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Topic: Speed sensor (Read 5 times) previous topic - next topic

mowcius

Nice, I will have to try that some time...

Mowcius

Sweeduino

looks great, cant miss that even if i tie the laser to a lamp post. Now I'll just need to find solar panels. (Right after these messages... Implies that I'm taking a break now to go to sleep.)
Thanks a lot for all the help! If, (I'd like to say when), this idea becomes real I'll be sure to post it here.

/Ulf

Everett

You didn't say what type of reflex (reflector) you have across the lane from you.  If it is the usual safety reflector, then it should be forgiving of vibration.  Most safety reflectors use the "corner cube" principle. This sends light almost directly back to the source, regardless of the incoming direction of the light.   I just tried this with my pocket laser and the reflector on my bicycle.  The light does not come back in a pencil beam, it is spread out a few cm, but does come back very close to the laser pointer.  Maybe a better quality reflector would have a tighter return beam?

I think you could make this work with the laser aimed at the reflector across the lane, and something like a 5 cm by 5 cm solar cell directly behind the laser pointer, maybe with both inside a 10 cm dark plastic tube to block stray light.  The solar cell should mostly ignore (integrate) flickering in the return beam.  

Here is another idea, what if the time it takes a car to pass a single sensor is long compared to the time of the flickering?  You could program to ignore the quick on and off events and only record data when the blocking was over a certain minimum time interval.  This would reduce your timing accuracy (jitter) and would set an upper limit on the speed you could measure.

Sweeduino

I've just ordered the solar panels, they're 2,5cm square. So in a week or two they should arrive and by then i hope to have some code to test them with. Stay tuned...

/Ulf

mowcius

Cool, I look forward to hearing about it...

Mowcius

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