Magnetic or photoeye encoder?

[Armored Cars]

Does anyone know of a good encoder that reads off a spinning magnet like on a bicycle?·
I also wanted to know if a photoeye placed very close to a spinning disc·with holes in it could work as a crude encoder.· A bright LED could be placed on the other side to help distiguish light from dark.· I dont know how photoeyes work, and was wondering if·they would lag at high speeds and not get good readings or not.

[Jon Williams]

You could use a Hall-effect sensor with a magnet, and a photo-transistor with your LED scheme. If using the BASIC Stamp, the COUNT instruction can be used to determin wheel speed.

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Jon Williams
Applications Engineer, Parallax
Dallas Office

[Armored Cars]

I found it... very small, lightweight, and only $10:

http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXFVF5&P=7