Good morning Paul, First: I almost spilled my coffe as you bear a similar last name as a guy at a national research lab who does exactly such things :) Even when it makes your ECG preamplifier free for other things, I advise you to use another sensor and put a lot of decoding and interpretation to your brain. ECG is not easy from a safety standpoint, as it connects to the body immediately. The Signal is quite complex as it is composed of not a single but a "burst" of waves during excitation and contains a lot of moving and electrode artifacts, I wouldn't try to count BPM except AD conversion and doing a lot of filtering and preprocessing in software. I would use photoplethysmography instead of ECG, means you shine a little light from a LED thru your finger or ear to a photodiode. Actually a optocoupler with a bit of you inbetween ! The light at the photodiode will fade up and down with the local relative blood pressure in the tissue between the emitter and receiver, and so does the photodiode current. The resulting signal contains way less movement artifacts and less high-frequency parts. to record it on a PC i would say generate a audible AM-modulated tone with the photodiode current (amplified by an TIA) as modulation, when you feed that to the soundcard you can record with audacity and you will see the envelope on screen where you can count the (single) peaks per minute. For a more immediate result without PC, hook the TIA output to a V/F converter in the audible range and hook it up to a speaker, its easier to listen to the pitch changing. At work I am hooked up to heart-signal-analysing thingies quite often and i can tell you that it is easy to change heart-rate and relative blood pressure by will in a certain range. I made it a obligatory task to students, visitors and new co-workers to prove that they have a heartbeat ! :) Best regards Hendrik P.S.1.: My first post at the time-nuts P.S.2.: Don't let the FDA see anything :)

On 2/19/13 10:58 PM, Hendrik Dietrich wrote: > Good morning Paul, > > First: I almost spilled my coffe as you bear a similar last name as a > guy at a national research lab who does exactly such things :) > > Even when it makes your ECG preamplifier free for other things, I advise > you to use another sensor and put a lot of decoding and interpretation > to your brain. > > ECG is not easy from a safety standpoint, as it connects to the body > immediately. The Signal is quite complex as it is composed of not a > single but a "burst" of waves during excitation and contains a lot of > moving and electrode artifacts, I wouldn't try to count BPM except AD > conversion and doing a lot of filtering and preprocessing in software. Of course pretty much every elliptical machine, treadmill, and other exercise equipment has some form of ECG based measuring system, typically working off the handgrips. However, I'll agree that processing the signal is troublesome because of motion artifacts and the like. I've not seen a lot of algorithms for this, but the ones I've seen look a lot like NTP kind of filtering: you have an estimate of when you expect to see the next heart beat, so you time gate your signal to reject signals that occur too soon, or are missed. Missed beats just don't update the rate, and you use the beat to beat timing, inverted, to update the heart rate estimate, using some sort of exponential smoother (probably for implementation simplicity.. y(n+1) = 0.75*y(n) + 0.25*x(n) is something that a 8 bit micro can do pretty easily) > > I would use photoplethysmography instead of ECG, means you shine a > little light from a LED thru your finger or ear to a photodiode. > Actually a optocoupler with a bit of you inbetween ! > The light at the photodiode will fade up and down with the local > relative blood pressure in the tissue between the emitter and receiver, > and so does the photodiode current. The resulting signal contains way > less movement artifacts and less high-frequency parts. You can also do it with reflection. LED shines into your finger, and photodiode/transistor next to it looks the light coming back. You can use an off the shelf reflective sensor as used for things like limit switches. > Hendrik > > P.S.1.: My first post at the time-nuts > P.S.2.: Don't let the FDA see anything :) I've always wondered about how the exercise machines get around the "medical device" rules..