newbie wants help with integer division

harry_s

Hi all

I am trying to experiment with PID...I am using an analog input of temperature spaning from 0 to 50C and I am using an ADO0831 with input span 0-5VOLTS.

I am calculating the temperature by

t= tempSpan * adcBits/255

I wanted to use the trick with the tenths of temperature that the stamp in class- industrial control uses but I get wrong results since I fail the result of the mutiplication is bigger than 64k...

how do I resolve this problem?

Can you please also recommend some source of information & tricks on how to do floating point calculations on basic stamp?

Thank you

Bean

I think the problem is that your input cannot be to the tenth of a degree (that would require an input value from 0 to 500).
But you could get the temperature in 0.2 degree increments.

Make tempSpan = 250 ' 50 / 0.2

t = (tempSpan * adcBits) / 255

tWhole = t / 5
tFrac = t // 5

Bean.

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Mike Green

If you're interested, there's a discussion of multiple precision arithmetic with the Stamp including examples here under math: www.emesystems.com

Tracy Allen

Harry,

You can probably use the */ operator. On your calculator find, multiiplier = tempSpan * 10. Then use,

t = multiplier */ ADCbits

That will not have the overflow limiitation and the result will come out directly in tenths.

Edited: I had included a divide by 256 in the calculation of the multiplier. That is implied in the */ operator.

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Post Edited (Tracy Allen) : 7/31/2007 9:18:16 PM GMT

harry_s

Thank you all for your answers !!!