Math

10gigbill · 2020-11-05 16:34

I want to type in a number zero to 6000 and multiply it by .682 and make the result
an integer zero to 4095 to send to a 12 bit D/A. I can't get the math to work???
thank you for your support...

{{          test program
}}
Con                           
_Clkmode = Xtal1 + pll16x       
_Xinfreq = 5_000_000
multi = 0.682
 
Var
   LONG outval        'end count
   long inval        'start count
   LONG oneval
   
Obj
  pst:          "Parallax Serial Terminal"    
 
Pub   main 
     pst.start(115_200)     'check the baud rate
     pst.str(string("hello",$0D))
   
   repeat
           pst.rxflush
           pst.str(string("Gimmie a number --  ",$0D))
           inval:=pst.Decin 
           pst.str(string("got it... your answer is...",$0D))
           outval := inval * multi
           pst.Dec (outval)

whicker · 2020-11-05 16:59

Spin only natively uses integers. As in whole numbers.

It would help if you took one step back from how you calculated .682, which can be expressed as a numerator / denominator pair.

Multiply first, then divide.

outval := inval * 4095 / 6000

10gigbill · 2020-11-05 17:19

Wow! that was E Z... that works fine... I think I missed class that day....

Thanks Whicker...

Bill.

Ltech · 2020-11-05 17:27

Or multiply by 1000 you "multi = 0.682" => 682 so you avoid the fractions

And result "outval := (inval * multi) /1000

Duane Degn · 2020-11-05 17:40

If you want to display decimal values you can use the method "DecPoint" as shown below. If you want three digits after the decimal use 1000 for the value of "denominator".

This assumes "value" is scaled by the value of "denominator".


PUB DecPoint(value, denominator)                                             
  
  if value < 0
    Pst.Char("-")
    -value
      
  if value => denominator
    result := value / denominator
    Pst.Dec(result)
    value //= denominator     
  else    
    Pst.Char("0")
  Pst.Char(".")  
  repeat while denominator > 1
    denominator /= 10
    if value => denominator
      result := value / denominator
      Pst.Dec(result)
      value //= denominator
    else
      Pst.Char("0")

Math

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