Setting Up an In-Car PC, Part 4

So far in this series we’ve covered an overview of installing a PC in a car (Part 1) , getting audio into the car’s original sound system (Part 2) , and installing a suitable LCD screen (Part 3)

As those of you who have read each part will know, along the way we found it necessary to build a noise filter for the audio and a new power supply for the LCD – but both bits of electronics were simple and cheap to put together.

In this story we’re going to finish the installation, allowing you to have a fully-functioning PC in your car to play MP3s through your car sound system, do digital camera downloads – you name it.

Mounting the PC

In this budget system we’ve stuck with an absolute garden-variety secondhand PC. In fact, the Pentium 2 powered PC that we’re using was discarded from a child care centre, ie picked up for nothing. Taking this budget approach means that we’re using a normal hard-drive, rather than a laptop design. Conventional wisdom is that a PC hard-drive won’t last very long (like, 5 minutes) in a car because of the g-loadings it’s subjected to. But we’ve overcome that with a very effective suspension system for the PC.

• Vibration Reduction Design

Start looking at vibration reduction technologies and you’ll soon realise that it’s not nearly as simple as whacking a few pieces of sponge rubber under the PC case.

One of the best basic guides to vibration isolation can be found at Fabreeka.com. A point made in that paper is the natural frequency of the material used to isolate the device (rubber, springs, etc) must be well below the frequency of the vibration that you’re trying to prevent getting to your device. So, if there’s a 15Hz vibration, the material that you select to isolate against this vibration must have a natural frequency well below 15Hz. If it isn’t, there’s a very real possibility that in fact the vibration will be amplified!

Unfortunately, in a car you have a helluva lot of vibrations occurring at all sorts of frequencies. The lowest is likely to be the natural frequency of the car’s suspension itself, while higher frequency vibrations might come from the engine or exhaust resonances.

The isolation medium likely to provide the best vibration protection is a pneumatic design – in other words, air suspension. Air suspension has the major benefit of having a very low natural frequency while still having a good load-bearing capability. The rate (degree of resistance per unit of compression) also rises as the air gets squeezed into a smaller volume, which means there’s less likely to be bottoming-out.

Hmm, all sound pretty expensive? It doesn’t have to be!

• Doing It

The cheapest and easiest source of air suspension that we could find was rubber balls. After looking at all the balls in a large sporting goods store, we settled on rubber practice tennis balls – they appear to be about two-thirds the size of normal tennis balls and are a bit softer. Importantly, the carcasses of the balls don’t offer much stiffness – it’s the air within that provides the springiness.

Placing four of these balls – one under each corner – of the flat-case style of PC that we are using gave excellent vibration isolation over a wide range of frequencies. Importantly, it also provides the travel to cope with big bumps – something rare in normal vibration control. (If using a vertical case, you’d use eight of the balls, one at each lower corner and one at each upper corner.)

Ideally, we were looking for balls with an internal damping medium in addition to the air. (Like super-large squash balls?) The downside of using the practice tennis balls that don’t have internal damping is that the PC will be moving a lot – having no sudden accelerations, but still moving. Over a long period, this could potentially excessively flex the cables.

So how was the PC support system made? Firstly, we folded up some brackets from aluminium sheet.

These were bolted to two panels of laminated particle board that sat snugly in the spare wheel recess. The particle board both locates the brackets and also provides good support. In this view – from underneath – you can see the particle board that bolts to the original spare wheel cover, which in turn has the carpet sandwiched between the cover and the brackets.

The rubber balls were glued (using high strength, quality brand superglue) to the brackets as shown.

The PC sat on these balls, being glued to them with more of the high-strength super glue. (This glue works very well at joining rubber and metal.)

Fore/aft movement (forwards movements is strongest in a car – that’s braking) is prevented by the shape of the brackets and the compression of the balls, which are placed not only under the PC but also partly towards the sides. However, there’s nothing in the bracket design stopping lateral movement. To prevent this, acrylic strips were heated and bent so that small arms projected upwards at each end of the PC, preventing excessive movement in these directions. The arms have an in-built ‘springiness’ and so the PC doesn’t ever hit these with a crash.

The cables were left fairly long so that they could easily move with the PC – the longer they are, the less tight a bend they have to follow. Note that while the central location in the boot looks poor from a packaging perspective, one of the criteria involved in its placement was that a pram still had to fit in the boot. Putting the PC here allowed that to occur. If you expect a lot of luggage to be going in and out of the boot, it pays to put a shield over the cables and their plugs.

Mounting the Track Ball

As mentioned earlier in this series, the pointing tool can be either a touch-screen LCD (best), a trackball (good) or a joystick running mouse software (potentially good but we haven’t tried it). In this install we’re using a trackball. The trackball was purchased from Jaycar Electronics for $30.

It was screwed to a disc of plastic that was then installed in the front of two cupholders. In use, the thumb (either left or right hand, allowing the passenger to operate it as well) rolls the trackball while the main mouse button is operated by the forefinger that curves through an opening under the ball. It works well because the design allows operation without looking – the hand folds around and through the device. A normal PS2 extension cable was used to connect the trackball to the PC.

Here the easy access to the trackball from both front seats can be seen.

Windows Options While in this series we’ve concentrated on the installation side of the hardware, how you configure the software will make a major difference to how easy it is to use the PC. For example, under Display Properties in Windows, there is a wide variety of Appearances that can be selected. These include Windows Standard, High Contrast and many others. The font and icon sizes can also be changed. Selecting a large font, high contrast, default appearance will result in the small LCD screen being far easier to read in a car.

Conclusion

This series has shown one way to install a PC in a car. We chose to use a mains inverter, FM modulator and mount a conventional PC on an air suspension system. In addition we used a small trackball and a 7-inch LCD screen. Along the way we needed to build a noise filter and a new power supply for the LCD – both to reduce noise in the audio. We also used a secondhand PC with quite limited processing power and hard drive space.

But we’ve shown only one approach. Instead you can for example use a dedicated 12V PC power supply to provide power, a touchscreen LCD to act as both display and pointing interface, and feed the audio output into a dedicated amplifier.

And of course, with a faster PC with more RAM and hard drive space, you can run far more applications – stuff like DVD, voiced navigation, and lots more MP3 tracks. (And in fact that’s exactly what we intend doing later in a second system.) But whatever the final in-car PC iteration, you’ll need to organise a power supply, screen, audio output and pointing device.

The result? In-car capability that can only be dreamed of with conventional car systems.

Boot-Ups and Shut-Downs The PC uses an inverter to drive its power supply. As described in Mains Power For Your Car , the inverter is fed DC power through a heavy-duty relay that is turned on and off with the ignition key – they relay is powered by an ignition-switched voltage. So when the car is started, on comes the inverter. It’s possible to configure the PC so that when it’s fed mains power, it automatically boots up. Some motherboards have this option built into the bios, or you can use the trick shown in Silicon Chip where a capacitor and resistor are wired at the PC switch. We did the latter. Shutting down is more problematic – we’re exploring some options but at this stage it’s done manually using the trackball and screen.