How to adjust values to a new range

[HenrikOlsson]

This has been covered many many times on the forum so why not one more time...

Basically we want multiply the ADC value by 135/1023=0.132 so in comes the */ operator.... 0.132*256=34 (rounded up).

1023*34/256=135
512*34/256=68
128*34/256=17

When the value you want to multiply by is <1 you can get more precision with the ** operator (same thing but inherent division by 65536). In this case it doesn't matter though because the output value range is so small.

Do note that there's no expensive division going on here, all it does is discard the bottom 8 bits (in the case of */) of the multiplication.

/Henrik.

[Ioannis]

If for any reason the input may have a value over 1023 then there would be a problem with the simple equation. But since the that value comes from a specific 10 bits ADC module it defines the upper limit of 1023.

If you want to use it in other cases, a MIN/MAX would be needed.

In any case Henrik's solution is neat and fast.

Ioannis

[Demon]

This has been covered many many times on the forum so why not one more time...

You've explained it, using my own problem as example, and I still don't completely understand it. My eyes sort of gloss over when I've read these explanations on the forum. And it's not getting better as I get older.


I really do appreciate you holding my hand while you pound this into my skull.

[HenrikOlsson]

Allright...

[1] I believe you're with me for the 135/1023=0.132 part, right?

[2] IF the description for the */ operator WOULD have said "....resulting in an automatic division by 1000" then I think you'd see that the solultion WOULD be OutputValue = 100 + (InputValue */ 132), because 0.132*1000=132, correct?

[3] But since the */ operator "....resulting in an automatic division by 256" we must multiply 0.132 by 256 instead of 1000. Hence the value 34.

Makes sense? If not, which step?

[Demon]

I follow. I just could not have thought of this by myself.

[Ioannis]

Or maybe use a formula

X=135*256/1023

where X is the number you wan to use in the */

135 is the max scale value

1023 is the max ADC value

Ioannis

[amgen]

error posting

[Demon]

not to beat this up too much........

A horse is never too dead on the web.

... if you only need 135 output values, and you want to scale pot for 0 to 100%..... just use the top 8 bit from a/d and this trend line function that excel gave.

I can't believe I was playing with excel all that time and never thought of using the chart feature.

[Demon]

My ADC is only 10 bits, not 16.

So I just divide 10bits by 4 to reduce from 1023 down to 255, then slap it through your formula.

I haven't done any math yet (just thinking, while I work on my encoder logic), but this probably equates to what Ioannis is suggesting.