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SilverFire / esp8266-pc-power-control

ESP8266 based PC power controller
MIT License
48 stars 12 forks source link

Why Pullown-Resistors on PWR&RST lines? #2

Open WillemJansen opened 5 years ago

WillemJansen commented 5 years ago

Hi, quick question: Why did you use pulldown-resistors on the signal lines? To my understanding, pull-up/down-Resistoirs make sure your device has a steady state ... which in this case should rather keep the RST & PWR-line at 3.3V to leave the PC functioning?

Regarding the LED line, I think this makes sense to battle stray capacities.

SilverFire commented 5 years ago

Hello. Thank you for your question and sorry for a very late answer. I am not an electronics engineer, so this schematic probably has a lot of strange things :)

You are absolutely right, RST and PWR lines must be kept with +3.3V to keep PC working. Say we want to "press" the PWR or RST button, so we should pull down the signal lines.

When ESP8266 pin is set to Output mode with LOW (see this code), the microcontroller bypass current does NOT provide sufficient voltage drop to make motherboard think that button is pressed. But with 20k resistors it does :)

I would say that it was a dirty hack to get working board as easy as I can. I think it will be better to do the same using transistors, but the board already works for 2 years with no problems, so I will not touch it :)