I'm having the following situation: When I connect the Arduino Uno Revision 3 to the SIM 800L v2 GSM Module everything works, if I test the code from here:
I'm powering the GSM module with an additional power source.
But if I run the same code (except the values of the pins) on a Mega 2560 v3 board, only the sending of the SMS and initiating voice calls works. Receiving SMS is not working. From what I can see for the Mega board case the data sent from the GSM Module does not reach Arduino. No data is available on the serial connection. Some data should be visible in the Serial Monitor, even when sending SMS. (It is visible on Uno board and not on Mega, even if Mega commands the GSM module to send successfully the SMS to my phone).
I've tried a lot of various pins combination from the board. I have even connected the GSM Module VDD pin to 5V or to the IOREF pin from the Mega board. (For Uno it works without using the VDD pin.) If I measure the voltage between the RX or TX pins and the GND the value is 4,95 V. Same value between the IOREF pin and GND.
Why it is working on UNO board and not on the Mega?
Is SoftwareSerial library failing on Arduino Mega board?
Do I need to perform some jumpers setting on Mega?
Is there an issue with TTL/ voltage levels?