I have a 16x2 LCD display that is connected to an Arduino microcontroller. It is working fine but the LCD display flickers when I connect the Vin and GND of the main board to its slave GSM Shield.
I used main board Vin and GND to power up the GSM Shield so I only have one power supply. I was able to power up GSM Shield by adding jumper to Vin and GSM +Vin.
In additional question, is there any other way to power up Arduino GSM Shield without connecting it to another power source to still keep having only one plug for power?