..Is it correct that you're using the dark/light contrast to find the position of a boundary between dark and light parts of an image?
How accurately can you position the sensor? Is it feasible to scan the sensor across the boundary? If so, I suspect you could get a much more precise position for the boundary by interpolating the position of the '50%' brightness point from a sequence of brightness readings in different positions rather than needing a single brightness reading to give you a hugely precise measurement of the proportion of dark/light areas within the image.
As mentioned, 0.01mm per integer from the ADC is adequate, but 0.1mm isn't.
QuoteAs mentioned, 0.01mm per integer from the ADC is adequate, but 0.1mm isn't.I don't know what exactly you are trying to achieve but 0.1mm seems to be well below what a (untrained) human eye can detect.Maybe you want to step back and see the minimum resolution / accuracy required and what that corresponds to a voltage signal for your adc and go from there.
I don't know your setup that well but if you are using dividers or voltage references, think about what kind of resistors /Vref you will need in order to maintain the comparability of 16-bit adc from source to source.
It sounds as if, as well as being at the limit of how accurately it's feasible to measure an analog signal, you're also at the limit of how frequently you can take those measurements. This is not encouraging, and you may be constraining yourself into an intractable problem. I still feel that using a single brightness reading requires that reading to have unrealistically fine resolution and interpolating from multiple readings would enable you to get a better resolution. One way to relax the precision requirements would be to reduce the size of the scanned area. That would mean you have even stricter requirements to get the scanner positioned in the right place and I don't know whether that's feasible.Is it possible to give a more general explanation of what you're trying to achieve and what overall system this solution has to fit within? It may be possible to apply some lateral thinking, such as applying a vernier technique using multiple sensors, but without any idea what the thing is you're trying to measure the position of, it's hard to know where to start.
The only one I've had first hand experience with on a arduino is the TI ADS1115 16 bit 4 channel (or 2 differential channels). http://www.ebay.com/itm/4-Input-16-Bit-I2C-Analog-Digital-Breakout-Micro-Controllers-Arduino-/330761041957?pt=LH_DefaultDomain_0&hash=item4d02e4f825I have a check out sketch code available if you actual try one of these out.Lefty