ECG - Page 1
Forum section: electronics / beginners

author: rthorntn
author_rank: Frequent Contributor
timestamp: September 20, 2012, 06:28:09 am
content: Hi,Sorry if this has been answered already.Does anyone have design for an ECG that outputs to a oscilloscope, if I could breadboard it that would be great?Thanks.Richard

author: Simon
author_rank: Unknown
timestamp: September 20, 2012, 06:44:36 am
content: Welcome aboard Richard. What is an ECG ?

author: firewalker
author_rank: Super Contributor
timestamp: September 20, 2012, 07:28:46 am
content: ElectroCardioGraph.There is some some designs online. I wanted to build one for the Tek's contest (I wasn't able to find a Tek, only Philips, Hameg and others). Tested by a model with minimum clothing on a treadmill.Alexander.

author: IanB
author_rank: Super Contributor
timestamp: September 20, 2012, 07:34:06 am
content: I presume electrocardiogram, aka heart monitor?There are doubtless many educational circuits to be found online for recording and displaying the electrical rhythm of the heart. However, attaching any electrical leads to the chest area is potentially dangerous and so great caution must be used to ensure the safety of the circuit. For instance, a typical oscilloscope is connected to the mains and while touching the probes (directly or indirectly) isprobablysafe, it is notcertainlysafe. In this situation you need something that is certainly safe.I don't have a circuit to give you, but if you find a reference to a circuit design you are considering then doubtless some members here can give informed comment on any potential dangers inherent in that circuit. Bear in mind that even voltages as low as 9 V in the wrong circumstances can prove fatal.

author: jeremy
author_rank: Super Contributor
timestamp: September 20, 2012, 07:56:01 am
content: Sorry, i can't paste on my phone for some reason. Google "biopotential amplifier" and hit the UNC.edu result. The book that chapter is from is one of the best on introductory medical instrumentation.These things can be really dangerous, please find someone to supervise you who knows what they are doing !

author: Kevin.D
author_rank: Frequent Contributor
timestamp: September 20, 2012, 11:32:19 am
content: I have built a few of these as kit's for experimenting with them ,there are quite few designs in magazines and around the web . The cheaper ones (they are not dangerous really as long as they are not mains powered of course and most are just pp3 battery powered diff amps).The cheap ones do work OK as long as you have good electrode pads ,the ones I have built are basically differential op amps circuit's with good common mode rejection and Lot's of low pass filtering to remove all the noise that is also present along with the microvolt level signals generated by heart muscle .Look here at the ad620 instrumentation amp data sheet to see a simple ECG usehttp://www.analog.com/static/imported-files/data_sheets/AD620.pdfHere's one of the Kit's I have built before ,this one comes with a small manual you can also download ,which will explain somethings for you .http://www.ramseyelectronics.com/cgi-bin/commerce.exe?preadd=action&key=ECG1C.It uses a cheap quad package lm324 to build a simple but effective filtered differential amp .

author: jeremy
author_rank: Super Contributor
timestamp: September 20, 2012, 12:12:24 pm
content: just some quick notes now that i am on my computer:electrode placement matters bigtime, as does having some electrolyte. Salt water might work, but see if you can buy ultrasound gel at the local chemist; often manufacturers make their gels dual purpose. As a starting point you should put the two differential input electrodes about 2/3 up on your pectoralis major across your body and then stick a third on your abdomen connected to 0V.I use meditrace electrodes but you can only get them in bulk afaik. Seeed seems to sell some:http://www.seeedstudio.com/depot/disposable-ecg-electrode-p-858.html?cPath=197You can buy expired packs on ebay sometimes, they won't hurt you but they won't work if the electrolyte has dried up. If you get AgCl or similar ones, keep them in the fridge when you aren't using them. If you know someone who is a nurse/doctor/clinical physio, get them to swipe you a few; they are consumables in hospitals anywayyou should put two opposite clamping diodes from the differential leads to ground (two on each input). There should never be more than 600mV across the electrodes with respect to GND, so these diodes will protect you a little in case of spikes.Use two 9V batteries to get +- supply.I'd recommend buying an instrumentation amp over building one. They come with laser trimmed resistors on the die and have pretty crazy common mode rejection as a result (the linked AD620 has 100dB, INA128s have 120db).Don't worry about the right leg drive stuff; I have a commercial ECG sitting on my desk right now and it doesn't even use it.If you are interested in seeing the R wave only, a lowpass at 35Hz is what you want. Diagnostic systems will have a ton of weird notches and stuff, but they have an overall lowpass of 100Hz usually.Any filters you use should be bessel, otherwise you will distort the signal. Bessel filters have a linear phase responsegood luck!

author: saturation
author_rank: Super Contributor
timestamp: September 20, 2012, 01:20:34 pm
content: If you need one for checking heart rhythms, all you need to know is normal versus not normal, these come premade on eBay.http://www.ebay.com/itm/PC-80A-HANDHELD-ECG-EKG-MINOTOR-WITH-CASE-WITHOUT-SOFTWARE-AND-LEAD-WIRE-/230850046428?pt=LH_DefaultDomain_0&hash=item35bfbc29dcOnce you know how to use them right, its very cost effective.

author: rthorntn
author_rank: Frequent Contributor
timestamp: September 25, 2012, 06:47:28 am
content: Thanks Simon, I have been eyeing these forums up for a while, google keeps sending me here and after a while I started adding eevblog in to the search fieldThanks everyone for the ideas, ultimately it was just a cool thing to do but the costs and the risks involved mean I have scrapped the idea. I mean I would use it once and it would gather dust after that.CheersRichard