SIM908c GSM module with Arduino Mega without any shield

Hello,

I needed to work with GSM so I bought a SIM908c module. Also I bought a breakout board to connect with Arduino Mega. I am using the gsmlib library for this module.

My connections are as follows:

3.5V 1A power input + 100uF bypass capacitor => VBAT

3.5V 1A power input + 4.7uF bypass capacitor => VRTC

Power Adapter ground => GND

Arduino Mega pin 53 => PWRKEY

Arduino serial TX1 pin 18 => TXD

Arduino serial RX1 pin 19 => RXD

Power Adapter ground => DTR

Now I am using the library example of AT command named GSM_GPRSLibrary_AT. After uploading the sketch and observing the serial monitor the following responses show up:

GSM Shield testing.
ATT: OK
RIC: AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

DB:ELSE
ATT: OK
RIC: AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

DB:ELSE
ATT: OK
RIC: AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

DB:ELSE
ATT: OK
RIC: AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

DB:AUTO BAUD RATE
ATT: OK
RIC: AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

DB:NO BR
ATT: OK
RIC: AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

DB:NO BR
ATT: OK
RIC: AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

DB:NO BR
ATT: OK
RIC: AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

DB:NO BR
ATT: OK
RIC: AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

DB:NO BR
ATT: OK
RIC: AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

DB:NO BR
ATT: OK
RIC: AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

DB:NO BR
ATT: OK
RIC: AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

DB:NO BR
Trying to force the baud-rate to 9600

1200
ATT: OK
RIC: AT+IPR=9600
AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

2400
ATT: OK
RIC: AT+IPR=9600
AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

4800
ATT: OK
RIC: AT+IPR=9600
AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

9600
ATT: OK
RIC: AT+IPR=9600
AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

19200
ATT: OK
RIC: AT+IPR=9600
AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

38400
ATT: OK
RIC: AT+IPR=9600
AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

57600
ATT: OK
RIC: AT+IPR=9600
AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

115200
ATT: OK
RIC: AT+IPR=9600
AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

ATT: OK
RIC: AT

ERROR: SIM900 doesn't answer. Check power and serial pins in GSM.cpp

status=IDLE

This kind of responses appears even if I don't give any power to VBAT and VRTC. I am definitely did something wrong but I can't figure it out. Please kindly help.