Page 277 - Making PIC Microcontroller Instruments and Controllers

27G atl aFtlFlclAl HORIZOII: A TADLE SURFAGE tH/tT SIaYS IEVEI

and not very precise. cadboard construction. This can be taken care mathematically
in the software with a lookup table or an equation depending on how well the mecha-
nism responds to the tilt of the base. Since the correcting mechanism designed for each
table setup will be different, the implementation of this will be left up to each individ-
ual consfuctor, but we will cover the general principals. If we put the senson at the table
surface, none of this matte because we ar€ sensing the actual tilt of the table and this
is beyond lhe effe(t of lhe Inkagec. and .o on.
I think it is really important for you to actually build a table. It does not have to be
anything fancy, aIId you will discover all kinds ofthings about controlling the table that
just will not occur to you if you don't have a table to play with. Though the concept is
losing currency among our educato$, nothing beats working with your hands and your
mind. They reinforce one another. I built everything in tbis book many times over!
Figure 19.3 shows a picture of a table I built out of cardboard. The table components
were cut out from an old cardboard box with a box knife and a pajr of scissors, and then
gtued together with hot glue. Since our interest is in the control of the tablo as opposed
to the table itself, a simple cardboard model lets us do what we want at minimal cost
and with minimal effort. Fort|lnately, the slight sloppiness and iDaccumcies in the cor-
struction of the table lend ihemselves to software coffections. My table is shown in
Fisues 19.3 and 19.4.

ffiiumffilffi Picture of simple horizontal
table and lhe gravity sensor; the basic table
mechanism can be made outofcardboard.