ESP8266 Community Forum

- Fri Jul 07, 2017 6:53 am #68024 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?

- Fri Jul 07, 2017 7:43 am #68025 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.