Portable 3-lead Electrocardiograph

I am not a medical professional. Construct and use this device at your own risk.

Introduction:
 
In this instructable I will demonstrate how to make an electrocardiograph (EKG) for monitoring your hear rate via leads taped to your skin. The output will be used to switch an LED on and off with each detected heartbeat.

All circuit components can be found at Radio Shack. The total cost of this project is around $30.

Estimated completion time: 5 hours

This project may be too difficult for anyone unfamiliar with the operation of a multimeter and its use in basic troubleshooting of electronic circuitry.

Uses:
   - Biofeedback: Learn to manipulate your heart rate at will and monitor its reaction to your
       thoughts and behavior. Wikipedia: Biofeedback
   - Relaxation: Focus on bringing your heart rate down when stressed. The rest of your
       body will follow suit.
   - Decoration: Can be integrated into a costume. Pulsing Iron Man arc reactor anyone?

How it works:

This circuit detects and amplifies the electrical impulses generated by your heart with each beat. Your skin acts like a giant antenna, picking up a lot of noise and interference so a differential amplifier is employed to effectively cancel any unwanted input.

The differential amplifier has two inputs relative to a common ground. Any voltage that is common to both inputs will be effectively ignored while any difference in voltage between the two (i.e. the polarization of your heart muscles) will be greatly amplified.

I will be using this device for biofeedback and ornamentation so I will not be exploring all the complexities of an EKG output. However should you wish to see an EKG in all its glory, the output of the differential amplifier portion of this circuit can be connected to an  oscilloscope and should permit you to see (untested) all the features one would expect. However, as a commenter mentioned one should never connect an amateur circuit that is connected to your body (particularly your heart) to your household power lines. If you wish to employ an oscilloscope use a battery powered device or take steps to electronically isolate the circuit from the oscilloscope.

I just want a device that blinks every time my heart beats. To give clean pulse I have added a monostable timing circuit to the differential amplifier output that turns the signal into a square wave with an adjustable width.

More information that may be helpful in understanding the details of this circuit can be found below.

Wikipedia: Differential Amplifier
Wikipedia: Electrocardiograph
Scribd: Monostable Timing Circuit (p. 6)

Step 1: Tools and Materials

NOTE:This instructable is separated into two parts, the circuit and the enclosure. You should have no problem acquiring the parts to make an exact reproduction of the circuit. However, I used a number of items I had laying around or that I pulled from broken equipment to make the enclosure. The enclosure has no bearing on the function of this device and is used only for ease of transport and cosmetic purposes. The techniques used to make the enclosure should be applicable to similar items. Using a small amount of ingenuity and you should have no trouble making an enclosure similar to or superior to mine.

Required For the Circuit:
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Tools:
Soldering Iron (Craftsman)
Wire wrapping tool
Wire Strippers
Multimeter (Craftsman)
Sandpaper
Lighter or Torch
Small Flat-head screw driver
Solderless Breadboard
Marker
Duct Tape

Materials:
Solder
Solder Weld (optional)
Wrapping Wire
Wire - 24AWG
(3) Pennies

Circuit Components (all found at Radio Shack):
Super Bright LED
555 Timer IC
LM324 Quad Op-amp IC
2N3904 Transistor (NPN)
9V Battery Connector
9V Battery
(2) Dual position terminal blocks
SPST Switch
Circuit Board (with sufficient space for you to work comfortably)

Capacitors
   (4) 10 uF Electrolytic
   (1) 100 uF Electrolytic
   (1) 1 uF Electrolytic
   (1) 47 uF Electrolytic
   (1) 470 uF Ceramic
   (6) 0.1 uF Ceramic
   (1) 0.01 uF Ceramic

Resistors
   (2) 100k Potentiometer
   (1) 4.7k
   (2) 10k
   (3) 10M
   (1) 47k
   (4) 100k
   (1) 470k
   (1) 1k

Required For the Housing (optional):
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Tools:
Casting Resin (Alumilite)
Phillips-head screw driver (Craftsman)
Dremel Tool
Drill Bits
Nibbler

Materials:
Project Enclosure
Ruler
Hot Glue Stick
Lighter or Heat Gun
Assorted Camera Parts or Metal Pieces (be creative)
Styrofoam Scraps
Cargo strap like those found on a laptop bag
(2 Pair) Small Nut & Bolt
(3) Machine screws
(2) D-rings with clips
(4) Phillips-head screws
(4) Threaded Standoffs that can mate with the above screws

Comments

[Revanchist]

Watch out also with the gain of your amplifier... Too much and you'll get some feedback shock which may cause macro and microshocks.... Use an isolation circuit just in case even though its using a 9 volt battery....

A good example could be an iso124 or similar.... If you feel tingly or light headed, your gain is too high.....

Also, you could have used an instrumentational amplifier instead of the differential amp... But only for more advanced circuitry or applications....

Great job! I built one a while ago I've been meaning to make an instructable....
Cheers

[xiaoxiao051585]

cool
After reading, I want to make it by myself.
I need a big version of schematic.My email :[e-mail].
Thank you very much!

