I have a SparkFun ESP8266 Thing Dev board, to which I want to perform a
digitalRead() on one of the GPIO ports. I'm using
D15, and I'm configuring it for input like this
It does seem to work as intended, and I am able to pull it down by connecting it to ground via a 4.7kΩ resistor.
But how do I know what the actual "correct" resistor would be? I can't find any specs for the internal pullup resistor online. On a related note, I first tried using
D0, but it didn't seem to have an internal pullup resistor, since even using
INPUT_PULLUP didn't turn it on.
Perhaps there are specs online and I'm just not able to find them, but is there any other way (measuring?) to find out which pins will work with
INPUT_PULLUP and if so, what their internal resistance is?