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An Active Brake Light Check Control: A Design Example

AN ACTIVE BRAKE LIGHT CHECK CONTROL
A DESIGN EXAMPLE

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This is a project for someone interested in the design and programming of aftermarket, automotive microcontrollers, or who might like to improve an important bit of his car.

Many BMW E36 3-series (from 1990–1998) came with a Check Control system that monitors most of the exterior lights and warns when any have failed. This includes the brake lights, and the brake light switch which inevitably fails with a BRAKE LIGHT CIRCUIT error. Here, you will find the complete details of a next-generation, active, check control system that only monitors the brake light switch and lights, but tries to solve this annoying problem.

first_installThe complete design, hardware and software, is ready for action in any E36 that did not come with check control, including the E36 Compact and Z3. It should also work in any car with European-style, rear turn signals, incandescent brake lights and a traditional, high-current, brake light switch. The hardware, omitting check control, is ready for adaption in a car that already has it.  The design should both prolong the life of the brake light switch and increase the speed and reliability of the brake lights.

Clicking the next three icons will download the complete design, with documentation.
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A ZIP archive (68 kbytes) of the check control schematic and circuit board, created with the Eagle PCB layout program, version 4.15. Freeware versions for Linux, OSX and Windows can be downloaded from Eagle's maker, Cadsoft, Germany.
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A ZIP archive (56 kbytes) of the check control’s C-language source code.
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A 14-page, PDF design review (928 kbytes) discussing the check control’s hardware, software and general installation. The review omits the nitty-gritty details of its first installation in a BMW 318is. The author can write those up, should anyone get that far.

The check control's power supply circuit appeared as an
Idea for Design in the 23 October 2007 issue of Electronic Design magazine.

Copyright © 2007–2008 by John Firestone