Hi my USB to UART bridge (CP2102) seems to be broken on one of my NodeMCU Dev Boards with ESP8266.

It seems to be just that specific board since all other boards that I have can be flashed without problems. I have a FTDI Programmer like this one: FTDI Programmer

Now I would like to flash the Nodemcu using the FTDI programmer but I'm not sure how to wire it up. I know that those programmers cant power up the ESP8266 by itself thats why I would use a micro USB cable that doesnt have a data wire to power up the nodemcu.

This is how I would wire everything up: enter image description here

Is this the correct way to wire up the programmer with the nodemcu? I want to be sure that nothing is going to mess up with the nodemcu or the programmer.

NodeMCU FTDI GND ----> GND RX ----> TX TX ----> RX

  • 1
    Looks fine to me. Just hold the FLASH button and tap RST before you want to program to put it into bootloader mode. You may want to try that with the existing USB connection first before you go through the rigmarole of wiring up an FT232 board.
    – Majenko
    Commented Feb 22, 2021 at 16:51
  • @Majenko yeah I tried the build in Serial Connection but on this specific Nodemcu I keep getting: ERROR Running command failed: could not open port 'COM3': PermissionError(13, 'Zugriff verweigert', None, 5)
    – shyney
    Commented Feb 22, 2021 at 16:58

1 Answer 1


Assuming your FTDI Basic is the 3.3V version, then yeah that will work fine provided you that manually reset the board yourself and enter the boot-loader using the buttons.

If you're independently powering the boards you may want to insert some series resistance in the RX and TX connections in case your signal receiving end is not powered while the sending side is. In short you don't want the TX signal from one of your devices (boards) trying to power the receiving device (board) through its protection/clamp diodes.

In regard to comment about resistor value: The value of the resistor depends on what you can get away with in terms of its effect on the signal and how much current is allowed through the clamp diodes on the other board. A couple of Kbyte is probably sufficient, better than nothing in any case. Use a bit more if you can and still get a reliable signal through. If you have the boards both powered before you connect them and you're careful about connecting them, then there's no opportunity for that. It may also just be that they're robust enough that you don't need them at all. I usually put some in though. The second reason which I didn't state above is just that it protects you from being outright stupid and accidentally connecting them to the wrong thing; wrong signal, or to VCC or GND on the other side.

  • which resistors should I use and how exaclty do I wire them up? (The programmer that I have has jumper connectors for 5v and 3.3v)
    – shyney
    Commented Feb 22, 2021 at 17:02
  • They're just in series with the signal, which hopefully will be clear in the above. I'm addressing that only briefly though, otherwise there's more in there about that then just answering the question.
    – timemage
    Commented Feb 22, 2021 at 17:14
  • Is it also possible to connect it like this: imgur.com/a/Tb7Llow I'm not sure if the programmer is going to be able to power the nodemcu up but at least then I dont need to mess up with resistors etc. is this possible?
    – shyney
    Commented Feb 22, 2021 at 19:48
  • Right, that removes the "independently powering" concern. Just be careful your code doesn't do something like use pinMode with OUTPUT on the RX pin and you should be fine.
    – timemage
    Commented Feb 22, 2021 at 19:53
  • Even on an Arduino UNO, where the serial transceiver and and the microcontroller are powered together, resisters are still in place to protect against accidentally driving serial pins the wrong way; it lets people be a bit more careless. What you've shown is something I would do, because I know not to try to drive one of the serial pins opposite the FTDI. If it was something I was putting "into the field" as it were, I'd be more inclined to have them in there, just in case I screw up.
    – timemage
    Commented Feb 22, 2021 at 19:55

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