I forget

Comments

• Tracy Allen Posts: 6,667

  2008-01-05 22:52 edited 2008-01-05 22:52

  Hi Sid, Happy new year!
  
  You can use ** instead of */ to improve the resolution, because the implied denominator is one part in 65536 instead of one part in 256. Say you want to multiply a variable x times 3.141593.
  
  Using */ you would use y = x */ 804, because 804/256 is the closest approximation with that denominator of 2^8. Suppose x=10000. Then
  y = x */ 804
  will equal 31406, which is 10 less than the most correct answer, which is 31416. You could use
  y = x */ 805.
  which equals 31445, 29 units too high.
  
  With ** instead, you would use, y = (x * 3) + (x ** 9280). That is because 9280/65536 is the closest approximation to 0.141593 with the 2^16 denominator. Again with x=10000,
  y = (x * 3) + (x ** 9280)
  comes out to 31416, as desired. It will be at most one unit off of the correct answer due to roundoff.
  
  Sid, does that answer your question?
  
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  Tracy Allen
  www.emesystems.com
• Newzed Posts: 2,503

  2008-01-05 23:00 edited 2008-01-05 23:00

  Thanks a lot, Tracy.· Could you simplify that a bit for me?· I have my ADC reading the wiper of a pot across 5V, and I get 2317.· I want to modify the raw reading of 2317 so that my Stamp displays 497.· How would I write that - I··think I understand but I want to be sure.
  
  Sid
  
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  Yesterday is history, tomorrow is a mystery, and today is a gift.
  
  That is why they call it the present.
  
  Don't have VGA?
  Newzed@aol.com
  ·
• Newzed Posts: 2,503

  2008-01-05 23:13 edited 2008-01-05 23:13

  Never mind, Tracy - I've got it.· Thanks a million.
  
  Sid
  
  ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
  Yesterday is history, tomorrow is a mystery, and today is a gift.
  
  That is why they call it the present.
  
  Don't have VGA?
  Newzed@aol.com
  ·
• Tracy Allen Posts: 6,667

  2008-01-06 21:01 edited 2008-01-06 21:01

  Yes,
  

  y = x ** 14058
  

  
  
  will give y=497 when x = 2317.
  Is that what you have?
  Note that it could be better, as that calculation is losing significant figures. You could also do
  

  y = x ** 28116 * 5
  DEBUG DEC y/10, ".", DEC1 y
  

  
  
  and that would print out 497.0 and progress by units of 0.5 as x changes.
  
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  Tracy Allen
  www.emesystems.com
• Newzed Posts: 2,503

  2008-01-06 21:29 edited 2008-01-06 21:29

  Tracy, that works even better!· Thanks again.
  
  Sid
  
  ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
  Yesterday is history, tomorrow is a mystery, and today is a gift.
  
  That is why they call it the present.
  
  Don't have VGA?
  Newzed@aol.com
  ·