I need to be able to read the distance to the floor at a range of about 40 mm, with accuracy less than 1 mm. It seems that, at such a close range, both IR and ultrasound sensors aren't of much use, and I don't think they would give me the accuracy I need. Is there another kind of sensor out there that would fit my needs?
Assuming that itis remote sensing and the whole thing has to be contained in a single unit then I would have thought IR return angle sensing was your best bet.
(disclaimer, never done this)
Check - http://sharp-world.com/products/device/lineup/data/pdf/datasheet/gp2y0a02_e.pdf -
If you would use the part of the curve on page 3 that is left of the peak 0-40 mm would give you a voltage between 0 and 1 volt. Using the internal 1.1V reference could give great accuracy. approx 40 mm in 1024 steps or ~25 steps per mm that gives you 4 bits for the noise ...
WARNING: Better use a 3.3V reference so the ADC allways can handle it. Would still give 8 steps per mm = 3 bits of noise.
Hope this helps,
Yes that is the sort of sensor I was suggesting:-
the distance to the floor at a range of about 40 mm, with accuracy less than 1 mm.
This only makes sense if the floor is flat to 1mm.
and the floor must be reflective ...
Well to IR, that sensor is not to fussy about that. It works off hands very well and you wouldn't consider them to be reflective.
Did you guys find anything about this subject?