ESP8266 Community Forum

Using the ESP8266-07 I have followed a guide to trigger a relay through a web page.
When I first tried this I defined pin 4 for the trigger. With only my multimeter on pin 4 it wouldn't go high or low, but simply defining the output pin to pin 2 worked. I was able to read high and low readings through my multi meter, but when I then used this pin to trigger a FET to run the relay it wouldn't allow the ESP to start properly. This pin would start high, then go low and I believe the circuit was loading this pin down.
Anyway, when I re defined the pin yet again to GPIO16, it works great. This pin stays low during start up.

I know there are a lot of variables to how things are hooked up, but is there a really good write up on the esp pins and how they work?

This page goes into the details of the IO pins at different times. Unfortunately it is not very easy to understand although it does go into details.

https://www.mjt.me.uk/posts/esp8266-gpi ... and-reset/

GPIO 4 and 5 are in an input configuration at startup. GPIO 15 must be low in order to start executing your code (along with 0 and 2 being high). I have used 15 when I needed a low at reset. (driving a relay driver circuit).

GPIO 12, 13, 14 seem to have an internal pull up resistance enabled at startup.