Hello everyone, I'm new to the arduino world!
I am currently working on a project, where I need to connect a GSM shield and an accelemeter simultaneously. I 've read that GSM Shield use UART protocol while the accelerometer uses i2c. When i connect them both, the accelerometer stops communicating with arduino. So, I really need your help. Which are the steps that I need to make to be able to read data from the accelerometer and be able to make calls from the shield at the same time?
Thanks in advance!!!! 
You must use nonblocking code to read and write to the devices. How you do that would depend on which libraries you are using.
The shield and the accelerometer I am using is from adafruit, and specifically adafruit FONA 808 for GSM and the adafruit MMA8451 for accelerometer. So, I use the libraries adafruit provides for these 2 products. I think that FONA 808 library uses also the wire.h library. Do you want me to tell you exactly which libraries are included in adafruit provided libraries?
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