I measured the voltage increase of batteries as
they got colder, and created a voltage vs.
temperature plot. Using a linear voltage ramp, I
was able to plot the I-V curve of different diodes
and match their response to Shockley’s diode
equation to better than 1% accuracy.
I paid the huge sum of $15,000 for it. Now, I
can build an even more powerful instrument with
an Arduino, a shield, and freeware software for
less than $100. It measures four input voltage
channels at 16-bit resolution, and up to 40,000
samples per second directly into Excel. Once
there, I can plot the data in any format I want.
This is a high performance general-purpose
instrument that has become the Swiss army knife
of my home lab. It is my go-to instrument to
measure, record, and display data in just about
every experiment I do.
I use it as a data logger, a strip chart recorder,
and as an audio signal analyzer. I built a vibration
analyzer to measure the impact of
damping materials for a fan (see
Figure 1). With it, I built a micro
ohmmeter to measure the typically 20
µΩ contact resistance of a solder joint.
I built a noise spectrometer to
measure the excess 1/f noise in
carbon resistors. I turned it into an
impedance analyzer, and fit simple
LRC models to the measured
impedance profile of any component. I
measured the voltage increase of
batteries as they got colder, and
created a voltage vs. temperature plot.
Using a linear voltage ramp, I was able
to plot the I-V curve of different diodes
and match their response to
Shockley’s diode equation to better
than 1% accuracy.
These are just some of the measurements this
instrument can do. Here’s how you can build this versatile
precision data acquisition system.
The Arduino Due
The Arduino family of microcontrollers and boards
come in a wide range of price, performance, and form
factors. They each have their plusses and minuses. Most of
us start out using the Arduino Uno because it is simple,
cheap, and readily available. However, when it comes to
performance and board size form factor, my favorite
Arduino is the Due (Figure 2). I like the Due for three
reasons: performance, memory, and form factor.
The Due uses a 32-bit Atmel ARM Cortex M3
SAM3X8E CPU with an 84 MHz clock. This is compared
to the eight-bit and 16 MHz clock of the Uno. The
combination of higher clock frequency and 32-bit
operation means some functions can be more than 20x
faster with a Due.
The Due has much more memory, which means larger
programs can be written and larger data arrays can be
used. A sketch is stored in the Flash memory, while
variables are stored in the SRAM memory. The Due has
512K of Flash as compared to the 32K in the Uno, and it
has 96K of SRAM compared with 2K in the Uno. I have
never written a sketch that runs out of memory on a Due.
When collecting data, the SRAM is important as this is
June 2017 15
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■ FIGURE 1. Example of a crystal microphone with its foil
removed, mounted to a fan. The voltage from the PZT wafer
picks up vibrations. The graph has 1,000 measurements during
the 90 milliseconds.
■ FIGURE 2. The Arduino Due with the standard Arduino pin
configuration, plus extra pins.