[lw119]

Just click the i in the top corner of the image and you can see it full size.

[snotty]

Cool,

Last time I tried this it worked once, sort of and then never really worked again...

Hopefully this one will be less finicky for me.

[lw119]

So far it's been pretty reliable for me. Getting the gain just right can be a pain the first time and electrode placement can be a huge factor in how clear your signal is and how sensitive it is going to be to your muscle contractions. Good luck!

[snotty]

Yeah,

I was planning to hook it up to an arc reactor thingy. Mine is started with a ring of LEDs that fire individually in rapid succession: http://www.instructables.com/id/How-to-make-a-4017-Decade-Counter-Run-for-One-Cycl/

If I ever get around to it, mine will be made from bicycle gears, bone and teeth. And if I get really fancy it might be wirelessly connected to the electrodes.

Also, do you use any conductive fluid for your electrodes? Some sites say they need it.

[lw119]

I just use if directly on my skin but I am holding still. I think if you were to use it as part of a costume you would definitely want to spring for the adhesive pads with the conducting gel. You can see in my video on the last page how it reacts too much movement. I think I am going to add that.

[snotty]

I made some decent conductive gel with salty shampoo. Some people use shampoo alone.

Sports-type heart rate straps can work with or without conductive goo.

[lw119]

I will have to give that a try. Thanks.

[xantor]

Just one thing for safety: You mentioned connecting it to an oscilloscope.

Never Ever connect anything that is connected to the mains while there are wires connected to your body, especially to your heart region...

If you insist on using a scope, use a battery pack to power it or at least an isolation (1:1) transformer to mains.

You really don't want a failed circuit to put line voltage on that coin on your heart while standing on a tile floor barefooted...

[lw119]

Very good point. Since I only mentioned it in passing and did not go into detail about using an o-scope or highlight the safety requirements thereof, I think I am going to just edit that part out, least someone inadvertently turn their EKG into and automated external defibrillator. Thanks for commenting.

[AshTheBuilder]

I was looking for something like this for a project I am working on. Your instructions are very detailed and easy to follow. Thank you.

Couple questions though. In your video showing the flashing red LED in the "top hat" you have a test setup with just the timer part of the finished circuit but you have what appears to be a large capacitor in parallel with the LED to give that nice rise and fall in intensity. This didn't make it into the final circuit but I think I might want to include it. Is there any reason why you left it out and why I should too? Also, why did you switch to a white LED? The red one in the video looks amazing.

[lw119]

Yup, that's a 1500uF capacitor that I added on a whim when testing the LED mount. I am not sure why I left it out of the final circuit and now that I think about it I might have to go back and add it. You might have to change the resistor value to maintain the LED intensity but I have a feeling you know that already.

As for the color change, I was being careless and broke one of the leads on the red LED and the only other LEDs I had on hand were white and IF. IF would have looked cooler on the instructable but not so much in real life lol.

Thanks for your comment and I hope your project is a success.

[AshTheBuilder]

Thanks for the reply!

Tough break on the LED (no pun intended). I am afraid I am missing something though. Why would the infrared LED look better? Wouldn't be invisible?

[lw119]

Most digital cameras are sensitive to infrared but they read it as a bluish white. It's a handy trick for checking the batteries on your TV remote (pictured below) or any other IF source.

[iminthebathroom]

Cool, my medical background and tinkering nature are pleased!

[lw119]

Glad to hear it!

[cpotoso]

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[lw119]

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[afbcom]

"We have a "be nice" comment policy. Please be positive and constructive with your comments or risk being banned from our site."
^^

As a first year electrical engineering student, that circuit took ~10 seconds to breakdown and see exactly what he did.
The path crossing is minimal, and I dare say for someone with a PHD in Electrical Engineering, child's play.

Enough of the negativity...
Awesome instructable, well documents. =D

[carlos1w]

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[cpotoso]

(removed by author or community request)

[lw119]

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[VadimS]

His schematic goes suck, but still understandable. His reply was a bit negative but pails in comparison to your own.

[M4industries]

Am I the only one who sees a resemblance of the Ubuntu logo in the thumbnail?

[lw119]

Now that you mention it I see it too, lol.

I pulled that part from a broken Technicolor camera from the 50s.

[VadimS]

This is really cool. Just had a look around and I've got the parts to build it (or one vary similar). So guess what I'm doing this weekend. lol

[lw119]

Awesome! I'd be interested to know how it goes.

[VadimS]

I got buisy, so didn't get a chance till now. The schematic is almost eligible (instructables re-sises the images) could you host it on image shack or something and provide a link?
Thanks.

[lw119]

You should be able to click on the box (with the i) in the top left corner of the image and it will give you the option to view the schematic in its original size.

But to make things easy: LINK

[lw119]

Easier to follow version: Link

[VadimS]

Wow I've bean roaming instructables for years and never looked twice at that symbol, thanks.

[lw119]

No worries, glad I could help!