Its interesting to note that the O.P of the thread you just linked to ended up going with a MCU based solution in spite of several possible discrete or logic gate based solutions being offered.
I happen to know him very intimately since long time, we usually (but not always) agree.
I'm trying to have the laptop turn on when my car turns on, and it will act as a server
And so we discover that:
- Mains does not enter the picture
- There's an available always on power source that can stand a small load (e.g. an MCU)
Given the above, a small MCU seems a good idea, one could implement a simple state machine that:
- Tuns on the laptop when the car is turned on
- Shuts it down when the car is turned off
- Maybe supports its own button to override the automatism (so the laptop can be tucked away and its button needs not be reachable)
In fact, I have designed something very similar with an ATtiny, for a friend who wanted to change his iMac G5 mobo with a NUC one.
I attach the code below, if it can be of inspiration, it also understands a flashing LED for sleep mode to disable the iMAC backlighting.
The code has been tested on target with a PSoC based rig to simulate all the surrounding HW, but not on the field, as my friend did not go through with his idea...
the voltage difference between the button and the led are both 2.8v
This is not very clear, the real question is whether one side of the button (and of the LED) is connected to ground.
If not, we will need something as a small relay, or an analogue switch (CD4066?).
Edit: Missing license in the code.