Home Is Where the ECG Is
Watch your heartbeat with do-it-yourself equipment, as described
I fashioned my first electrodes out of quarters that had been smeared with a conducting layer of shampoo, taped firmly to my
body and connected to wire leads. They worked. Then I discovered that anyone can buy bags of 50 of the real thing: the self-sticking electrodes used by
cardiologists. The cost is about $13 on-line from www.medicalbuyer.com (part no. 9641). Just peel and stick. I
terminated the signal wires with alligator clips to grip the metal nipples on the backs of the electrodes.
negative lead to your subject's left wrist, the positive lead to the right wrist and the ground lead to the left shin just above the ankle. It proved a bit
cumbersome to operate test equipment with my wrists wired up, so I attached the right and left leads just below my armpits and ran the wires under my
clothes and out just above my belt buckle.
The bouncing ECG trace makes a delightful display for any oscilloscope.
Oscilloscopes are essential for any electronics hobbyist, so if you don't already own one, you should. Dealers of electronics surplus equipment sell two-channel
scopes with sweep speeds of 100 megahertz--far faster than you need for a simple project such as this--for about $250. And you may be able to find even better
bargains through on-line auction sites like eBay or at ham radio flea markets, called hamfests, run by local ham clubs. If you're on a tight budget, you could
build a cheaper monitor; for suggestions, check out the discussion about this project on the Society for Amateur Scientists's Web site.
If you want to digitize your heart traces for computer analysis, you'll need an analog-to-digital converter that can sample at 100
hertz or better--that is, at least twice the largest signal frequency. Both Vernier Software and National Instruments sell such units. Serious amateurs should consider NI's extensive line of software, which offers turnkey
solutions to just about every data acquisition and analysis challenge there is. Though pricey, these packages can change your life as an experimenter.
For more information about this and other experiments for amateur scientists, check out the Society for
Amateur Scientists's Web site. As a service to the amateur community, SAS will provide the electronic components only, including the electrodes (but no
circuit board or project box), for $60. You can write the society at 4735 Clairemont Square PMB 179, San Diego, CA 92117, or call at 619-239-8807.