So far in this series we’ve covered an overview of installing a PC in a car
, getting audio into the car’s original sound system
, and installing
a suitable LCD screen
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
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
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!
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
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
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
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 OptionsWhile 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.
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
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
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
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
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.