How to measure length of an object approx 10cm long within +-1mm by non-contact method, e.g modded flatbed scanner?
I currently am using a laser beam mounted in moving carriage of a hacked inkjet printer. When beam is broken carriage stops and stepper motor steps are counted. However this method is ugly and slow.
Something like a glass surface I can place the objects on (such as base of a hacked flatbed scanner) would be much better and wipe-clean. By lining object up in same direction each time, only one row of pixels would need to be read for example looking for a sudden change of contrast. Cannot find any way to easily intercept output of a scanner on the web however, especially a more manageable single pixel as it scans across the length of the scanner.
Alternative might be photographic, for example camera mounted under the glass surface, or even a moving camera to eliminate parallax error.
Any suggestions gratefully received no matter how crazy.
Thanks in advance,