Dear piclist guru's,

I have to do an automatic calibration procedure for a transducer.
This will be read by pic internal 10bit AD converter.
Assuming the whole AD range is 1024 and the transducer characteristic
is linear one, I need to read 2 points to determine the correct slope.
Zero will be between 300...400 and full scale between 950 and 1023 and
depends by transducer characteristics and biasing. No external scaling
device like operational amplifiers will be used.
I need interchangeability between various transducers which will match
condition above.
I'm new in pic maths so I was thinking to the following procedure
exemplified with one transducer values, all numbers are in decimal
representation:

1. measuring zero calibration value
   cal_zero = 376
   at cal_zero, displayed value must be tmin=0
2. measuring full scale calibration value
   full_scale = 978
   at full_scale, displayed value must be tmax=98.9
3. determine real scale
   real_scale = full_scale - cal_zero
   real_scale = 602
4. compute slope
   slope = real_scale/tmax
   slope = 602/98.9 = 6.08
   I want to use only fixed point unsigned math routine so I need some
trick
for this division:
   integer_slope = 10*602/989 = 6, remainder_lo=86
I will use 16bit division routine and check:
 if remainder_hi = 0 then
  100*remainder_lo/tmax = fraction_slope_lo
  fraction_slope_hi = 0
  100*86/989 = 8; new_remainder is not important
 elsif remainder_hi > 0 then
  10*remainder_hi:lo/tmax = fraction_slope_hi:lo
 end if
At this moment I know 100*slope = 608
5. determine real displayed value
   real_value = 100*(measured_value-376)/100*slope
   real_value_t_max = 100*602/608 = 99.1  (full scale display)
   real_value_t_min = 100*1/608 = 0.16 ( first display greater than 0 )
  This division will be computed in same way like above one.
   I will have an error of about 0.2% at full scale which is enough.

 Now the question: could be done this computation into an easy way ?
Here I must use 16b substraction, 16b multiply, 16b division and some
conversion from hex to decimal.

 Thank's for your existence,
Vasile

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