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GPS Units = Show road steepness?



 
 
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Old March 15th 19, 02:11 PM posted to rec.bicycles.tech
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Default GPS Units = Show road steepness?

On Thursday, March 14, 2019 at 7:47:56 PM UTC-7, Mike A Schwab wrote:
On Thursday, March 14, 2019 at 10:17:21 AM UTC-5, Radey Shouman wrote:
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

--

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.


--


Well, actually the reed switch is effectively a relay. Takes 1/100 of a second to close in the gap between the sides of the magnet. Computer could be sampling much more often. And a faster speed doesn't give the reed switch enough time to close.


I would have to think about that for a minute. That appears to be a good idea. Microswitches are a quality control problem though I think that they would actuate better than 10 msec. In any care it wouldn't matter since 100 kph would be a maximum rotational period of, what, 72 msec.

Inductive switching would be inherently less likely to have quality control problems but it would also make the input circuitry more difficult to control since the rapid crossing of the coil by a magnet at high speed would generate a higher voltage signal and likewise lower speeds very little. So you complicate the input circuitry either by amplifying the lower speed inputs and then using a Zener or something to regulate the higher or visa versa. The problem here is that you're messing around with potentially destructive voltages around low voltage circuitry.

I would say that it's probably a tossup since microswitches are very old technology and manufacturing is stable.
 




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