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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?

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  • What Arduino model? What's the supply you attached to Vin, what's it's nominal voltage, and what voltage do you measure when it's attached? What model GSM board? Why hook GSM to Vin instead of +5?
    – James Waldby - jwpat7
    Commented Nov 14, 2015 at 5:07
  • GSM is notorious for very high pulse power demand when transmitting, which can easily cause a supply brownout. Capacitor solutions are possible, but some have resorted to using a battery to power the radio.
    – Chris Stratton
    Commented Nov 14, 2015 at 6:18

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This sounds like either your GSM Shield is drawing to much power (from time to time) and thus your Vin drops resulting in flickering or your GSM Shield induces ripple on top of your Vin.

To debug this I would recommed to have a look at Vin with an oscilloscope and see how stable Vin is. Additionally some capacitors between Vin and GND (100nF and 10-100µF) and a ferrit between Vin and the GSM Shields Vin might help.

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