VIDEO VBOX LITE MANUAL
Page | 70
22 December 2009
4: Calculating the gradient of the line
The gradient of a line is the change in Y divided by the change in X which gives:
m = dY/dX
dY = 100 – 0 = 100
dX = 5 – 0.5 = 4.5
Therefore the gradient of the line is:
dY/dX = (100 - 0)/(5 – 0.5)
= 22.22
5: Substituting values to find the offset
To find the offset value we simply substitute the known values back into our equation as follows:
Taking the values when the pedal is not pressed.
Y = percent = 0, X = Voltage = 0.5 V
Y = mX + c
Therefore
0 = (22.22 * 0.5) + c
0 = 11.11 + c
Taking 11.11 from both sides of the equation gives us:
C = -11.11
6: The full equation for the line
Substituting these values back into the equation again gives us the full equation of the line which passes through our
two points.
Y = 22.22X – 11.11
7: Checking the equation
We can double check our equation is correct by calculating a percentage value for a known voltage output.
We know that:
Using the equation we have just derived produces the following results:
Y = 22.22X – 11.11
Y = (22.22 *
0.5
) – 11.11 =
0%
This is correct, as 0.5 volts is equal to a 0% pedal press.
Y = (22.22 *
5.0
) – 11.11 =
99.99%
This is also correct as we know that 5 volts = 100% pedal press.
8: Plotting the full line
The graph below illustrates the calculated scale and offset
values.
Voltage (x)
Percent Pedal Press (y)
0.5
0
5
100
