Photo 4 shows a somewhat different program
( hour_bmp085_GLCD_graph_baro.ino) with a single
graph updated every minute. The whole thing represents
Photo 5 shows the same Arduino-GLCD combination,
this time with a different program ( general_graph.ino). This
one has the barometric code stripped out, and simply
graphs the voltage on pin A4. The same hardware setup
works here; just leave out the barometric sensor.
The entire graph spans eight hours. It is tracking the
voltage on two 18650 lithium rechargeable cells in
parallel, with a 7. 5 ohm resistor load. I was curious to see
how these cells would hold up since they were salvaged
from an old laptop battery.
This illustrates how just about any slow-moving signal
(such as temperature) can be graphed with this setup.
Voltages higher than 5V can be scaled down with a
voltage divider. The time between graph samples can be
adjusted easily in the program (currently, delay(240000)
equals 240 seconds, or four minutes).
Counts per unit time from a Geiger tube could easily
be mapped into the graph range and plotted. There is a
chance that a sensor can pick up solar storms. A
Honeywell HMC5883L has a two milligauss sensitivity; a
plot of that might be interesting.
The wiring chart is in Figure 1.
A few pitfalls: Be sure to follow the instructions when
installing the Arduino libraries. Just copy the zip file into
the Arduino directory, then open the integrated
development environment (IDE) and import the library.
The IDE will unzip the file; you don't have to.
If the program fails to upload, make sure the Arduino
board type is correct and the COM port is correct. If that
doesn't work, unplug the LCD and try again (a good
reason not to solder it together).
The Arduino IDE saves programs in its folder within a
new folder with the program name. This can be confusing
when you are moving things around. NV
April 2015 27
■ PHOTO 5.
■ FIGURE 1.