Electronic Design

Car PC, Part 1: Car2PC Adapter

I used to get under the hood of my first car to do everything from changing the plugs to adjusting the timing. That is not practical these days, as the number of microcontrollers in the typical car has grown dramatically. They now handle everything from motor control to the locks and windows in the doors.

Some enthusiasts still attempt to customize their cars at this level, but most forego such critical modifications. One area where you can make modifications is in a car's telematics system. This includes things such as the radio and navigation systems.

This article is the first in a series about customizing your car for use with a PC. It will allow operations such as MP3 playback as well as features included in the navigation system. Most of these are available as options on new cars and they can also be added after the fact. Dealers and plenty of third parties will be glad to separate you from your cash for some spiffy new products.

Of course, there are two reasons you might want to take another course of action: price and features. The former is not guaranteed, but usually doing your own installation can save a good deal of money.

This project addresses a number of different components. The first is the Car2PC. This module sits between the typical head unit (i.e. car radio) and a PC. Subsequent articles will address the PC portion, including an embedded system based on a Mini-ITX motherboard from ITOX Applied Computing.

Anyone can drop a laptop in the passenger seat, but that laptop's speakers don't compare to even the cheapest car speakers. Likewise, changing tunes on the laptop while driving tends to be hazardous to your health.

Car2PC (Fig. 1) is one way to connect the laptop to the head unit in a wide range of cars. InDashPC is the distributor for Car2PC. You can check their site to see what cars are supported. This project used a 2000 Honda Odyssey. The unit runs about $89. Price depends upon the car's manufacturer. Therefore, the cost may be a little more or less—it all comes down to your needs.

The Car2PC comes with an adapter cable (Fig. 2) that connects the head unit to the Car2PC module. This plugs into one end of the Car2PC module (Fig. 3). The custom USB cable (Fig. 4) plugs into the other end of the module. This cable plugs into a PC's USB port and audio output ports.

Car2PC sends the PC's audio out through the car's speakers. It is under the head unit's control so you can control the volume, etc., from the head unit as usual. Car2PC detects the state of the head unit and can send back key events to the PC. In particular, the six speed selection buttons are used to select one of six playlists.

Installing the Car2PC hardware
The installation in the Honda Odyssey took about half an hour, not including photos, and only required a pair of screwdrivers. The hardest part was finding the instructions on removing the dashboard from around the radio. The general process will be the same for most vehicles, but check before you start.

I started using a small, flat head screwdriver covered with a cloth to pop up the bottom edge of the dashboard cover. At this point, it could be easily removed (Fig. 5). Closely looking at the brackets (Fig. 6) and the holes (Fig. 7) shows that they will easily pop in and out. There are ten bracket and hole pairs spaced around the cover.

There was a pair of switches and the climate control system still attached to the cover. The cables to the switches were easy to release and allowed the cover to be flipped up (Fig. 8). This way, I did not have to disconnect the climate-control system.

The four mounting screws around the radio were now accessible (Fig. 9). The unit slides out with the tray underneath once the screws were removed (Fig. 10). This exposes the main cable that connects the radio to power, speakers, and the antenna (Fig. 11).

When you take a closer look, you will see two connectors on the back. The second is where Car2PC cable is plugged in (Fig. 12). It is also time to plug in the USB cable (Fig. 13). The Car2PC unit is small and fits easily behind and below the radio. There is also a small hole where the USB cable is able be routed to the glove compartment (Fig. 14).

The glove compartment routing was handy for my initial testing with a laptop. I added extension cables for both the USB and audio connections. This allows the laptop to sit on the floor or on the passenger side seat. At this point, it was time to test the software before securing the cover back over the radio.

Car2PC Software Installation

Car2PC comes with software support for Microsoft Windows and most Palm handheld devices. The audio connection can be used by any device, such as an iPod or other MP3 player. However, the Car2PC tends to be overkill for that alone. The main benefit is the ability to provide control feedback to the PC.

I tested the system using Windows XP on my laptop. Windows goes through its normal device driver gyrations when the Car2PC is plugged into the USB port. The device driver is found on the Car2PC installation CD. Afterwards, the USB device shows up in the Windows Device Manager (Fig. 15).

The next step was to install WinAmp, included on the CD, and the Car2PC plug-in. There is a matching plug-in for Windows Media Player. With both of these, you can select six playlists (Fig. 16) that will be accessible when pressing one of the six buttons on the head unit. Only one of these applications should be used at a time, but typically a user runs only one of these anyway.

After selecting six of my favorite playlists, I set the laptop aside. Listening to a playlist was simply a matter of selecting the CD from the head unit and then pressing one of the buttons. The applications usually remember the last song being played, so you can switch between playlists whenever you like.

The Odyssey has a channel select and volume control located on the steering wheel. As expected, the channel-select button switches between songs within the current playlist. Now it is a snap to listen to songs and a good bit safer when driving as well.

The next article in the series will be on the construction and installation of the IOTX Mini-ITX computer. Initially this will be a headless configuration that works with the Car2PC. Till then.

Related Links


ITOX Applied Computing

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