Landrover ITX Computer
I have installed an ITX form factor PC into my Landrover Defender 90 along with a seven inch touch screen and a custom made relay interface with 8 outputs, 6 inputs and 2 analogue inputs.
The PC is a pretty standard ITX unit. The ITX motherboards are 17cm square and whilst they share most of their architecture with the larger AT and ATX form factors, they are designed to use Laptop components such as CF cards, PCMCIA cards etc. Some ITX cases are large enough to allow the fitting of standard PC hardware such as PCI cards and 3.5” hard drives. However, the ITX case that I am using, which has the same cross-section as a car stereo, is too small to accommodate standard components. Instead, it uses a 2.5” hard drive and a slot loading laptop style CD-RW/DVD drive. Tray style drives are also available. The processor is embedded on the motherboard but there is one slot to accept standard RAM (height can be a problem with small cases)
My ITX is spec’d as follows:
-Via Epia M1000 motherboard with onboard VGA, Composite video out, sound card, 10/100 networking, parallel & serial ports, USB and i1394 (firewire)
- slim slot loading combined CD rewriter and DVD drive.
- 2.5” 20 GB hard drive.
- 256 MB RAM
The pc has to have a specialised DC – DC power supply, this not only regulates the vehicle ~12vDC supply to the 3.3V, 5V and 12V required by the mother board, it also control the boot up and shut down of the pc. It provides a switching line, which basically become a remote on/off switch for the PC, which could be wired to the ignition, or like in my case to a separate switch.
The 7” touch screen uses USB for position data and comes with a specialised combined lead which is just long enough. Extensions can be sourced if needed. Its brightness is not the greatest but its one of the cheapest units around.
In order to survive engine cranking, the PC is powered by a second battery, which also powers all auxiliary lighting as well as the stereo and GPS. The second battery is charged via a voltage sensitive relay, or VSR, which is a great bit of kit, truly fit and forget, and no voltage loss like with diodes.
The sound output from the PC is connected to the aux in of a pioneer head unit which is capable of 4x50w. This is driving 2 6x9 speakers behind the rear bench seats and two 10cm co-axial speakers in the headlining.
The Garmin eTrex sits in its Garmin mount on the top of the dash. Its cable both powers the GPS, and provides serial data communication with the PC.
The relay interface unit is a home made custom built unit. Using the parallel port, it allows control of eight 12v relays (each rated to 25A) and has six 12v digital (~0v or ~12v) inputs. It also has 2 analogue inputs (0v to ~15v) for battery monitoring. These could be modified to be temperature sensors etc. The hardware consists of a couple of 8-bit tri-state buffers, 8-bit latches, two ADC chips, and opto-isolators to separate the PC from the vehicle.
The 8 outputs are ultimately controlled by a remote unit, which has a switch for each channel with on, off and PC control, this allows complete override if something goes wrong!
Examples of the 6 inputs include sidelights, headlights, reverse gear switch and a remote dash mounted button for use as a remote. The outputs are used for rear work lights, driving lights, and I have plans for an electrical engine fan inhibit switch for use when wading.
The software was written by myself in VB6, using a parallel port dll available on the internet. It controls the automation of functions such as the rear work light coming on when reverse gear is selected, or not, depending on my preference at the time, turning off driving lights when main beam is dipped, etc, it also plots battery voltage over time, and plays MP3s from a choice of the 2000 or so tracks on the Hard drive.