On Thu, 04 Mar 2010 10:27:43 +0000 Jonathan Gazeley <jonathan.gazeley@xxxxxxxxxxxxx> wrote: > 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. Instead of directly trying to measure RPM, measure milliseconds per rev. then invert it. Once you have your first reading, then start to average over 2/3 revs. gives you a pretty fast responding figure with a simple setup. Also, use a short range photocell on the spokes (say 50mm). Easy to mount, reliable results with minimal effort. As these can usually respond up to 10-30kHz you won't have to worry about pedalling too fast :) -- Will J Godfrey http://www.musically.me.uk Say you have a poem and I have a tune. Exchange them and we can both have a poem, a tune, and a song. _______________________________________________ Linux-audio-user mailing list Linux-audio-user@xxxxxxxxxxxxxxxxxxxx http://lists.linuxaudio.org/listinfo/linux-audio-user
