Starting my PC with a 3.3v arduino pro mini?



  • Hi,

    I'd like to start my PC using an Arduino Pro Mini (3.3v) but I am not sure how to hook it up.

    There are a lot of tutorials (if you include esp8266 devices) but I am not sure which parts I exactly need. In essence I need to pull the power pin high that is connected to the power button (if I understood correctly).

    7464c810-3489-48e6-ac30-4d043fbe3aa6-image.png

    So on my mainboard (Gigabyte Aorus B450M) that means I connect RES+ to a pin on my arduino and RES- to GND, right?

    There is a 3.3v pin on the mainboard (schematic), can I connect the arduino to that pin to power it?

    And the most important question: Do I need any other parts? Is the voltage higher on RES+? Does that mean it can fry my arduino?

    And in case the question comes up: I can't use wol because I disconnect the PC from power when off. That is apparently against the wol specs and only works in a few cases (of which my mainboard apparently isn't one).

    Thanks for any help!





  • Thank you. It seems I have some groundwork to do and learn how to read the schematics 😄 That hasn't been necessary until now. I'll do that and come back here when I understand enough



  • So I think I understand the main part of your drawing: The optocoupler keeps the Arduino circuit separate from the mainboard circuit to prevent a short. The resistor is for the diode inside the optocoupler.

    There are a few things about your drawing that I don't understand:

    1. Why is there a 5V powerline with a diode?
    2. What does the MB stand for? Mainboard
    3. Why are there two connection points from the Mainboard? Is one reset?

    I tried my first Fritzing to make sense of this and to show how I would design the connections (doesn't mean it's right).

    fritzing1.png

    PW+ and PW- are the pins from the schematic in the first post. , 3,3V and GND are available on another set of pins on the mainboard. Would this work?



  • @kiesel Great work! 🙂

    1. 5V connected through diode to protect of polarity revers
    2. MB = Motherboard, you right
    3. First need to connect power button from front panel, second to connect to "Power Switch" on motherboard. This allows power on both from power button and Arduino.

    You disign is absolutely working!



  • @cabat

    Cool, thank you for your help!

    Should I use a diode between 3.3v and GND too? And do I need a resistor in the mainboard-side of the schematic? Some people used them to protect the optocoupler from high current but I guess there isn't a high current when the power button is pressed?



  • @kiesel I don't undestand - why you want to use diode between 3.3V and GND?
    About resistor on the mainboard side - i don't use it and all works fine 🙂



  • @cabat

    To protect from polarity reversing, like you did in your sketch. Sorry if that's a stupid question!





  • @cabat

    Ah, ok, I get it now. The diode protects me from wiring this up with POWER and GND switched. So I would use it like this

    2f1f33db-fcc8-4a8e-8519-f2de7ef351d3-image.png

    But I guess I can't because of the voltage drop. I think that's out of specs for the PC817. And anyway there is a very low chance that I will wiring this side of the schematic up wrong.

    I guess I was just confused by the lower part of your drawing.

    Thank you VERY much for your patience! I'll supply pictures when I have this hooked up in the hopes they will help others.

    Have a nice weekend!



  • @kiesel Sorry friend, I guess I confused you a little ..
    The diode is needed so that, when powered from the contacts on the motherboard with 5V, it does not damage my arduino, that's all 🙂
    Have a nice weekend to!



  • @cabat

    If I wanted this protection where would I put it in my schematic? 🙂

    Between ground an 3.3v?

    /edit: no between the arduino and 3.3v from the Mainboard, right?



  • @kiesel Yes, you rigth - between 3.3V on mainboard and VCC of arduino!


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