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From: Kai-Martin Knaak <knaak AT iqo DOT uni-hannover DOT de>
Subject: Re: [geda-user] Best way to measure RPMs
Date: Thu, 23 Jan 2014 00:06:59 +0100
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Rob Butts wrote:

> The application is an arm bicycle where the spinning shaft is connected
> to a handle on each end so with no gearing the rpms will not be too
> high.  I don't have any encoder yet and I can attach anything to the
> shaft.

There is a spinning top experiment in the physics lab at my day job. We 
attach a little magnet to the wheel and put a pick-up coil from an 
electrical guitar in the sensor. A comparator turns the signal from the 
coil into TTL compatible form. This gets fed to a digital multimeter with 
frequency input.

The set-up works nicely from up to 3 cm distance. And it proved to be 
student safe since 3 semesters :-)

---<)kaimartin(>---