GSM/GPRS/Bluetooth HAT for Raspberry Pi 3B+/3B/2B/Zero/Zero W Based on SIM800C, Allow Pi to Send Messages, Connect to Wireless Internet, Transfer Data via Bluetooth, UART Interface

Hi, Many hours of soul searching but was worth it, now fully working with our range of GSM's and a lot faster due to 3g and 4g, we were using just 2g but looking to future proof, tried contacting their support, wouldn't bother if I was you, hardest part was changing baud rates to match, don't bother using cp2102 through usart I have had issues before with the M2M software, I use Ft232rl much better, why ? who knows I'm an end user not the designer ! I have given it a 3 Stars not for the product but the support, the product gets 5 but the support gets 1 hence the 3 !! I'm not using PI or Raspberry so don't ask for help with those I design my own boards and hand shake between sim modules and PIC devices.

It took me a long time to get this working reliably with my Raspberry Pi.When plugged directly onto the Pi it worked but was unreliable which I beleive was due to current limitations. I then unplugged from the and wired it up next to the Pi (this actually suited me as I wanted to git another HAT anyway).The Rx/Tx lines were only 75mm long but the communication was extremely unreliable. One day it would work but another day and I couldn't get a response from the AT command. After I twisted the Rx/Tx wires and the communication became 100% reliable.So, in summary, for best reliability, I found that it worked better if not plugged into the Pi, decent 5V supply direct to the board and twisted Rx/Tx wires.

Needs a fair bit of tinkering to get it to workMost importantFeeding the power to the board not through the pi increased reliability with network connectivity