ESP8266 Community Forum

Hi all,

I'm trying to use the TX pin as GPIO output. I'm using the nodemcu firmware.

If I try and power on the module with it connected then it doesn't boot, but if I connect the pin after boot then it works fine.

This only happens with one particular circuit I've connected it to - it also works fine with some others I've tried (using it to drive a relay). It also works fine if I use GPIO2 instead.

The circuit is pretty simple:



Any ideas what's going on? As far as I know the TX pin shouldn't need to be high/low/floating in order to boot, right? It is set as a GPIO output as soon as it has booted, but it doesn't seem to get that far. Any ideas how else I can debug this? I find it hard because obviously I can't do it while connected to a serial port.

I'm probably just going to work around this by swapping it with GPIO2 on my circuit and in code which will sadly make a mess of my layout, but I'd quite like to understand the problem so I know the limitations when designing circuits in future.

Thanks!

So, to answer my own question, it seems to be fine if I add a pull-up resistor.

No idea why that is required, but there you go.

BTW, this wiring looks very bad : there is no current limiting resistances across the 2 leds ...

this gives me an idea, can I use TX and Rx for sale and sea, for use with the OLED i2c screen?