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By pavanvd
Hello All,

I am interfacing a SIM800 GSM module with Pi 3 over serial ports (pins 6, 8, 10). While things work OK most of the time, every now and then I get spurious characters in the response. For example, I get:

['+CLCC: 1,0,2,0,0,"+919812x\x9c\xd3\x13\x93\x93\x12)\xa25,""', 'OK']

whereas the expected response is: ['+CLCC: 1,0,2,0,0,"+919812012321,""', 'OK']

As I said, this happens once in a while (may be 1 in 10) and happens with other commands too. Also, this is not the only GSM module or Pi having the problem. So very unlikely hardware issue, unless the GSM module is buggy. The GSM module in question is this

The baudrate is set to 9600.

What could be going wrong? Could it be bad connections? I usually crimp dupont connectors to the open ends of the cable supplied with the modem. As far as I can tell, the crimps are decently done. How do I fix this?

By pavanvd
paulvha wrote: Thu Sep 20, 2018 8:28 am the "real" serial port on Pi3 is set by default to communicate to the on-board bluetooth. Make sure to disable. There are many articles around that e.g. see ... ding-pi-3/

Hi Paul,

Thanks for the response. I am very sure that I have setup UART correctly. Bluetooth is disabled.
Code: Select all
$ ls -lrt /dev/serial*
lrwxrwxrwx 1 root root 5 Sep 21 12:17 /dev/serial1 -> ttyS0
lrwxrwxrwx 1 root root 7 Sep 21 12:17 /dev/serial0 -> ttyAMA0
Things work mostly. But the problem is with that erratic response once in every 20 times may be, especially to CLCC commands.