- D0/GPIO16
- D3/GPIO0
- D8/GPIO15
The selected pin needs to wire to OFF on a Polulu latching circuit 2808 https://www.pololu.com/product/2808 and should only send a HIGH pulse when it's ready to power off. The rest of the time it should be 0V.
I did a bunch of research yesterday comparing the pins ( https://github.com/cheapjack/MileCastles/issues/104 ) and drew the conclusion that GPIO15 would be a good choice, as it's already pulled down (by e.g. the NodeMCU v0.9 schematic I could find), to ensure the ESP8266 powers up in the correct mode.
I was therefore expecting that GPIO15 would stay pulled low and after boot I would configure GPIO15 as an output with an explicit value(0). At a later time I would send it a value(1) and the latching circuit would power everything down.
Imagine my surprise when I did a quick test of GPIO15/D8 this morning with an LED in it. After power up, the LED is bright as day, suggesting that GPIO15 is actively driven high for some reason I can't fathom.
Is there a way to prevent GPIO15 from being actively driven high before I get a chance to make it an output and send an active low?
Alternatively can I make use of any of the other pins to wire a software-controlled pin to OFF, which stays low until configured as an active high? I believed none of the other pins would be reliable, because they are frequently pushed HIGH as part of a power-up sequence.