Mike A Schwab writes:

On Wednesday, March 13, 2019 at 10:52:57 AM UTC-5, Radey Shouman wrote:
Mike A Schwab writes:

Here is a great article by Sheldon Brown showing how bicycle
cyclometers work. When bladed spokes came out, some units would
register twice the distance at slow speed up to 6 mph 10 kph, so it
can give you an idea of how fast it can register the magnetic field
closing and opening a reed switch in the pickup.

https://www.sheldonbrown.com/cyclecomputer-magnet.html

That does seem to show that, at least at slow speeds, on a high-end
computer, every reed switch pulse is used to compute a new speed. It's
not clear whether the computer fails to register a double pulse at
higher speeds, or that the internal algorithm changes. Either one is
possible.

Here is a bicycle handlebar bubble inclineometer if you are still
interested.
https://www.amazon.com/Sun-Company-C.../dp/B06XCMXRVP

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OK. 10,000 meters per hour / 3600 seconds per hour gives 2.78 meters
per second. A 700c road tire is about 2.1 meters per revolution, so
1.3 revolution per second. The width of the gap between the magnetic
field has to be under 10 MM 0.010 M so 0.013 second minimum time
without magnetic field to detect gap between the two sides of the
magnetic field. So 100 hz detect frequency???

When I threw out 100 Hz I was imagining a solution based on software
interrupt handling -- that was a WAG, and I doubt that's actually what
is used. I would pick a micro with hardware encoder input that can be
configured to count step and direction, so everything happens in
hardware. 13 ms is a long time in that case.


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