Issue
143 June 2002
Invisible
Components
by
Ed Nisley
What you can’t see can hurt you—at
least in the analog domain. In this article, Ed flags
all of the hidden obstacles you’re likely to encounter
on the road to building a trouble-free bicycle headlight.
This project goes nicely with Ed’s earlier instruction
on building a taillight.
Start
•
Directed Lighting • Battery
Basics • Down The Drain •
Invisible Resistors
• Sources
& PDF
This
year, my wife Mary decided to begin her bicycle commuting
season in March, rather than waiting for Daylight Saving
Time to kick in. She normally leaves work around 5:30
p.m., near sunset, which means she needed good lighting
for her four-mile ride.
The
large LED cluster I described in my column last April
(Circuit Cellar 129) serves admirably as a taillight,
but what makes a good headlight? Many years ago, I built
a PWM brightness controller for an automobile headlight
powered by a motorcycle battery, a bulky and corrosive
way to go, but it worked wonderfully.
After
considering the options for this project, I chose simplicity
and reliability over fancy features. Photo 1 shows what
half an hour pondering the stock at the local Home Depot
plus a bit of rummaging through my parts heap produced.
A handful of 2² Schedule 40 PVC fittings house a halogen
spotlight and a switch, powered by a sealed lead-acid
battery with an automotive blade-style fuse.
All
of the parts that could cause trouble are conspicuously
absent. Lacking a brightness control, voltage step-up
or step-down circuitry, fancy LED status indicators,
and without a single microcontroller, what can go wrong?
Alas, it still requires wires, connectors, and a filament.
In
the analog domain, however, it’s often the components
you can’t see that give you the most trouble. Let’s
take a look at some considerations and, along the way,
discover why schematics don’t tell you everything you
need to know.
