UnofficialBMW.com
An Active Brake Light Check Control: A Design Example
AN ACTIVE BRAKE
LIGHT CHECK CONTROL
A DESIGN EXAMPLE
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.
The 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.
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.
A ZIP archive (56 kbytes)
of the check
control’s C-language source code.
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