Barometric Pressure Double Feature
power source into the 2.1 coax. Refer
to the carrier instruction manual for
To test the interface to the
SCP1000, load and run Program 1.
This will display the pressure reading
in Pascal units on debug terminal.
I have also included a second
program called Program2.txt that will
display the temperature.
The program called bargraph1.txt
is the main plotting program. While
the program is a bit lengthy to present
here, I will describe a few of the
details that you may want to change in
■ FIGURE 9
■ FIGURE 8
the current hour index at the time of
At the very beginning of the
program is a statement where I assign
a constant called offset. This is a
value that will allow you to change the
absolute pressure value to the station
pressure. This value is added to the
absolute value. You should change
this value so that your pressure gauge
reads the same as your local forecast.
The display has a vertical line near
the center of the display shown in
Figure 8. The plot to the left of this line
represents the last 50 hours of
pressure readings. The plot to the right
of this line is a 12 hour projection. On
the upper righthand side of the display
is the current barometric pressure and
inside temperature. On the lower
righthand side is the 12 hour forecast
my R/C helicopter and found that in
order to get the high resolution
required, you need to read the
SCP1000 about once every 1.8
seconds. This is too long for this type
of application, however, I have read
where others have taken two
SCP1000s and alternated the readings
in order to double the sample rate.
This also gives you some redundancy
in case of a failure.
The first portion of the plot is the
last 48 hour history. This data is saved
into the first 96 EEPROM locations.
When you program the DiosPro, the
data statements at the beginning of
the program initialize these locations.
You can comment these statements
out if you want to experiment with
your exiting data so that they won’t
Once you have programmed the
DiosPro and have verified that it is
working properly, you can configure
the program port to connect to the
onboard hardware UART by setting
the DB9 jumpers. The small bit of
code following the loop label tests for
a character value of 65 at each pass.
If this value is received, the complete
20 day history will be sent out the
UART at 9600 baud. The data is
dumped with the low order byte first,
then the high order byte. Each byte
pair represents one hour of data with
a total of 460 hours. The first pair is
How Well Does it Work?
I have been using this pressure
sensor for the last couple months and
it works pretty well. It has accurately
predicted the weather for most
changes in my area. For instance,
while I was writing the display indicated that a change in the weather was
going to occur in the next 12 hours.
My grass was getting tall and if it were
to rain I would have to wait another
week to cut it, so I stopped everything
and took out my mower. Sure enough,
about 13 hours later it started to rain.
I prefer the SCP1000 pressure
sensor over the 1-Wire sensors that I
have used, as it seems to give a more
reliable reading and does not require
14V to operate.
Now it’s time to take a totally
different approach and build a talking
barometer. I wanted to keep things
as simple as possible, so we will take
the modular approach on this project.
I will take various boards that are
readily available, both assembled and
in kit form, and create the talking
barometer shown in Figure 9.
All that is needed to
make this display wireless is to add a Zigbee
unit. I will look into
doing just that when
I build the wireless
station next month.
I had experimented
with the SCP1000 for
use in other projects like
If you can solder, then you can
build this project. Even if you can’t,
you can probably get someone to
assemble the various modules. Let’s
■ FIGURE 10
July 2007 43