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Wanted: Medical sensor isolation circuit using optocoupler

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quietmedic

New Member
Hey all. I'm looking for an isolation circuit for the device described on this page: The Story of My ECG.

Basically, it is a simple EKG (electrocardiograph) that interfaces with your computer sound card via standard 1/8" audio, and obtains your readings via 3 custom electrode leads placed on patient's chest.

As the author himself states, the unit is generally safe BUT in event of some catastrophic series of failures, there is nothing preventing your 120V AC from inadvertently transmitting down the electrode lead, potentially killing the patient. He suggests a linear optocoupler for isolation, but does not post one.

So: would anyone be kind enough to suggest a simple analog linear optocoupler circuit that can be used for this project? (I know basic electronics but am nowhere near good enough to design a real circuit based on the datasheets for typical stuff like the LOC110)...perhaps there are already circuits of this type on this forum or online...just don't know where to look or what would have the proper specs for this application.

Thanks in advance for any help..
 

Hero999

Banned
I suggest you shouldn't buiild this unless it's only for fun - medical equipment needs special approval before it can be used.
 

Papabravo

Well-Known Member
I don't know for certain weather a linear optocoupler is physically realizable. I have my doubts. The other possibility is using a pulse transformer.
 

crutschow

Well-Known Member
Most Helpful Member
Many semiconductor companies specifically prohibit the use of their components in medical electronic devices unless you obtain special permission from them to do so.
 

Leftyretro

New Member
It certainly can be realized, but the optical isolator would just be one component in such an application. This application is dealing with very low signal levels and has to be designed with low noise and high common noise rejection.

Because of the low signal strength there will most likely have to be some amplification performed before routing the signal with enough voltage/current required for going through an optical isolator. This implies a power source for the sensor circuit prior to the isolator, most likely low voltage battery(s). While most optical isolators are used in on/off switching mode, it's just a matter of proper DC bias and signal injection to pass an analog signal through such an isolator.

You could most likely get ALMOST as much isolation safety using small signal transformers between the signal probes and the existing amplifier circuit. However proper specifications and locating them will not be a simple task.

As many have implied, it's kind of important that you share your intent for such an application. If it's just for your personal use, experimental much as the link you posted from, that's one thing. If it's for use on others or for general sale then you really need to learn about all the legal requirements.

Lefty
 

Papabravo

Well-Known Member
It certainly can be realized, but the optical isolator would just be one component in such an application. ...
How about a link to a datasheet if you have one in mind.
 

Leftyretro

New Member
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