Just need a little help... I'm trying to turn on the SIM800l, but the device is not working. I'm using a 5V power with a voltage divider (10K - 47K) to the device requirement of 4V Vcc, but the LED doesn't turn on... I tested the Vcc and GND and there are no short circuit, and (just to check) I tested the LED and it worked. I want to know if the module is destroyed or something and if there is a test that I forgot to check. Thanks!!! enter image description here

  • 1
    measure the supply voltage at the SIM800l pins when turned on ... your question is not about arduino, so it does not belong here
    – jsotola
    Sep 23 at 0:43
  • Thanks! Sorry but I'm using this for a arduino project. The supply voltage gave me 4V (like the vcc) and all the others pins (tx, rx, reset, etc) are high (3.5V average). I'm thinking that it could be broke
    – CIBS16
    Sep 23 at 2:22
  • no, it is not an Arduino question ... the Arduino is irrelevant to the problem ... you can use a voltage divider only if the current through the divider does not change ... you must not issue any commands to the SIM800l, otherwise the current consumption changes and the voltage drop across the divider changes ... you did not measure the voltage correctly
    – jsotola
    Sep 23 at 2:35
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    you can't power devices over voltage divider. it reduces the voltage and current so there is no power
    – Juraj
    Sep 23 at 5:01

1 Answer 1


I'm also working on the SIM800L project. it's better to lower the power to 3.7V - 4.0V using 2 diodes 1N4007 in series, now my project is running normally. main source (5V) of VIN ESP32. or you can check using the LM2596 buck converter to reduce the voltage.

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