Building a kill-switch for the Acura ITX

Published by Andrew Hreschak in the hardware, cables & wiring, power
Published on 05/01/06 @ 07:56:00 pm using 535 words, and has 6852 views

The Acura ITX car computer project is being designed so that the mini-itx computer system will operate in as hands-free a manner as possible. Since the mini-itx system will be mounted in the trunk, we don't want to have to open the trunk and press the power button on the carPC each time we intend to drive anywhere.

By using the OPUS 120 mobile PSU, we can essentially hardwire the mobile computer into the ignition system of the Acura CL. Hence, there is no longer any need for an ON/OFF button on the computer system. Simply turning the key to start the car will cause the computer system to boot up as a normal computer would. Likewise, turning the car off will trigger the computer system to shutdown gracefully (or go into standby, suspend, or hibernate modes).

Since both the car computer and the MTSVO-SC retractable LCD touchscreen will be wired directly into the 12V ON battery tap under the dashboard, the computer will always start when the key is turned to start the car. But what about those times when we just want to pull the car out of the garage to wash it, change the oil, or drive two miles to the grocery store? There's little sense in having the computer boot up when it will just be shut down five minutes later, right? So why not place a "killswitch" inline on the ACC wires which lead from the ignition to the mini-itx system and the MTSVO-SC touchscreen?

Unused dashboard switch slug

I removed one of the unused "slug" spacers from the Acura CL dashboard (similar to the one below), and took a quick trip to a local auto parts store, where I found a simple SPST (Single Pole, Single Throw) switch with a 30Amp max load. True, 30Amps is pretty much overkill for this particular situation, since the ACC leads on the OPUS 120 and the MTSVO-SC LCD draw only approximately 5mA each, but 30Amps were the lowest switches I could find and it didn't make sense to drive all over town trying to hunt down a smaller switch with the oil companies jacking the price of gas the way they are... So... we'll use a 30Amp SPST switch with a pretty blue LED light built into it.

SPST switch mounted in unused switch slug

Taking the empty slug and a hole cutter, we cut a hole as carefully as possible for a manual cutting job, and slid the switch through. The fit is pretty tight, though the switch can be rotated with enough force, so a drop or two of epoxy or cyano-acrylate might do well to hold the switch securely in place.

Underside of SPST switch mounted in unused switch slug

The underside of the SPST switch reveals the Power, Load, and Ground plugs onto which the series of spade connectors will be attached to provide power from the ignition and to pass it on to the ACCessory sensing circuitry of the OPUS 120 and the MTSVO-SC touchscreen. I think it turned out pretty well.

Continue on to Part 2 of this story:
Building a Kill Switch for the Acura ITX, Part 2

Contemporaneous Auditory Narcotics:
or, What my speakers are currently pumping...
Jimmy Cliff - Greatest Hits

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