PWM/Temp setting help with math? or code.

[wdmagic]

that looks pretty good henrik, no I didn't say "20 or 25%, you claim both...." I said it needs to be 25% and existing is 20%, but thats ok, yes it needs to be 25%
I forgot what does "*/" do again?


and arrati, that code is basically what I had started with but didnt work because the end result max would have been 100 and I needed it to be 255, see henrik's code, he did 25% of 255 which is 64, I wasnt thinking when i made my code 55 and then I ended up getting a 20% minimum. numbers are important a decimal in the wrong place, 1 didgit off can ruin code. but thanks, everyones Ideas help somewhere even if its not today.

[HenrikOlsson]

Hi,

The */ operator multiplies the two values you give it and the discards the least significant byte of the result. It's the same thing as first multiplying then dividing by 256. The good thing is that intermeditate result can be large within limits and you won't overflow like you would if you did the same thing "manually".

Put another way, the */ operator multiplies by units of 1/256. So:
100 */ 64 = 25
100 */ 128 = 50
100 */ 256 = 100
100 */ 384 = 150
100 */ 512 = 200
and so on.

Lets say you have a value of 123 and want to multiply it by say 3.477 (the correct answer is 427.67). To find the number to use with the */ operator all you need to do is 3.477*256=890. 123*/890 will return 427.

/Henrik.

[LinkMTech]

Sorry if I'm hijacking here but wanted thank you Henrik for the cool tip!
I've been experimenting with a 2000dps gyroscope that outputs a max of 32757 counts.
Then with the resolution at 0.07dps, I had to use LONG's to make (32757*0.07=2292.99dps) work.

INTxg   VAR   WORD
Xg      VAR   LONG

INTxg = (Xg*7)/100   ' Xg max value =32757


   *** changed to ***


INTxg   VAR   WORD
Xg      VAR   WORD

INTxg = Xg*/18   ' 0.07*256=17.92 for (32757*18)/256=2303, rounding up only 0.43% error at max

I didn't know if it would work without LONGs but it did, and trimmed 1356 Words in my program!