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

[Jason Plumb]

Paul Stoffregen wrote:
> Steve, if you were to get some of those hoses (that work mechanically), 
> especially if they have the bell dinging thing, I'm pretty sure a sensor 
> could be connected that would give a pulse that could be counted by an 
> Arduino or other microcontroller board.  Since the pulse rate is pretty 
> slow (less than 500 Hz), it'd be pretty easy to count the pulses using 
> polling or the pin change interrupt.

This seems like the most straightforward and, ahem, natural approach.

I'm pretty sure I've seen those hoses strung across the bike/ped path on 
the Hawthorne bridge, so they probably are capable of being triggered by 
bikes.

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?

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?

-jason