I got a beginner level problem.

I got two esp2866 nodeMCU, they both work with the usb cable and I can get the blink program to run though it. Running them with external power doesn't seem to work though. I expect the blink program to run when I plug them in but I get no led light signal at all. My power source looks identical to this. I got jumpers set on 5V. I don't have a voltage meter but I've tested against my Arduino Uno and it runs as expected when connected to the same wires.

  1. Shouldn't I get the blink signal or any other led signal if the nodeMCU got power?
  2. Any clue to how I could fail to provide power?

thank you!

edit: picture and jack barrel power input: 5V 3A no power to the nodeMCU

  • Consider editing your question to include decent images of your wiring.
    – timemage
    Nov 20, 2020 at 21:47
  • If you're using the barrel jack into that regulator board, the voltage being provided to the barrel jack may also be important to know.
    – timemage
    Nov 20, 2020 at 21:50
  • @timemage- done Nov 20, 2020 at 22:22
  • It seems like the specification of the NodeMCU VIN as working with 5V is very misleading. I have a board that has the same issue as you, and my 5V supply does turn the NodeMCU on, but I can't get the WiFi to broadcast!
    – Gabriel G.
    Nov 22, 2020 at 18:27
  • Read the answer by @timemage. The voltage going into the board is not 5V but some lower voltage, caused by the voltage drop in the breadboard power supply. Add to that the fact that all NodeMCU's are not created equal, especially when connecting things to their power bus.
    – StarCat
    Nov 22, 2020 at 20:37

2 Answers 2


Linear Regulator Dropouts

The linear voltage regulators found on that board are going to expect more than 5V at the barrel jack, because they require a minimum "drop out" voltage. The AMS1117 that is on that board, so far as I can tell, has a drop out voltage up to 1.3V. So you would want at least 6.3V (perhaps better 7V) at the barrel jack in order to get 5V out of it.

So the NodeMCU board may be seeing 5 - 1.3 or 3.7V at the input to its 3.3V regulator, which also requires its own drop out. The output of that 3.3V regulator may then be significantly below what the esp8266 specified operating voltage range.


So I did the tests mentioned in the comments, just to illustrate the problem. And the results are about as expected.

I altered the stock blink sketch that comes with IDE version 1.8.13 to use LED_BUILTIN (as opposed to 9) in the pinMode and digitalWrite calls.

I changed the LOW period, which is LED ON for my board, to 10000ms so that my voltmeter would have time to settle on a voltage test across the LED.

And I uploaded to the board, a NodeMCU 1.0 clone by Hitletgo.

When powered on its USB micro b jack, 3.3V labeled pin of the broad measuring 3.30 V. The LED color is blue, it is bright and it is dropping 2.66V.

Then I switched to powering the NodeMCU board by via of VIN pins from the YwRobot regulator board. I provided 5.05V to the barrel jack. To not great surprise, it does not blink.

The voltage out of regulator board was 3.26V. To be clear, I have this jumper for 5V. As a sanity check, I jumpered it for 3.3V and got about 2.5V out of it. Again, this is unsurprising because it also needs a dropout voltage.

I then measured the "3.3V" header line on the NodeMCU itself to be 2.14 V. Without sufficient voltage into the 3.3V regulator, it is not providing 3.3V out. And what it is producing is below that LED forward voltage when lit. So it is not surprising that it is not lit.

The ESP8266 technical specifications suggest that it can run down to 1.8V. So just for the hell of it I connected the board back to USB and updated the blink sketch to "blink" D8 (or GPIO15) 4 seconds on, 4 seconds off. I did not attach anything to this pin except the voltmeter.

I then reconnected the board to the test rig and found with a meter that it is "blinking" D8 just fine with a logic level consistent with the voltage the ESP8266 is actually receiving.

So in summary, the arrangement here is running the ESP8266 but there is not enough available voltage for it to light the LED. And it is very likely the exact same thing is happening for you.

  • Thank you, that sounds reasonable. I assume then my Arduino Uno was just flexible enough so it could run on 3.7V. Nov 20, 2020 at 22:40
  • @bhenriksson, Possibly. The ESP8266 module may also go lower than the NodeMCU board as whole can. To take a simple example, if your LED is blue, it's possible your esp8266 is still functioning but unable to get enough forward voltage to turn on the LED. You're going to want a meter sooner or later. Sooner probably is best.
    – timemage
    Nov 20, 2020 at 22:46
  • @bhenriksson, tell you what: I will try to locate my NodeMCU clone here and the regulator board that I have of that design. If I'm able to do that, I may update the question with my measurements, as an example. Though it's difficult to say for certain how well this will translate to your exact conditions. In the meantime maybe try to locate a 7V to 9V adapter and try that.
    – timemage
    Nov 20, 2020 at 22:58
  • @bhenriksson, I probably should have mentioned that there's a diode on the on the breadboard voltage regulator board between the barrel jack and the 5V regular that drops additional voltage, very roughly half a volt, which probably explains why the 5V line is lower than the expected minimum of 3.7V. I did not measure it, though. I may update it to include that later.
    – timemage
    Nov 21, 2020 at 0:13

Think of Vin like a car, not enough gas and you will not get there. Over fill it and you could burn it up.

  • 1
    I can confirm the 'burn up' theory. Nov 25, 2020 at 16:53

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