Electronics Forum / Basics / April 2006

Hello Jen,

Here is one effective and interesting approach if you can get the
pieces to build it.

Someone in the group brought this to my attention a little while back,
I thought of mounting one on my backyard miniature 7' windmill.

http://www.freelights.co.uk/how.html

   * * *
Christopher

Temecula CA.USA
http://www.oldtemecula.com

"Jen"

** Try attaching a small magnet to the wheel and have it activate a reed
switch each revolution.

Then it's just battery, reed switch and LED -  plus maybe a resistor.

Reed switch  =  tiny, glass encapsulated, magnetically *closed* switch used
in burglar alarms to detect open doors and windows.

.......  Phil

I've been using Hanamatsu P5587 photoreflectors, which are designed
for exactly this purpose. They include LED and sensor in a single
5-pin package and have a schmidt-trigger and amp built in, so they
provide a clean 0-5V signal you can generally use without further
conditioning. They're popular with robotics enthusiasts for making
wheel encoders, which is what I use them for. I've found them to be
pretty sensitive to the distance between sensor and target though, and
need to be within a few mm with a fairly true wheel to work reliably.
That's using laser a laser printed patter with stripes 3-4mm wide
though, larger stripes and reflective material eases the positioning
requirements quite a bit. Even so, a hamster wheel may be a bit too
wobbly for them. If you want to try them, they're available in small
quantities from robotics enthusiast stores, www.acroname.com has them
for example. A search on the part name and 'robot' will find plenty of
examples and advice.

If you're not dead-set on an optical sensor, I think I prefer Phil
Allison's magnet and reed switch idea. Much less sensitive to
positioning and it won't stop working when the hamster flicks a bit of
sawdust on the sensor. Bicycle computers work this way, with a magnet
on the wheel and a reed switch on the frame.

Tim