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From: Jeff Liebermann <jeffl@cruzio.com>
Newsgroups: rec.bicycles.tech
Subject: Re: Garmin altitude problems
Date: Sat, 09 Nov 2024 14:14:08 -0800
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On Sat, 09 Nov 2024 21:11:17 GMT, cyclintom <cyclintom@yahoo.com>
wrote:

>On Tue Sep 10 03:33:23 2024 Jeff Liebermann  wrote:
>> On Mon, 09 Sep 2024 23:18:56 GMT, cyclintom wrote:
>> 
>> You're still replying to a month old article.  
>> 
>> > On Fri Aug 9 10:44:09 2024 Jeff Liebermann  wrote:
>> > On the right side of a Garmin 830 is a perhaps 2 mm hole, I assume this
>> > goes into a weather tight chamber where rathger than a diaphram detector
>> > it uses a silicon sheet suspended over the detrector which flexes with
>> > pressure. It is an analog device whick probably limits its accuracy But
>> > climbing a 10% slope it changes every one or two pedal strokes. by one
>> > or two feet. So it is pretty sensitive.
>> 
>> Mostly wrong.  The MEMS sensor can be piezo-resistive or capacitive.  Both 
>> are analog, are amplified on the MEMS device, and are digitized on the 
>> MEMS device to a common communications bus, such as I2C.  I haven't found 
>> autopsy photos for the Edge 830 so I'm not sure what the device might be.  
>> My best guess(tm) is this LPS28DFW piezo-resistive device:
>> <https://www.st.com/resource/en/datasheet/lps28dfw.pdf>
>> 
>> Is an absolute pressure accuracy of 0.5 hPa in a 24 bit word sufficient 
>> accuracy?
>> 
>> If the pressure changes every "one or two feet" (which it doesn't), do you 
>> have something against using averaging to smooth the data?  At sea level, 
>> pressure changes about 0.03 hPa/inch.  You might see the change, but it 
>> will be buried under the 0.32 Pa noise level. 
>> 
>> I seem to remember posting most of this information previously for your 
>> benefit.  
>> 
>> Posted with Pan for Linux 0.155
>> 
>> -- 
>> Jeff Liebermann                 jeffl@cruzio.com
>> PO Box 272      http://www.LearnByDestroying.com
>> Ben Lomond CA 95005-0272
>> Skype: JeffLiebermann      AE6KS    831-336-2558
>

So, why didn't you include a link to the article?  Couldn't find a
link?  Couldn't figure out how to do it?  

>Piezo resistive?

Yes.
<https://en.wikipedia.org/wiki/Piezoresistive_effect>
"The piezoresistive effect is a change in the electrical resistivity
of a semiconductor or metal when mechanical strain is applied. In
contrast to the piezoelectric effect, the piezoresistive effect causes
a change only in electrical resistance, not in electric potential."

The sensor that I GUESSED was used in the Garmin Edge 830 is
piezoresistive:
<https://www.st.com/resource/en/datasheet/lps28dfw.pdf>
"The LPS28DFW is an ultra-compact piezoresistive absolute pressure
sensor which functions as a digital output barometer."

>Why are you talking continually about things you don't know about?

Because you are continually asking dumb questions about things you
know that are wrong.  I consider that worse than knowing nothing about
a topic.

>You still haven't told us how you think a TV90 ground faulr detector works.

That's because nobody asked me how it works.  The Tektronix or Tempo
TV90 is not a ground fault detector.  It's a TDR (time domain
reflectometer).
<https://www.atecorp.com/products/tektronix/tv90>
<https://www.aaatesters.com/tempo-cablescout-tv90-catv-meter-model-cablescout-tv-90-tempo-90.html>
No PWM is involved.

You haven't told "us" why you answer questions, ignoring the answers,
and then attempt to change the topic.  One might suspect that you are
asking questions to waste peoples time so that nobody would see that
you are clueless.

>Shouldn't you be out riding a mile on a junk bike in order to prove you're a cyclist and deserve the right to tell us all how to ride?

As usual, you're mostly wrong.  You got the "junk bike" correct.  I
fished the frame and some attached components out of a dumpster.  I
replaced a few components, cleaned it up and replaced all the rubber
parts.  It currently lives in a plastic bag on my deck.  Old photo:
<https://www.learnbydestroying.com/jeffl/pics/bicycles/Gary-Fisher-Tassajara.JPG>
My other bicycle is not quite as bad.  I bought it new in about 1986:
<https://www.learnbydestroying.com/jeffl/pics/bicycles/Miyata-610.JPG>
Notice the downtube friction shifters.

I'm not trying to "prove" that I'm a cyclist.  Currently, I can ride
about 4 or 5 flat miles without back pains.  That's lousy, but better
than it was in previous years.  I had planned to try longer rides this
summer, but was interrupted by some medical problems and because it
was too hot.  I'll try again next summer.  

As for my "right to tell us all how to ride", I don't give riding
instructions.  However, since you're asking me for permission, I
hereby grant you and "us" permission to ride in any manner you both
find appropriate.


-- 
Jeff Liebermann                 jeffl@cruzio.com
PO Box 272      http://www.LearnByDestroying.com
Ben Lomond CA 95005-0272
Skype: JeffLiebermann      AE6KS    831-336-2558