Floating point - please enlighten me!

[cncmachineguy]

Gee, and you question SO looked like you needed to multiply a whole number by .2235 and the .2235 was where the trouble is. If you need .00044*.2235, thats a different problem. You are correct, your question was simplified.Where are you getting numbers like .00044 in your pic? how is that generated?

[mark30504]

Gee, and you question SO looked like you needed to multiply a whole number by .2235 and the .2235 was where the trouble is. If you need .00044*.2235, thats a different problem. You are correct, your question was simplified.Where are you getting numbers like .00044 in your pic? how is that generated?

Hello

Thanks

I am just trying to understand the work around format in PIC to work with floating point values, the systems I normally program have floating point at part of there normal stucture.

I though from the orignal post that all you needed to do is use fractions in your formula and it would work but it does not seem to be so.

For example If I needed to multiply some varriable by .234 or any decimal value to get an answer, how would this be done?

In my case I am takeing a analog voltage and turning in into a tempature that is displayed on a screen.

The temperature result does not need to be floating point

But if I can not use floating point numbers to scale correctly the value could be off by 5+- degrees pretty quickly

The true formula is

result=adc10((adc10*.00034)+.2235) 'where adc10 in the pic 10 analog register

To be within 1% of the true tempature

Thanks

[cncmachineguy]

The true formula is

result=adc10((adc10*.00034)+.2235) 'where adc10 in the pic 10 analog register

To be within 1% of the true tempature

Thanks

so plugging in extremes:
adc10=1 gives us
result=1((1*.00034)+.2235)=1(.00034+.2235)=1(.2238 4)=.22384
adc10=1023 gives us
result=1023((1023*.00034)+.2235)=1023(.34782+.2235 )=1023(.57132)=584.46036

Is this correct? Seems like quite a lot of work to scale an answer. what temps do the extremes represent?

[mackrackit]

Back up to post #8

The constants
.00034
.2235
Would be changed to
34
223
In your formula.
Then at the end you would divide by a power of ten.
If all of this fits into the variable type used
BYTE
WORD
LONG
then the result will be truncated to an integer.
Truncating to an integer is what you wanted...