Page 301 - Making PIC Microcontroller Instruments and Controllers

A
PROJECT 303

will be collected. The collector ceases to collect fsther energy for a number of reasons
that do rct concern us here. Our interest is focused on how io rcmove energy liom the
collector so we can maximize the amount of energy that can be collected, We can do this
by adding a smali cooling fan, like one recycled from an old computer cabinet, to move
the air through the collector We could also add a couple of fabric check valves at the
inlet and outlet to keep the air ftom blowing backwards through the collector when the
fan is off, if necessary. We wil use 135'F always (adj) as the ma\ permitted tempera-
ture in our experiment to reflect residential heating conditions. We will tum the tan on
if the internal temperature reaches 135T but this temperatue can be made adjustable by
comparing it to the r€ading or one of the orboard potentiometers (he set poino.
We will collect the data once every minute to get an accurate prolile of how much
energy the collector caplures during the day. Let's assign I byte to each digit we have
to collect, even though we are aware that the data could be packed much more tightly.
The temperature willbe read in degrees Fahrenheit so we will need 3 bytes for the tem-
perature. The infomation we collect consists of the lbllowing data points:

l. Date and time of day, 12 bytes (YYMMDDHHMMSS)
2. Temperatwe inside the cabinet, 3 bytes (TTT)
3. Whether rhe fan is on or off, I byte ( F : 0 or 1)

These 16 bytes have to be collected 60 times an hour all day and all night. (We are
collecting nighttime data to allow Dr. Sun to estimate the heatirg ne€ds in the area during
evenings.) We have to collect an average of 23,040 (16 X 60 X 24) bytes every day.
To make things move along and to allow for overhead and so on,lecs say thatweneed
space for 25K ofdata every day in round numbers, which would be 9125K of data in
a year. Nor a large amount ofdata considering the capability ofeven the smallest com-
puters on the market, and within reach of storage in an MC U-based engine without any
external storage if we could add a modest amount of memory to the MCU. We could
ship the data to Dr. Sun at the Peking all these also need to be changed to keep with
Beijjng elsewbere Polytechnic University in Beijing on a CD-ROM or over the Intemel,
if the collection point has Web access. (Vr'e should contact Dr Sun to inform him that
the project could very easily be modified to collect the data every 30 seconds, or even
more often, at no additional cost.)
Our preceding calculations have indicated that the problem is completely within
our reach and so we can proceed wilh t}re fabrication of our collector and the design
of the hardware and software we will need to get the job done. The drawings lbr
the collector are on the Web site that s ppofts this text, so we will not go inlo lab
ication details here. Our interest is in the electronics and the software, but you are
encouraged lo make up a rudimentary collector to see how the project comes
together. A few sheets of cardboard, a bit of sheet Styrofoam, a few scraps ofwood,
and some plastic sheeting will make a surprisingly effective collector that you can
experiment with.
For the complete project, we need the items shown in Table 22.1:
Study the wiring diagram in Figure 22.3 to get familiar with how the various com-
ponents are wir€d to the LAB-XI befor€ starlirg on the fabrication.