Hi All, I'm looking for a part which provides an output signal when a reflective surface is placed in front of it. I'm designing a circiut for my kids in which an LED should go on everytime their hamster makes one revolution in it's spinning wheel. Thanks in advance for your help!
-Jen
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.
Temecula CA.USA
"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
Thanks! That's a neat idea, if I can get it to work. It also would demonstrate to the kids how mechanical energy can be turned into electrical energy.
-Jen
Thanks for the idea! If the first solution posted here doesn't work, than I have a backup.
-Jen
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,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
One could probably just buy a bicycle speedometer and use it directly. They should have calibration instructions, and you could probably calibrate it so that 1 revolution gives a reading of 0.1 or 0.01 miles, making it easy to figure the number of revs from the odometer reading.
Mark
a maget's going to unbalance the wheel (easily cured) but also cause a non-uniform drag and a cogging action when it passes near the steel axle supports, dunno if that'll trip the hamster up or not.
a piece of retro-reflective tape would probably work well if cleaned regularly.
Bye. Jasen
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