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Old March 13th 19, 02:15 AM posted to rec.bicycles.tech
Frank Krygowski[_4_]
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On 3/12/2019 8:15 PM, Mark J. wrote:
On 3/12/2019 10:05 AM, Frank Krygowski wrote:

I'll note in passing that the original Avocet cyclometers use a tiny
(2"?) ring of 20 magnets to generate a wave signal using a coil
pickup. It's quite a bit different from the clicks of a reed switch.

IIRC, Jobst was in on that design. I doubt it's coincidence that he
also had done a lot of toying around with ancient Sturmey-Archer
dynohubs, which also use a 20 magnet ring, although a much larger one.

I've heard a rumor that the Avocet can get its signal directly from
the S-A magnets. But despite owning both, I haven't tried it.


I'll just note that I always thought those Avocets were using a
Hall-effect sensor rather than a coil.* I can't remember if I /knew/
that (perhaps from a Jobst post) or just guessed it.* Not sure if that
makes any difference, I suspect in either case the design was still just
counting magnets rather than sensing how fast they move past via ?the
shape of the current spike?


Here's a post
https://groups.google.com/d/msg/rec....k/tojDfIFAG0MJ
where Jobst mentions the Sturmey-Archer Dynohub powering the pickup.
Note his phrasing about "the pickup will have enough induced current."
I'm pretty sure that means it's just a coil, not a Hall effect switch.

--
- Frank Krygowski
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