Page 191 - Making PIC Microcontroller Instruments and Controllers

COUNTING PULSES:

A PROGRAMMABLE TACHOMETER

Proiect I

In thj s first project, we build a programmable tachometer that can delect belween I and
9999 pulses a second (or another time period) and display the results on 4 seven
segment LED numeric displays. Thesepulses can be counted in two ways.Ifwe know
we are getting a fixed duty cycle square wave, we can measure lhe total length of a pulse
and detemine the frequency of the signal from that. If the pulses are not coming at a
regular rate, we can actually count the pulses over time and determine the rate ihat way-
We can write the software for both techniques so we can see the difference. At the end
of the project, we will take the source of the pulses into consideration and discuss how
to modify the software to display an actual rpm (revolutions per rlinute).
when working with miooprccessors, much of the infonnation we deal with is read
and processed as pulses, counts, frequencies, and the like because miooprccessors are
digitaldevices, and are usually not designed for handljng analog vdlues. So il becomes
impotant that you be comfortable with gathering, processing, and displaying infbrma-
tion of a digital nature, and this project focuses on that aspect of our knowledge and
understanding regading microprocessors. Once you are comforlable with the design and
consfuction of this tachometer, you will be able to handle all other frcquency input proj-
ects with confidence.
We will use the LAB-XI board as a helper instrument as we go along. Fhst, we will
make the software work on the LAB-XI (when we can) and once we know we can rcad,
count, and display the inputs the way we want, we will move on to the fabrication of
LED based tacbometer showr in Figure 15.1.
the seven-segmert
In this project, the LAB X1 will be particularly helpful because seven-segmenl dis
plays require a lot or wiring (that can go \\'ong) and it can be dillicult to get things sorted

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