only one analog channel coming into MakerPlot.
What’s important to note are the text boxes to the
right of the color squares. These are what we need to
change in order to scale the analog data to make it
conform to the actual voltage level that the
micro sees at the A0 pin. The first text box (the
one that has a 1 in it now) is the multiplier
adjustment value. Right now, it’s set to 1
meaning that whatever analog value comes into
MakerPlot on channel 0, that’s what will be
plotted, i.e., the analog value times one (x1).
This holds true since our analog value range is 0
to 1023 at the moment — which is what we’re
seeing on the plot.
Doing the Math
The value in the first text box needs to be
changed to a decimal fraction to represent the
true potentiometer voltage value. Here’s the
equation to determine this fractional value:
X = 5.00 volts / 1024 steps
= 0.00488 volts / step
This means that each step of the A2D
converter is worth 0.00488 volts. So, click on
the first text box and key in 0.00488; make sure
to push the Enter key (Figure 12). Now look at
the plot; it’s nearly at the bottom of the plot
area. This is to be expected, since now we need
56 December 2013
Figure 16. Add negative bias.
Figure 14. Label Y axis.
Figure 15. Add positive bias.