shorted (by pushing the button) or
not shorted (by removing the
shorting block). A low dropout
voltage regulator and power indicator
LED complete the circuit.
Possible Modifications
One modification to make is to
replace the 91K ohm resistor with a
resistor of 10M ohms. This increases
the sensitivity of the pressure sensor
so it can measure changes
in the daily air pressure. I’m
still investigating this, but
it’s possible the circuit will
be better with a 4.7M ohm
resistor. The reason I say
this is that it appears my
quadcopter can lift the
weather station high
enough (400 feet AGL) to
drive the pressure sensor to
its minimum pressure.
A second modification
is to solder the 24LC256 to
a separate PCB and plug it
into the weather station’s
PCB. This modification
allows a user to leave the
weather station in some
location and then switch
out and swap the memory
chips after the PICAXE has
filled them with data.
A final modification
(which I have not
attempted yet) is to plug an
XBee radio into the
programming port. This
would allow the recording
weather station to transmit
data from a remote
location. A second XBee
would be needed along
with a way to see the data
coming over the XBee link.
Using the
Recording
Weather Station
After completing the
weather station, you need
to set up the pressure
sensor and calibrate it. The 500 ohm
trimmer connected to its + and –
pins of the MPS-3138 is used to
balance both sides of the
Wheatstone bridge.
So, write a short program to
digitize the output from the op-amp
and debug the results at one second
intervals. Then, adjust the trimmer
until the voltage is maximized. I
I have attempted to
calibrate the pressure sensor
using a 35 mL syringe to
some success, but am not
completely happy with the
results. Do not calibrate the
pressure sensor using air
pressure data from your
local airport. That air
pressure is converted to sea
level air pressure so aircraft
can set their barometric
altimeters.
Some Initial
Experimental
Results
It’s not near space
season in Idaho yet as I
write this article. In fact, I’ve
been shoveling 24 inches of
snow rather than working
on near space. Therefore,
the results I’ve created so
far involve driving the
weather station to school,
letting the weather station
record conditions at the
house over 24 hours, and
lofting it with my
quadcopter. Following are
some of the results I’d like
to share with you.
Weather Station
for January 1-2
While shoveling snow,
56 June 2017
Pressure.
Temperature.
1-2 January 2017
1-2 January 2017
1-2 January 2017
Relative Humidity.