I connected my RPI4 & RPI3B one by one with my SIM800L board in hope to be able to receive sms on the board. Unfortunately, the boards do not detect the module. The SIM800l was given external power so that it does not overwhelm the RPI. I connected the GND to the RPI GND, the TX to TX0 and RX to TX0. I have also tried to use ttyS0/ttyAMA0/serial0 to no avail. I tried 2 different GSM boards which both work if interfaced with arduino board but not rpi. I also tried to look using Gammu --identify. But this returns error opening, devices does not exist. I am new to Raspberry pi and i am unable to receive SMS. Please help me out.
Sorry for the bad english.