[dorkbotpdx-blabber] Fwd: [freegeek-social] Bike Counter for WNBR -- ideas? volunteers?

subbies at redheadedstepchild.org subbies at redheadedstepchild.org
Wed May 28 22:40:44 EDT 2008


wellllll, you could even throw in the last 
colored-sticker-on-helmet-for-Processing in tandem with my idea 
(making it colored sticker on helmet with number) and thereby try *three* 
out all at once.
-Alexis

+ --------
   redheadedstepchild.org
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On Wed, 28 May 2008, Donald Delmar Davis wrote:

::How about we pick 2 methods (ground sensor image processing) with alexis's
::sticker idea as a control mechanism and implement them.
::
::Document the results.
::
::
::Management. We need some management here.....
::
:::)
::
::On May 28, 2008, at 10:23 AM, Mykle Hansen wrote:
::
::> 
::> On May 28, 2008, at 7:42 AM, Jason Plumb wrote:
::> 
::> > I've always wondered how those things work and what the response rate is
::> > like.  Do they really just give an on/off or are they using a summing
::> > pressure system of some kind?  Are they *really* capable of detecting when
::> > two cars/bikes pass over very *very* close together?  Just given the
::> > number of cars on the road, isn't there a pretty high statistical
::> > probability that two will hit in the same millisecond (or lower)...so how
::> > do *they* handle it?
::> 
::> i don't know exactly how, but here is a paper from 2002, in which
::> NZ traffic engineers tested some of the tube devices on the market
::> for counting both cars and bikes:
::> 
::>   http://www.ipenz.org.nz/ipenztg/papers/2002_pdf/34_MacBeth.pdf
::> 
::> i worry, tho, that with their sample size of 50 bikes they're
::> not close to hitting the level of traffic we're expecting.  on the
::> other hand, it's all about the sample rate ... not just the chip,
::> tho, it's also limited by the properties of air in a tube.  but
::> if the rate is high enough, it ought to be able to reduce this
::> problem to an acceptably low level.
::> 
::> > At 15mph, bikes wheels spaced 1.3cm apart will hit the sensor within 2ms
::> > of each other (hitting Paul's 500MHz example).  1.3cm ain't big, but it
::> > also ain't tiny.  I could see this happening in reality....so the question
::> > is, what do you do with the missing/bad counts/anomalies?  Is it ok to
::> > drop somebody?
::> 
::> one option is to funnel the ride through some narrow counting
::> point where the possibility of side-by-side riders is lower,
::> and lay the tube there.  another is to use multiple counters
::> in multiple locations and average the results.  (i was going
::> to suggest running a group of tubes at different angles, until
::> i imagined riding over that naked. =)
::> 
::> -m-
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