ESP8266 Community Forum

This shows a comparison between two ESP-01 variants.

http://2xod.com/articles/ESP8266%20ESP- ... ison-1.jpg

I've got several of the dark ones. But one of them is missing that resistor next to the pin header.

I wonder what that does. Should I be worried? Seems to work fine, though.

Hi, I also have some blue and the black like you. I did check this out, I'm sure it was a pull up resistor on REST. The early ones suffered from a resetting problem and I'm sure this was put on some boards to prevent this happening if REST was left floating.