hi sorry took me so long to reply...in post #10 I was able to get the signal level only once(upon power on)...I have to reset my LabX2 to get the reading again. I will try to get another GSM module probably by next week to see if the result is the same...and post here the output. Thanks all for the help and more power to PBP forum!

Regards,
tacbanon

[pedja089]

If you get once reply from modem, your hardware was ok.
Is anything was wrong you won't get reply if you restart or not...