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Giving the system the boot « Kevin's Projects

Giving the system the boot

The time has finally come to wire up some voltage and hit the power button.

This is trickier than it sounds, however. I want to be able to do bench tests, outside the car, so I needed a way to provide DC voltage just like a car battery, anywhere I wanted. I also wanted to add a switch that would imitate the ignition switch in the car.

I happened to have an AC converter that provides 120 Watts at 12 Volts through a 5.5mm barrel plug. Since car batteries are designed to provide 13V but can vary anywhere from 9-16V, my 12V adapter should work fine.

The power supply has three pins for power: battery power (+), battery return (-), and ignition. When the ignition pin is shorted to the battery power pin (i.e.,voltage is applied to both pins), the power supply assumes the ignition is on and fires up the power to the computer. Conversely, removing the voltage from the ignition pin shuts down the power supply. So it was a simple matter of wiring the 12V from the AC adapter to the battery power pin, and adding a switch that also sent the same voltage to the ignition pin. Ground from the AC adapter would go to the battery return pin.

Wiring schematic for bench test power

Wiring schematic for bench test power

Here’s the first solder on the switch, which is a plastic toggle I found in a box of parts:

First solder...

First solder…

I got everything wired up and soldered in place:

Final switch connections.

Final switch connections.

And then taped everything up for safety and to prevent inadvertent shorts. There’s at least one layer of electrical tape between all the pins.

All taped up.

All taped up.

Plug the whole thing into the computer and we can see from the three lit LEDs that the power supply is providing the correct voltages! The 12V power wires are coming from off-camera right in the image below. The green light on the left is motherboard standby power, indicating that it has a good 5V signal; the middle green light is power supply power, indicating that it’s on; and the right blue light is the motherboard power, indicating that the motherboard is up and running.

Power applied

Power applied

All that was left was to pop in the USB stick with my Gentoo livecd, and boot the computer!

First boot!

First boot!

Here I’m using my desktop monitor because I haven’t installed drivers for the touchscreen yet. That’ll be part of operating system installation, coming soon.

 

 

Categories: Carputer

Comments

  1. Up and running! Woohoo! Can’t wait for the next post…

    Jennifer / July 29, 2011 / 10:07 am