by Bryan Bergeron, Editor by Bryan Bergeron, Editor
Biology and Electronics
If you recall the experiment from your high school biology, Luigi Galvani found that electricity could animate the legs
of a dead frog. This simple experiment is worth noting
because the intersection of biology and electricity has come
a long way since Galvani’s experiments in 1791. Today,
medical and physiological electronics are multi-billion dollar
industries, and the tools for experimentation have never
been as affordable or easily obtainable.
to create a heart rate or breath rate display. Another option
is to pick up and teardown an inexpensive blood pressure
monitor from your local drug store. Can you figure out how
they’re determining pressure? You may have to search the
Web for details, such as how the sound of blood flowing
through arteries changes as external pressure is applied.
Then, there’s the kit approach. I’ve seen several
electrocardiogram (ECG) kits on the market. Ramsey
www.ramsey.com) sells one for about $50. If you’re familiar
with op-amps, want a great way to learn how to work with
op-amps and low level, low frequency signals, then build
your own ECG monitor. I’d take the precaution of NEVER
using an AC powered supply, even one of those low voltage
bricks. In addition, use an optical isolator to minimize the
chance that a voltage could be applied to your body as
you’re testing the circuit.
Of course, there are experiments you can perform in
which signals are intentionally sent to your body, as in
Galvani’s experiment. Again, have a look on eBay for one of
those abdominal toners that send pulses of electricity to
your ab muscles, causing them to contract. At the other
extreme — which I don’t recommend — are high voltage
tasers designed to temporarily stun.
If you’re into exercising and fitness, then you probably
know about the heart rate monitor pickups that work with
Polar watches, and many of the treadmills on the market.
This is another source of ‘teardown’ material that’s relatively
inexpensive — especially if you’re willing to tear open one of
the sealed sensors and replace a battery.
If you’re into optics and LEDs, there are dozens of
experiments that you can perform with an op-amp,
microcontroller, LED, phototransistor, and a handful of
discrete components. The simplest is a heart rate monitor
based on the reflection or transmission of red light through
your fingertip or earlobe. With each contraction of your
heart, red blood cells rush through the capillaries in your
fingertip. A phototransistor/op-amp circuit can detect the
resulting change in transmission/reflection of red light. Once
you’ve mastered heart rate, you can try your hand at blood
oxygen saturation (the more oxygen carried by a red blood
cell, the more red the cell). You’ll have to do a little research
to determine which wavelengths of light to use.
I’ve been working with a few simple sensors — a piezo
microphone element and a few resistive pressure sensors —
and an Arduino on a number of experiments. I use the
piezo element in my shoe to determine each time my shoe
strikes the ground — similar to the method used by the
popular Apple/Nike running sensor. The pressure sensors —
mounted at different locations under my running shoe insert