Thread: Another E46 carputer

Hi guys, this is my carputer installation. The installation is pretty straightforward and doesn't involve bondo or paintwork, just some sawing and epoxy. It is mostly done and there's no active development for months, but as usual there are always space for improvement. Enjoy!

This is my first post on this forum, hope I'm not breaking any rules..



Specifications
Processor : Intel Atom processor D410
Number of cores : 1
Clock Speed : 1.66GHz
Memory : 2GB DDR2 SDRAM 800MHz
Graphic : Onboard - Intel integrated GMA 3150
Sound : Onboard
Hard disk : Seagate 5400 60GB

1 Construction

1.1 CPU Power supply

Powering the CPU motherboard is M3-ATX. In picture below, M3-ATX is on the left while on the right is PicoPSU-80.



1.2 CPU

The Intel D410PT has the single core Atom processor soldered and passively cooled, onboard graphic with VGA out, 10/100 LAN, sound, 8 USB, SATA for hard disk and serial headers.



Case is M350




1.3 Monitor

The monitor comes off eBay from China. It has two composite inputs and a VGA and reverse camera trigger. Unsurprisingly, during disassembly I found out that most of the monitor components are held together by hot glue..



1.4 Amplifier

Driving the speakers is a home made amplifier with TDA7560 quad 4x45W bridge amplifier. It is built so to use the remote wire feature from the power supply. Some construction pictures.













1.4.1 Ground loop problem

There was a lot of CPU and hard disk noise in the first revision of the amplifier. Turns out the problem is ground loop between the computer and the amplifier. Combating this, the loop was broken by separating power and signal noise with a 10ohm resistor.

Quote from http://ludens.cl/Electron/audioamps/ta8215.html

If you compare this schematic to the one in Toshiba's data sheet, you will notice that it's almost an exact copy, except for R3! Toshiba ties the input ground directly to the output ground. In a PC, this leads to trouble! A computer is a noisy machine. There are quite strong noise currents circulating through ground, for example. If you tie all grounds together, it could well happen that a noisy power ground return from the hard disk takes a route through this power amplifier and the sound card! This makes some nasty noise show up in the speakers.

It's important to understand that the TA8215, like many such chips, has the preamplifier internally separated from the power amplifier. This is very useful to get rid of the described ground loop problems! I left the input ground separated from the output ground, except for the 10 Ohm resistor. If you happen to use this amplifier with a signal source that has a floating ground, the resistor is low enough to apply proper power ground to the preamplifier stages, and it works well. But if you install the amplifier in a PC, the 10 Ohm resistor is high enough to break up the ground loop that would otherwise form! All sensitive input points, such as voltage divider grounds, feedback returns, and ripple filter capacitor ground, are directly connected to the soundcard ground, and separated by the resistor from the power ground. The result is a very good rejection of noise. In my system, I can't hear power supply noise at all, but if I short out the resistor, the noise is all over the place!

1.5 IBUS interface

IBUS interface was built with the KBUS tranceiver IC (Melexis's TH3122) bought from reslers.de. It is the serial/rs232 version of it. A minor correction was made to Rolf's schematic on the max232 portion. Also the NTSC wire was omitted.

Rolf's schematic


from Maxim's datasheet


Construction pix











Navcoder showing whats happening on the IBUS


1.6 Wiring harness

For this, the 17 pin to ISO radio connector was bought for cleaner install. Wiring harness include a 22000uf 25V cap and 10A fuse. The wires are all salvaged from broken ATX power supplies.







1.7 Bezel

The bezel is from Janus. It is actually designed for double din radio so a little modification/hack is expected. I chose this over the TFT bezel because this is cheaper. The LCD is held onto the frame with epoxy.









1.8 Software

The computer runs on Windows XP PRO SP2, there are two frontends that I'm currently evaluating, Centrafuse and Riderunner.

Windows installation through USB thumbdrive


Desktop


Centrafuse


Riderunner with Simplistique V0.3 skin


1.9 Putting it all together

Mock up


Cramming all in, amplifier sits behind the screen while the CPU will be in the glovebox




CPU was moved to underneath the glovebox later