Discuss this article in the Nuts & Volts forums at
dieter that it's time to nibble
on a carrot.
New to Propeller or
Arduino coding? Not a
problem. You'll find sample
Arduino and Propeller code
for all of the sensors in the
There's also a moderated
forum at Parallax and an
email hotline to military
medical experts with TATRC
who can discuss project
concepts with you.
You'll notice the fresh strips of pH paper are green —
meaning a neutral pH of 7. If you handle the strips directly
with your fingers, the paper will discolor to indicate the
pH of whatever is on your hands. So, use tweezers to
handle the strips, and keep the strips sealed in an airtight
plastic bag when not in use.
The ColorPAL is an easy to use, three-pin device:
power, ground, and signal. The hookup is hardly worth a
schematic, as there are no pull-up resistors or other
external components required. The sensor — based on an
Atmel ATtiny13A, 10-bit analog-to-digital converter (ADC)
— plugs directly into the Board of Education breadboard,
but I prefer to use a servo extension cable, like the one
included with the kit.
Ideally, you'd have
several standard pH
solutions to calibrate the
strip color to actual pH.
Alternatively, a calibrated
digital pH meter would be
great to have as a standard.
For our purposes, let's
assume that the printed color guide is accurate.
So, for your first experiment, check the pH of your
urine. Then, go load up on water and after about 20
minutes, check the pH again. What's the effect of diluting
urine on pH? Now, repeat the test after chugging down a
few cups of dark coffee. Any change? How about after a
tall glass of cranberry juice? Or, a protein-rich slab of beef
or fish? Or, after a five mile run in the sun? Do you see a
pattern? Can you see applications?
For example, what about a dehydration alarm based
on urine pH since a lower than normal pH is consistent
with dehydration. Or, how about an 'over-the-top'
ketoacidosis alarm for dieters — or soldiers recovering
Figure 4. ColorPAL sensor, pH color guide, and booklet of pH paper strips.
To prototype the project concept, I started with the
ColorPAL Sense (Spin) code from the Parallax ColorPAL
product page. The sample code returns the raw RGB
values of color detected by the sensor. If you want to have
a digital readout of pH, then you can set up a table to
map, for example, the red-orange printed on the pH guide
with a pH value of 1. The LED readout that comes with
this kit would make a nice digital pH display. Or, you can
map the RGB values at a trigger point — say, the light
green associated with a pH of 5 with a buzzer or flashing
LED. The resulting ketoacidosis alarm would remind the
48 February 2013
As you can see, there's a LOT in the kit for a team of
students, much less a single experimenter to explore. I've
only touched on one of over a dozen sensors in the box
of goodies and yet have a working clinical device capable
of practical application at home or — as the contest
designers intend — in the battlefield.
If you check
learn.parallax.com, you can read
through a list of project ideas, as well as full project
examples with source code. I can't wait to see what sort
of innovations the contest will foster. So, what are you
waiting for? Get your hands on a kit. NV