Lopy + PyTrack + Gravity UART GSM/GPRS module

[ArnaudM.]

Hi everyone,

I am just starting my PyCom journey and I am yet facing some little problems.

I want to connect an A6 GSM/GPRS module (https://www.dfrobot.com/wiki/index.php/Gravity:_UART_A6_GSM_%26_GPRS_Module_SKU:_TEL0113) to my LoPy board via UART.
The LoPy board is mounted on a Pytrack expansion board and here is my connection :

The Lopy is powered by an USB port of my laptop's dock plugged in PyTrack USB.

My code is :

from machine import UART
import binascii
import utime

def update_serial1():
    print("Waiting for response ...")
    utime.sleep(2)
    while serial1.any():
        print("Data read : <{}>".format(binascii.hexlify(serial1.readall())))

def send_and_wait(what):
    print("Sending <{}> ...".format(what))
    nb_sent = serial1.write(what + "\r\n")
    print("Sent : {}".format(nb_sent))
    update_serial1()

def loop():
    send_and_wait("AT")
    send_and_wait("ATOI")
    send_and_wait("AT+CSQ")

serial1 = UART(1)
serial1.init(baudrate=9600, bits=8, parity=None, stop=1, timeout_chars=2, pins=('P10','P11'))

loop()

But when I launch my AT commands I only receive 'ff' bytes as you can see in the command line extract here:

Could anyone tell me what I am doing wrong ? What am I missing ?

Many thanks for your attention ! :-)

Arnaud