Page 188 - Making PIC Microcontroller Instruments and Controllers

|NSTBUiIEIN ABACKCROUI{D
tA4 THE UI{TVERSAL DISCUSSION

the computer is the selector switch! (Note that in the newer VOMS, some auto
ranging capabilities are implemented fbr selecting the range used by thlr meter' The
output, loo.ls ranged so it can fit in the limited number of characters in the display
To us. this means some oflhe decision naking we might havc undetaken has been
rclegated to the intelligence buill into the machine ) The flexibilily oforr. hrtr&m?rrs
is rcoted in the abilily Io reprogram lhe instrumenlwilh a few keysrokes whenever
neealed. In ofder to be able to use lhis flexibility, we must design the hardware for
our instmments iD a lvay thar will lend itselfto softwarc nodification wjth relaiively
minimal cffort in arelalively short tine. we hare to think about what thc insnxmenv
controller will/can do as wc design it so it will pedorm its intended iunclions with
keep in mind that the instrument will do only what wc design
some elegancc.Always
ir lo do. you must @ mit this unrcp! toYur broiir' It is v€ry important
3. The device must have a wi\y ro ot\tPl|l itlforndlion in a useful format The lbrmat
CRT display On
can be anythirg liom a simple switch closurc lo a comprehensivc
the VOM, a few digits suffice to givc us ihe informatjon we need. On instrumenls
the addilion ofa two line display canprovide a con
based on PIC miorccontrollers,
sialemble amount of infonnation. The many output port lines can be used to tum LEDS
on and oli and to provide other on/off signals. A serial port can be used to send and
feceive information from a computer Audio signals can also be added. Versatility
will be our slrong suit.
4, The infornalion/output desired should be able to be.rldrilirzl for a while sowe can
collcct it. Some ol the newer VOMS have a storage function thal lcts you freezc the
display at selected pcak values or al sclected tines. Our instrunents will be able to
do that and se the information to a computer at selected intervals for storage in that
computer 1o facilitale fulure analysis. Thcy will be able to make decisio s in real tine
when we are not therc. and take correcdvc actions, or summon human intervention.
The capabilities we can incorporate into our instruments are limited only by our
imagination. wc are the designcrs.

A B asic Temperature-Controlling

Device

Next, we will discuss lhis in the conlext ofa simple temperaturc-co rolling device. Late!
we will actually build this device.
What are the basic propcrties and componenis ofan instrument that can be described
as auniversal all-purpose single'point conlroller? Basically. the following functions are
called lbr:

I Sense condition
! Set a point ofconirol
! Compare &e pteceding two ilnctions
! Output a sigsl