[LAU] A crazy idea

Jonathan Gazeley jonathan.gazeley at bristol.ac.uk
Thu Mar 4 05:27:43 EST 2010

On 04/03/10 10:20, James Morris wrote:
> On Thu, March 4, 2010 09:48, Jonathan Gazeley wrote:
>> 1. A sensor that can measure my cadence. A simple magnet switch that
>> triggers once a revolution won't be enough to measure the cadence with
>> sufficient resolution, since my cadence is usually between 50 and 80
>> rpm. I would probably need to mount multiple magnets spaced equally
>> around the chainwheel and have a single sensor on the frame. Then I have
>> to get it to supply this information to my control program.
> Cycle computers which measure cadence work with a single magnet on the
> crank and can measure cadence in that range and above. I think the fastest
> RPM I ever got was (only a vague memory) around 120 (maybe?) when I was
> being silly trying to see how fast I could pedal.

Yes - I have a cycle computer that can measure cadence. However, I 
typically pedal between 60 and 90 rpm which means my reading would only 
be available for sampling every 0.7 - 1.0s. It would work, but in the 
space of one second my cadence can vary a lot if I'm accelerating so the 
sound of the rising revs would be jumpy.

Also, if I suddenly stopped pedalling, it might take up to a second for 
the sampler to register and kill the engine noise. I don't think it 
would be a very satisfactory experience, which is why I was thinking of 
mounting 10 or so magnets around the chainwheel, to be able to sample 
the cadence every 0.1s.

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