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I have got the SparkFun kit with the AD8232. The schematic is:

enter image description here I wish to use only 2 leads; how do I ground the third lead RLD? I'm collecting the signal from the hands. The datasheet only gives application for cardiac monitor wherein the electrodes are placed near the heart. Can someone give me an idea? My first option was to connect two \$10\:\textrm{M}\Omega\$ resistors from RA (-IN) and LA (+IN) and then from the other end connect it to RLD. However, this is not producing optimum results.

Simon Marcoux
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Richeek Dey
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  • You should provide links to devices mentioned. | It depends what you are trying to do. If you are trying to monitor produce an ECG waveform that bears a reasonable resemblance to the ones used throughout the medical world then you should use multiple leads and connect then 'correctly'. If you are trying to produce an interesting waveform that has an unknown relationship to normal ECGs and which is of unknown meaning and usefulness for normal purposes then any connection that pleases you is fine.... – Russell McMahon Jul 12 '16 at 11:33
  • ... You say "not producing optimum results" - it will not produce NORMAL results, of course. Please explain what you consider is optimum and what you actually do get. – Russell McMahon Jul 12 '16 at 11:33
  • You can do better. You need to say why you need to use hand-hand- only, what you are attempting to achieve, what you have tried and what is wrong with the results for your uirpose. This is an EE focused site and we almost certainly can help but if you rely on people having to know the underlying medical aspects in depth you may miss valuable help from people more versed in the electrical issues. I have added some material to my answer BUT you need to and obviously are able to add more information that will help us help you. ... – Russell McMahon Jul 12 '16 at 12:43
  • I assume you have attempted to apply Eithoven's triangle and work backwards to deriving how Lead III and ground (both missing ) can be derived. What did you use to do this? What was wrong with it? What sources did you use? ...? || Presumably you have attempted to derive results from the Einthoven's triangle vector relationships as in eg [top of page 2 here](https://www.biopac.com/wp-content/uploads/BSL_l06_BSL_4.pdf) Yes? Can you show us your calculations/thoughts/figurings? ...? – Russell McMahon Jul 12 '16 at 12:48
  • See update answer. The Cornell student lab looks VERY apposite with some good leads. – Russell McMahon Jul 12 '16 at 13:08
  • You can get away with almost no signal quality loss when measuring the signal from the thumbs. Although, RLD is still advisable. – ammar.cma Jul 31 '17 at 23:06

2 Answers2

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Not sure if you're still looking for a solution to this, however this is what worked for me. If you short the 1nF capacitor from RLD to RLDFB this switches the module into two lead mode. For more info check page 17 of the datasheet.

https://cdn.sparkfun.com/datasheets/Sensors/Biometric/AD8232.pdf

Hope this helps.

Shay
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You should provide links to devices mentioned.

ECGs are industry standard waveforms of heart activity that are based on industry standard means of acquisition. If you use non standard means you will get a non standard waveform in a given situation.
Whether this is useful depends on what you are trying to do.
Whether this can be optimised depends on what you consider is optimum.
Can it produce an entirely standard result? - No.

ie it depends what you are trying to do.
If you are trying to produce an ECG waveform that bears a reasonable resemblance to the ones used throughout the medical world then you should use multiple leads and connect them 'correctly'.

If you are trying to produce an interesting waveform that has an unknown relationship to normal ECGs and which is of unknown meaning and usefulness for normal purposes then any connection that pleases you is fine.

You say "not producing optimum results" - it will not produce NORMAL results, of course. Please explain what you consider is optimum and what you actually do get.

Hand to hand only, 2 electrode ECGs:

The following relate to 2-hand only ECG systems.
To better determine their relevance to the OP's kitset and IC the OP would ideally provide links as requested.

This 2014 Cornell university student assignment sheet ECE 5030 - ECG recording from the hands. provides a wide variety of references and comments on implementation of a 2-hands ECG system.

This 1985 IEEE pape
A Real-Time QRS Detection Algorithm
appears to be at the heart of their system

Einthoven's triangle introduction and practical lab stuff here

Excellent Eithoven's Triangle simulator to assist visualisation - should be useful in this context for others more versed in EE than ECGs.
A simple device to illustrate the Einthoven triangle

Should be useful:

Video ET intro

Comparison of Heart Vectors Calculated with Different Systems of Leads
About 1950 vintage. Looks good.

  • Einthoven's equations for the heart vector are based on the assumption that voltages measured across the trunk horizontally (or vertically) are proportional to the horizontal (or vertical) component of the dipole moment of the heart's electromotive forces. One necessary consequence of this assumption is that all the horizontal (or vertical) voltages be similar, and that heart vectors calculated with different sets of these voltages and appropriate formulas be the same. An experimental test of this predicted result is described in this paper.

While this is about attempting to detect, identify and correct for the effects of lead reversals post-priori it may be useful due to its detailed examinations of what you see and why and what can be done about it.
ECG limb lead reversals

It is highly likely that this image based search output will more easily lead to useful results than text based results.

May be useful:

Development of a 2 lead ECG program 1982 (2 lead = 3 electrode?)

BIOPAC Application Note 109 1-, 3-, 6- and 12-Lead ECG

Not as good as it sounds, alas. Uses sequential 1 lead BUT has some insights How to use 1-lead ECG recorders to obtain 12-lead resting ECGs and exercise ("stress") ECGs

Unveiling the Biometric Potential of Finger-Based ECG Signals 2011

EKG book

A comparison of 2-lead, 6-lead, and 12-lead ECGs in patients with changing edematous states: implications for the employment of quantitative electrocardiography in research and clinical applications.

Other:

Tutorial 12 lead ECG Primer: The Leads of a 12-lead ECG

standard 12 lead set

ECG basics](http://en.ecgpedia.org/index.php?title=Basics)

Wikipedia basic ECG

and

Interesting:

iPhones and Eagles

And other apps

Russell McMahon
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  • I do not need a full 12 lead ECG which is "industry standard". What I meant when I said its not producing optimum results is that as compared to a 3-lead ECG wherein there' the lead from right arm, left arm and right leg; the signal isn't as good. However, based on studies removing the RLD shouldn't have an impact on the ECG signal itself but rather the common mode signal. And that is what I'm trying to find out; to remove the common mode noise AND not use RLD. Its tricky I know, but its possible. – Richeek Dey Jul 12 '16 at 12:02
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    @RicheekDey: RLD is not for "removing common mode noise", but to prevent the common-mode component from slowly accumulating so much that it saturates the amplifier inputs with respect to your system ground. Another way to overcome this is to allow system ground to float, with a high impedance path to the subject to ensure that it tracks the body potential **WITHOUT exceeding safe levels of DC current**. There's a lot of overlap between this and ESD protection. I cannot stress enough that you should not be making your own ECG equipment unless you thoroughly understand electrical safety. – Ben Voigt Sep 10 '16 at 15:41
  • @BenVoigt, that doesn't seem accurate. RLD improve CMRR. – Scott Seidman Oct 10 '16 at 19:36
  • @ScottSeidman: Systems lacking RLD absolutely are prone to saturation and clipping (Speaking from personal observation). You cannot just propose another way of filtering common mode noise, because you will still suffer clipping. – Ben Voigt Oct 10 '16 at 19:39
  • The technique was developed to improve CMRR, I believe by Webster in the early '80s. The IEEE Trans BME Paper does not mention saturation, though of course it does that as well. I just used it on a 32bit design, where I couldn't care less about saturation, and it reduced my noise by a factor of about 2-3 – Scott Seidman Oct 10 '16 at 20:09