Page 304 - Making PIC Microcontroller Instruments and Controllers

306 LOGGIIIG DAIA FBOIII A SOIAB COLTECTOR

Software

Nole The solwarc listinls are v,ritten as il the controLler \')as a LAB Xi boa
so that a new boanl does not haw to be created to execute the requirements ofthe
eryeriment- A much more wn!1tile slstem could be created if a new board was
desi!ne(]. Since the major ptoblem wth the LAB xl is the fact that therc a,e three
pots atreadJ dttached to the anaLog input lines, the circuit layout for this e.rperi'
ment must refect this.
The devices we will be using are to be attached as fbllows:

The temperatwe will be read from PORTA.5.
The clock uses the Nru6355 chip and is located as shown on the LAB_Xl schematic
at U6.
A32.786-KHz c.ystal mustbe added to the board at J5 to support the clock.

The fan switch will be at PORTD.3.
The inteface fo the computer will be the DBg connector on the board
The LCD display addresses will be the standard LCD adalresses for the bodrd.

The software for the solar collector has to peform the following functions:

Provide a clock function (with the hardware addition)
Read the temperature sensor

Make minor decisions / Control the lan
Send the data to the computer periodically
Reco\er frcm po$ er oulage. rutomalicalll

The hardware needed to support these functions is shown on the wirjng diagran in
Figue 22.2, with all the pins that will be used identified.
If there is no battery backup, the clock must have an arbitrary starting time so tlte
recovery from apoweroutage canbe effected based on the datacollected during the
previous and following day. When the data is analyzed, any reset/discontinuity of
the clock will indicate a power outage and the rcadings will have to be adjusted fbr
time ofday based on extrapolation from the daily cycles. Dr' Sun has indicated that
these functions are to be performed when the data is finally analyzed by his group
in Beijing.
Let's write the software as subroutines, one for each function Each of the sub
routines needs to have some prcliminary work done up front during the setup oflhe
program, and this is listed separateiy before each subroutine.
First,let's setup the LCD as we always do. Then, we can call the code oul as a sub-
routine in the program where we need it. See Progmm 22 1.