Homemade EKG

ekg.jpgReady to make your own homemade Electrocardiogram (ECG or EKG)? This machine will output your heart signals to the screen of your computer. Using plans found on the net and a little elbow grease it's actually quite simple.

First of all, to avoid any confusion: I am not an electrical engineer. I studied International Politics and Latin American Studies in college. I'm trying to break this down so that it's simple enough for pretty much everyone to understand. The project is documented here, where we got the basic idea for this project... but I want to break it down a little differently.

Shopping list:

Shielded Wire (to connect electrodes to body)
extra wire (to connect parts)
1/8" male to male cable
9v battery
9v batter connector
3x LF353 Dual Op-amp
12x 100k ohm resistor (1/4 watt)
8x 10k ohm resistor (1/4 watt)
1x 1uF capacitor (needs to be ceramic - helps to filter out high frequency noise)
1x .1uF capacitor (needs to be ceramic)
6x 1N4001 diodes
1x 1/8" female plug (can use whatever size really)
3x electrodes (pennies work but ask your local hospital if they'll give you some of the real 3M red dots, they gave them to us)
Project board

Download and install the EKG program (basically an oscilloscope)

Ok, now you need to assemble this according to the schematic. For beginers this can look like a daunting task but don't worry, it is very doable. I looked at the schematic and there were parts that I didn't really understand so I redrew the whole thing so that it made sense to me and researched the components that I didn't know too much about.

I'm including my hand drawn schematic for reference if you want to check it out. (yes I know there are free programs to draw schematics, but again, I wanted it to make sense to me)

After it's all assembled you need to hook it up to your test subject... but wait! This is a potentially dangerous setup. You will plug your EKG into your computer and that is plugged into the wall. In a worst case scenario you could send 120 volts ac across your heart. This is bad. I'm not saying this will happen, this is just my disclaimer.

The first time Sam and I tested it, we had it hooked into a laptop and also reasoned that we are only three blocks from a fire station so the paramedics could get here pretty quick (Flawed reasoning? perhaps). But by unplugging the laptop and running off of the battery, we figured we reduced our chances of an accident.
Ok, so you take the shielded wire, cut three lengths of it and hook them into the EKG where it says in+, in-, and body. (The two in- points need to be linked.) The in+ and in- are connected to either side of your chest (doesn't matter which one goes where) and the body lead is connected anywhere on your body but your chest. If you are using pennies as your electrodes, use a little bit of shampoo as a conductive gel to better the contact with your skin.

Make sure your 9v battery is connected and then using a 1/8" male to male cable, plug your EKG into the mic input on your computer. Mute everything else on your computer and make sure that the mic is selected as your input device. Run the EKG program and press 'start recording'. It should work.

There have been a lot of suggestions of ways to improve/change this design. We haven't had time to try them all out but here are a few:

  • Use optical isolators to eliminate the risk of fibrillating your heart!
  • Use a wireless guitar setup to isolate the EKG.
  • Build a robust and shielded EKG that doctors in third world countries can use.
  • Hook the EKG into a digital recorder so it is portable and then play it back into your computer.
  • Use different software

We would like to try some of these as time permits but feel free to post your ideas and results.

Resouces to better understand the components:

Once you're getting results, it's time to learn how to interpret them. Here are a few resources to try.

Here's our adventure making our first one.

Go ahead and email me with questions.


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