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Increase the resolution of IR distance detector


paulse

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Hello,

 

I see that the tinkerforge uses an ADC (12 bit range: Not Disclosed) converter on the IR distance sensor.  This seems to be a poor match with the performance specs on the sensor (http://www.sharp.co.jp/products/device/doc/opto/gp2y0a21yk_e.pdf).  Has anyone used a better ADC with this product?  eg.

 

For a 0-5 V ADC at 16 bit:

  • resolution = 5/2^16 ​​ V/bit = 7.6 x 10-5​​ V/bit
  • linear range of IR sensor document (i.e. 100 mm to 500 mm) =  50 mm / 1.55 V = 32.2 mm/V
  • so for 0-5V 16bit resolution ADC: the resolution should be 2.46 x 10-3​​ mm/bit

 

From this calculation the current resolution seems poor (maybe because tinkerforge is trying to save money and not concerned to much with resolution).  Even with a  0-5 V ADC at 12 bit resolution: (0.0407 mm/bit) 

 

Has anyone used a different ADC with the IR displacement sensor?

 

Thanks in advance,

Paul

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Thank you for the clarification, Borg.

 

Does SHARP provide a more in depth calibration curve than Fig.2 in http://www.sharp.co.jp/products/device/doc/opto/gp2y0a21yk_e.pdf ?

 

Something that indicates some sort of noise within the signal?  Say, something to quantify the precision and accuracy as detailed in the diagram below?

 

https://meettechniek.info/measurement/accuracy-images/definitions.gif

 

How is the digital signal converted to displacement?  Or is this all a black box that is only minorly detailed in the block diagram as the "signal processing circuit" of the PSD?

 

 

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There is no detailed calibration curve from sharp, the differences between the sensors are in the range of +-2cm full-scale depending on the distance in our tests.

 

We took one sensor per type and made a distance/voltage lookup table. You can find the table here (for the 2Y0A21 for example): https://raw.githubusercontent.com/Tinkerforge/distance-ir-bricklet/master/software/calibration/2Y0A21.txt

 

The Bricklet does a simple linear approximation with this table and does some averaging over the analog values to remove as much noise as possible.

 

You can upload a new table to the Bricklet if you want to calibrate for your specific sensor: https://www.tinkerforge.com/de/doc/Hardware/Bricklets/Distance_IR.html#verfugbare-spannung-distanz-abbildung

 

As far as i know there are no noise figures from sharp (which is a good indication that there is lots of noise).

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