Building Robots With Lego Mindstorms

228 Chapter 12 • Doing the Math

If you are familiar with college math, you will recognize in m the slope of

the straight line that connects two points. Now our equation becomes:

Y = m x X – m x X

a

+ Y

a

As s, X

a

and Y

a

are all known constants, we compute a new term b as:

b = Y

a

– m x X

a

so our final equation becomes:

Y = m x X + b

This is the standard equation of a straight line in the Cartesian plane. Looking

back to our previous example, you can now compute m and b for your tempera-

ture sensor:

m = (50 – 0) / (450 – 200) = 0.2

b = 0 – 0.2 x 200 = –40

Y = 0.2 x X – 40

You can confirm your previous result:

Y = 0.2 x 315 – 40 = 23

Implementing this equation inside ...