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Modifications

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In late 2001 the car computer was ready for daily use. Still, it was only a matter of time before some changes would have to be made. That time came sooner than I expected.

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Car

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After having driven it for 6 years, my old 1976 Buick Century bit the dust, in the summer of 2002. Rather than starting a new project for the 1997 Pontiac Bonneville, I kept the same computer and reused some of the car stereo components.

Car Stereo:

Prior to moving the system to my Pontiac Bonneville, I took the opportunity to address some problems that I encountered in my previous install:

• In the old system I had to swap RCA cables when switching between the computer, the CD changer, and the tape player. To avoid making the same mistake again, I decided to replace old tape player with a CD Player with an Auxiliary input. This eliminated the cable swapping, and added the ability to use the head unit to control the volume on the car player.
  
  
• In my previous install, I used a cheap AudioVox amplifier to power the front speakers. The frequency response left a lot to be desired. As a result, some heavy-duty eq'ing was required to get semi-acceptable sound out of the front speakers. Initially, I used the head unit to power the front speakers. Later, a new power amp was purchased so I could use the equalizer on the front speakers.

In addition there were some other things to account for when moving the car stereo system:

• The front dash speakers that I used in the old car won't fit in the Pontiac.
  
  
• Since the old Kicker Free Air's won't fit on the back deck, I built custom speaker boxes and mounted them in the trunk.
  
  
• After installing the car-player project in the old car, the CD changer was rarely used. It was a great backup system to use while the computer was down for maintenance, but the CD Player headunit will also accomplish this task. For that reason I chose not to install the CD Changer in the Pontiac.

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Construction

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Speaker Boxes:

With no good place on the back deck to mount the subwoofers, a pair of speaker enclosures needed to be built. The design needed to meet the following requirements:

• It must have an internal volume between 1.0 and 1.5 cubic ft.
• It must not block the pass-through between the trunk and the back seat.
• One side needs to be sloped to match the front of the trunk / back seat.

With that in mind I climbed in the trunk and took some measurements. I measured the angle of the back seat, which turned out to be 66 degrees. To avoid blocking the pass-through, the speaker boxes couldn't be any wider than 14 inches. The maximum height measured in at 14 inches.

To avoid nasty resonance problems I didn't want any of the dimensions to be identical. Also, I wanted a little bit of fudge factor when it came to height. For those reasons I changed the height dimension to 13 inches.

With the height, and front angle determined I found a javascipt-based speaker calculation page and start playing with the numbers. In the end, I decided on a trapezoid-shaped enclosure with the following dimensions: 13"H x 14"W x 15.25" D1 x 21"D2.

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Wiring

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Power Wire:

To power the computer, I ran 4 gauge wire direct from the battery to a distribution block in the trunk. To prevent fires and other mishaps an inline fuse holder was added, near the battery.

Then at the distribution block power is sent to the power amp and the computer. A relay was used to switch the computer on and off with the vehicle's ignition.

Turn-on wires:

Two remote turn-on wires were run. The first wire was run from the red "12V Switched" wire on the CD Player's wiring harness to the relay on the car computer. This wire is live when the car's ignition is turned on, but dead when the car is turned off. The wire doesn't need to be as heavy as the main power wire, because it's only used to trip the relay coil. This coil consumes a small amount of current. I used 18 gauge wire for this.

The second wire was run from the "power antenna" lead on the CD Player to the power amplifier's "remote turn-on" input. It's live when the CD Player is turned on, and is used to turn the power amp on and off. Since this wire only carries a small amount of current, 18 gauge wire was sufficient.

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OBD-II

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I ordered an OBD-II interface from ScanTool.net in the summer of 2002. The package included a interface board, a 25pin-to-9pin serial cable, and a J1962M connector. At the time, ScanTool.net didn't include pre-made cables, so I had to make my own using the J1962M connecter, some data cable, and a 9-pin connector. Since that time, they've made things easier by including pre-made OBD-II cables with their OBD-II kits. No case was included with this kit, but a quick trip to a local Radio Shack store took care of that. The OBD-II interface was mounted inside the dash.

OBD-II Cables:

The ELMScan VPW interface board has two connectors: a DB9M, and a DB25F. The "DB9F to J1962M" cable is used to connect the interface board to the car's OBD-II port. Then a "DB25M to DB9F" serial cable connects the interface board to a standard 9-pin serial port. Last, but not least, I made a "DB9M to DB9F" serial extension cable, and ran it to the trunk. This extension cable is identical to the LCD Serial Cable that I made when I first started this project.