Intro: Creating a Start Relay for a Car Windows Pc.
I'm currently building a car automation pc. This Machine will have an ssd and have my own custom version of Windows 8.1 (slim and very low resources user with the fancy capabilities of touchscreen support).
I'm designing it to be extremely robust and to power on and have windows running without checking any disks for errors. Why? This machine runs only when the engine is running and I am not giving it the privilege of shutting down. Power will simply be lost to it.
Now to start any Windows machine you typically need to press the power button. Tablets and netbook don't have a bios setting to power on with charger connected. I needed a means to simulate pressing the power button for 2 seconds yet delay that 2 second pulse after the engine successfully started.
I decided to use 2 relays for this project. One to delay turning on for 10 seconds which when powered will turn on a digital relay to give the pc the 2 second turn on pulse.
Step 1: Wiring the Two Relays.
Both relays have the same 12 volt supply.
The digital relay I soldered the 12 volt supply and in trigger pins together.
The analog on delay relay I used the normally open contact to switch the 0 volt supply to the digital relay.
Step 2: Testing and Completion.
Now when 12 volt is initially applied, that is during engine crank, the pc will only get a 2 second on pulse after a 10 second delay.
I marked the two contacts on the pulse relay so I can easily connect the power button wire. In fact only one wire I have used at the power button. When this goes to 0 volt, the pc boots up!