Electronics > Projects, Designs, and Technical Stuff
EKG front end circuit
(1/3) > >>
Wimberleytech:
I started this a few years ago but never finished it.  Now that I am dealing with some issues, I decided to get it to the next step.

The circuit is pretty simple, using and AD624 inamp, followed by two second-order Sallen-Key LPFs...and a gain stage.  Turns out the best quality signal is output from the first filter.  You need enough bandwidth to handle the QRS pulse with enough cutoff to knock out 60Hz.

Baseline wander is troublesome when just trying to get a strip holding the inputs with left and right hand...it is doable but not user friendly.  When actual sensor pads are attached to the chest, I get a very nice waveform.  My pads are old, so I rejuvenate them with a salt-water solution.  Fresh ones would likely perform better.

If I decide to take this further, I will probably move to a different lower-voltage inamp operating from a single supply. 

For now, what I have does the job.

tpowell1830:

--- Quote from: Wimberleytech on October 26, 2018, 10:05:41 pm ---I started this a few years ago but never finished it.  Now that I am dealing with some issues, I decided to get it to the next step.

The circuit is pretty simple, using and AD624 inamp, followed by two second-order Sallen-Key LPFs...and a gain stage.  Turns out the best quality signal is output from the first filter.  You need enough bandwidth to handle the QRS pulse with enough cutoff to knock out 60Hz.

Baseline wander is troublesome when just trying to get a strip holding the inputs with left and right hand...it is doable but not user friendly.  When actual sensor pads are attached to the chest, I get a very nice waveform.  My pads are old, so I rejuvenate them with a salt-water solution.  Fresh ones would likely perform better.

If I decide to take this further, I will probably move to a different lower-voltage inamp operating from a single supply. 

For now, what I have does the job.

--- End quote ---
bradicardia?
t1d:
Excellent, WT! I have played around, with these type circuits, a bit, myself. What I discovered is that they use the exact same technology as lie detectors. So, I began to include those circuits, in my web searches, too. Additionally, component manufacturers are beginning to offer HIDs, that interface better with individual, portable and DIY units. The major on-line component suppliers are beginning to carry those parts. Adding respiration rate and sweat detection are not very complicated and give the doctor even more/better information.

Great project, on the assembly! Do well. Keep us informed.
SiliconWizard:
I'd suggest adding some input protection.

As a side note, you could take a look at the AD8232 which packs a lot of features.
Wimberleytech:

--- Quote ---bradicardia?

--- End quote ---

PVCs
Navigation
Message Index
Next page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod