I'm using the SIM800L module but i've problems. I'm triying to connect it to the Elegoo UNO i've, but it restarts at all times. Also the led of signal strengh blink every second, so i dont get signal.

enter image description here

I also upload a video to Youtube to explain the problem, this is the link.

Thanks in advance!

  • do not connect Reset RST
    – Juraj
    Commented Mar 8, 2018 at 17:31
  • reset pin of a device should be connected to a gpio pin, to be able to reset the device from sketch
    – Juraj
    Commented Mar 8, 2018 at 17:50
  • @Juraj Doesnt work, now the module seems to restart, the indicator led start blinking and after that get paused for a few secons and start again, idk what to do :(
    – imTDB
    Commented Mar 8, 2018 at 21:57
  • you did not connect it or you connected it to some io pin? the library you use, should have a parameter with the reset pin number and taking care of setting that pin
    – Juraj
    Commented Mar 9, 2018 at 8:16
  • @Juraj i didnt connected, you said that i need to connect it to a io pin and define it on the code?
    – imTDB
    Commented Mar 9, 2018 at 13:38

2 Answers 2


When the reset pin of Uno is connected to ground, the Uno resets. That is what the reset button does.

You connected the reset pin of Uno to other device's reset pin. If the reset pin of the other device grounds the reset pin of Uno (grounds or has lower then required voltage), then Uno resets.

The reset pin of a peripheral device is intended to reinitialize the device by program running in microcontroler by setting a connected GPIO pin to required state.

If you have a library for the device, that library will take care of the GPIO pin controlling the reset of the device.

If you plan to use the device without library, then you should take care of the reset pin in your sketch. Setting the selected pin to OUTPUT and initializing it to required state.

The usual required state for reset is LOW so the output must be HIGH for the device to work.

Some tutorials and libraries require connecting the reset pin of gsm800l to a selected Uno GPIO pin with a transistor, and then reset is HIGH and LOW is for normal operation.


Besides the RST pin situation that the others pointed out, you're not going to do much with the way you're powering the module. It might turn on, but you will never be able to register on the network. You have to power the module with an external power source and common the ground.

Also, if the module you're using is the one on the image, you might need a logic level shifter to use the Tx-Rx connection.

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