Explanation of map function is wrong

[blnkjns]

I found dozens of Youtube tutorials and they all follow your guide on Map ( ), but the function behaves not as it should behave. I know the internals are perfectly logical from a programmers perspective with its head into integer divides, but they are NOT from an engineers perspective.

map() - Arduino Reference

The most demo-ed example is to map a potentiometer to a LED PWM value. 99% of tutorials does this:

output=map(input,0,1023,0,255);

But because of integer divide behaviour, this does not lead to the desired result. Value 0-4 turn into 0, where only 1023 becomes 255. Another example:

output=map(input,0,1023,0,100);

This example will NEVER give 100 as outcome!
I found by testing all sort of combinations, we ALWAYS need to add 1 to both high ends of the ranges, or subtract 1 if the range is in reverse order.
so the LED PWM example done right is (with perfect 1 outcome on every 4 input values evenly distributed):

output=map(input,0,1024,0,256);

and if you want to remap it to say 100 to -100, you should do

output=map(input,0,1024,100,-101);

Can someone please fix the documentation on this?

[anon73444976]

blnkjns:
The most demo-ed example is to map a potentiometer to a LED PWM value. 99% of tutorials does this:

output=map(input,0,1023,0,255);

output = input / 4;

There, fixed.

[dlloyd]

I wouldn't constrain() your research to the use of map(), the Arduino reference would be the first pace I'd check.