Page 192 - Making PIC Microcontroller Instruments and Controllers

PULISES! PROGnA iIABIE TACHOMETEF
taA COUNTIIIG A

i:t!!!i-iltfgif:: A programmable tachometer.

out at times. When using a LAB-XI, we know we have a working platiorm to develop
the software without having to worry about hardware problems that we might have cre
ateal lor o rselves. After we have the tachometer software workng. we can use the LAB-
Xl to create pulses generated at known frequencies to check the accuracy of the
instrument we created,
dispiays has to do with leamjng
The displaying of the counts on 4 seven-segment
how to use these commoniy used and inexpensive displays.It is, ofcourse' much easier
to display the information on the 2 x 20 LCD on the LAB Xl, but in this exercise we
will be using th.- LAB-XI only as our initial software platlbml. If you prefer the proj
ect can easily be modified to rul1 on the LAB -X 1, but then you will miss out on the expe-
rience oflearning how to use the seven segment displays. In any case' the PIC we use
will be lhe l6F8??A. (This PIC will be employed for all the projects in this book' and
the LAB X1 will be used to suppoft all the projects as needed )
The facl that we ar€ using only four displays is because the integer math provided in
the compi ler can handle only 16 bit math (65535 max), which limits us tofourdisplays
if we want to go to a 9 in the Left-most display. It also simplifies our problem at this stage
anal will demonstrate that refreshing lbur di splays takes us to the ma,\imum that the PIC
can confol (at 4 MIIZ) without having to use assembly language programmj ng lt is also
a compronr.ise that has to do with the fact that four digits can be handled easily with
one dnd a half pofts (12lines.|.
We will be using a small dc motor with a 2o-slots-per revolution encoder (available
on it as our signal gencrator (see Figure I 5 -2), but
from my Website encodergeek.com)
before we do that we need to undertake some general discussion about counting pulses
and what the problems related with low and high "counts/time penod" are. If you have
some other device tha! can generate pulses, you can use it if you like.