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Issue
99, October 1998
X-Y Graphing Data
Logger
by
Alberto Ricci Bitti
With
more data than he can handle (and always in some inconvenient
place), Alberto constructed a powerful, handheld, programmable
data logger from his Casio pocket calculator. And as a reward,
Design98 judges made it their "first PIC.
Start
• Machine
Muscle
• Using
Componentware
• Low-Power
Guys
• Flash
Risc Glue
• The Graphic
Engine
• Casio
Protocol
• Main
Code
• Inside
The Box
• Setting
up the Casio
• First
Graph
• Modeling
The Data
• Broader
Vision
• Software,
References & Sources
Like
any other designer, I have to cope with lots of data everyday.
Raw data in need of analysis comes from every design phase
and from all related sites. From writing specifications
to development, from production tests to on-site verification,
we end up with tons of measurements.
A
graph is often the best way to point out the key features
of what you measure. It’s useful for instantaneous
communications and easy to document for later reference.
It’s accepted for corporate quality system records,
too.
PCs
are powerful graphing tools, and maybe that’s why
almost all recent instruments have some kind of PC interface.
So, you just take out your dazzling new computer-interfaceable
meter, connect it to nearest PC, and start measuring.
Right?
Wrong.
Sometimes you want to take measurements in the field,
and you can’t take the instruments out of the lab.
Something other than the PC can collect the data, but
it’s fooled by grounding problems.
Other
times you need a battery-operated instrument, but a laptop
is too expensive, or it has to be used elsewhere, or the
batteries don’t last long enough. And don’t
forget that you have to convert data to spreadsheet format
to get the graphics.
What
if you need to collect data for a whole week? Can your
precious equipment be locked for such a long time?
My
solution: a simple yet powerful graphical data-acquisition
unit built from a pocket calculator. I applied a component-oriented
approach that resulted in a shortened development cycle
and overall quality improvement.
The
unit doesn’t just collect data. It also displays
it for further investigation, and it offers plenty of
analytical and statistical built-in functions.
I
applied low-power techniques and components to squeeze
all the power out of a 9-V battery. By the way, I’ll
also tell you how I found the communication protocol used
by the calculator.
While
this design doesn’t pretend to solve all your measurement
problems at once, it’s simple, cheap, and powerful
enough to be useful in the situations I described above.
Its
flexibility makes it ideal for acquisition in the lab,
on the production line, in the field, or wherever you
need a clear, graphical, and immediate (yet sophisticated)
data display.
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