ESP8266 Community Forum

I have an LED connected to GPIO2 through a 220ohm resistor. When I upload my sketch, the sketch works fine once the upload is completed.

If I remove power, remove the GPIO0 - GND short, and reapply power, the blue LED on the ESP8266 stays on constantly and my LED comes on (should be initially off).

If I remove the connection to my LED, cycle power, and then reconnect my LED, the sketch works perfectly.

Can anyone explain what is happening here.

Thanks,
Marty

GPIO2 is one of the pins used to select boot mode & must be high on startup. Your LED is pulling the pin low. Easy fix: flip your LED around and invert the logic levels in your code.

Thanks Lethe,

You are correct, switching the polarity of the LED fixed the problem.

Is it commonly known about this behavior of GPIO2? I had not come across this in the documentation before.

Now I see a small note on the ESP8266 Arduino Githup site "GPIO2 is alternative TX for the boot loader mode". I would not have read into that statement about preventing the voltage on that pin from going low during boot-up.

Is this situation covered in some other documentation ? It's rather important.

Regads,
Marty

The Boot Process table in Wiki : https://github.com/esp8266/esp8266-wiki ... ot-Process
Any LEDs connected to GND will act as pull-down.