max coordinates of resistive sensor

(This message was transferred over from our old forum)
Posted August 17, 2015
By Todd DeBoer
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On 4/5/10 TONYC asked, “What are the maximum coordinates of the resistive sensor for the 5.7″?
Is there any rescaling done when it is drawn on the display?”
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(Follow up post)

Answered:

On the LPC2478, two 10-bit A/Ds are use for the touchscreen sampling. They are then run through a calibration algorithm that maps the raw A/D values to the pixel coordinates. The A/Ds may only be seeing a range of 200-800 even though the full range is 0-1023, but I’d have to check again on what the exact range the A/D can report.

The FourWireTouchResist_TS.c sums 32 A/D readings and uses that as a 15-bit value, simulating an average of 32 10-bit values with a 5-bit fraction.