powered data logger with the SHT11 sensor module. I
attached the batteries so I could put it in my car overnight
where I knew the temperature and humidity changes
would be more dramatic than inside my home.
Figure 7 shows communications with the data logger
via my Android phone. Sadly, iPhone users are not allowed
access to serial Bluetooth modules, so this won’t work for
you (I’m exploring options for a future column). You’ll
notice the last command displayed, THNOW, shows the
time, temperature, and humidity. When logging is activated,
a string like this is written to the target file every minute
(the logger lets you set the number of samples to read).
In Figure 8, you can see that I opened the file using
OpenOffice Calc, and then created a graph of the
temperature and humidity measured in my car while I was
sleeping. What I find particularly interesting is that the
humidity jumps near sunrise, even though the temperature
is still falling slightly.
Okay, then. Whether you’re building a
greenhouse controller as I hope to do, or just
want to know what’s going on in your
environment, the SHT11 module will let you do it.
Have fun with this data logger. Since creating my
parser, I have leaned toward interactive versus
menu-based programs, and I’m having a great time. Give it
a try. I think you will enjoy it too!
Until next time, keep spinning and winning with the
December 2015 19
Propeller Activity Board Parallax #32910
SHT11 Sensor Module Parallax #28018
Li-Ion Power Pack Parallax #28989 (optional)
RN- 42 Xbee Module SparkFun #WRL-11601 (optional)
■ FIGURE 8. Graph logger values.