On 28/10/2010 01:54, Youda He wrote: > On Wed, Oct 27, 2010 at 4:13 PM, Robin D. Bussell > wrote: >> Could you use the regularity of the window spacing on the train >> carriages to measure speed by detecting variations in reflected light? >> >> Send a modulated beam across the tracks at the right height and >> analyse what gets reflected back. >> >> Cheers, >> Robin. >> >> > The window transparency test sounds very interesting, can try that. > May place a simple light source and check the reflection, or just > using the light from inside to detect the light change, as long as we > know the size of the window, we should be OK. > > -- Youda > I haven't been following this thread too well (so ignore this if it's=20 already been ruled out for some reason), but from what I have seen I=20 can't help thinking something like the "clickety click" detector=20 (Ithink) Joe suggested would be the simplest way of doing this, hardware=20 and software wise. If you can place a cheap mic (preferably with a=20 filter) reasonably near the joins in the track then it should be no=20 problem. and pretty accurate - I imagine the mic would not even have to=20 be very near as long as it was directional. --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .