The Scientific American article was called "Home is where the ECG is" and can be found at http://www.sciam.com/article.cfm?articleID=000C74E 4-5172-1C74-9B81809EC588EF21 . It's a very good article, except that it relies on the AD624AD, which is expensive. The 624AD is overkill--I have personally built the same project with a lesser chip, with fine results.
I attempted to build one of these a few years ago, beginning with the SciAm article, but found that the 624AD was out of production at the time. I checked around with the other big semi companies, and eventually got Linear Technology to send me a few free samples of their low-noise instrument amplifier, the LT1167. (http://www.linear.com/prod/datasheet.html?datashe et=437)
I used it with a gain of 1000 (it can be raised to as high as 10000), inside a metal biscuit tin, with the two differential inputs from the left and right wrists, and a ground on the ankle. For power I used two 9V batteries with the + of one and - of another tied to ground to produce +9 and -9 V. Using some thin coax cable for the leads reduced noise, as did commercially-manufactured EKG electrodes and gel.
In the end my DIY "bioamplifier" got me a very clean EKG-type trace into a digital storage scope. Because it didn't have any isolation, optical or otherwise, I never hooked it up to anyone except myself, but for the one or two times I had to demonstrate it, it worked like a charm.
It also worked as an EMG, with the gain dialed down a bit I could put both leads on my bicep and then flex to produce a signal on the 'scope. I never tried it, but I think up at the higher end of its gain range it could probably do crude EEG as well.
Cheers,
KB1JMV
Slashdot Mirror
The Scientific American article was called "Home is where the ECG is" and can be found at http://www.sciam.com/article.cfm?articleID=000C74E 4-5172-1C74-9B81809EC588EF21 . It's a very good article, except that it relies on the AD624AD, which is expensive. The 624AD is overkill--I have personally built the same project with a lesser chip, with fine results.
I attempted to build one of these a few years ago, beginning with the SciAm article, but found that the 624AD was out of production at the time. I checked around with the other big semi companies, and eventually got Linear Technology to send me a few free samples of their low-noise instrument amplifier, the LT1167. (http://www.linear.com/prod/datasheet.html?datashe et=437)
I used it with a gain of 1000 (it can be raised to as high as 10000), inside a metal biscuit tin, with the two differential inputs from the left and right wrists, and a ground on the ankle. For power I used two 9V batteries with the + of one and - of another tied to ground to produce +9 and -9 V. Using some thin coax cable for the leads reduced noise, as did commercially-manufactured EKG electrodes and gel.
In the end my DIY "bioamplifier" got me a very clean EKG-type trace into a digital storage scope. Because it didn't have any isolation, optical or otherwise, I never hooked it up to anyone except myself, but for the one or two times I had to demonstrate it, it worked like a charm.
It also worked as an EMG, with the gain dialed down a bit I could put both leads on my bicep and then flex to produce a signal on the 'scope. I never tried it, but I think up at the higher end of its gain range it could probably do crude EEG as well.
Cheers,
KB1JMV