I'm not at all sure I follow that circuit. But if I do...
- It's overill. The simple four wire DP/two switch method works.
- 3.3v is shorted to GPIO27 throguh aprox 900 ohm
- Won't Q1's base also be pulled low though R2. So no voltage/current will pass between it's collector and emitter. Doesn't that mean that the transiston will in fact do nothing at all? (path of least resistance etc.)
- Is S1 latching or momentary? That isn't clear and is important.
- What's the purpose of GPIO27? If it really is just being used as a ground it doesn't appear to serve any purpose other than keeping the LED on.
- The use of the RUN pin is problematic. Unless you never drive GPIO27 high and allow voltage/current through Q1.
- The RUN pin is active low and does it's thing (hard rest of SoC) on a low to high transition.
- If S1 is momentary you won't get a safe shutdown unless you hold it in until the shutdown has completed. Release it too son and you get a hard reset regardless of the state of the OS.
It also means that should power be removed and reapplied the Pi will do what it always does and boot.
If it's latching, yeah it'll trigger the gpio_shutdown overlay. And it will have no impact on the OS. When released it'll hard reset the SoC. If power is removed and reconnected in the meantime having the RUN pin low will prevent reboot.
Statistics: Posted by thagrol — Mon Sep 09, 2024 10:06 pm
