Introduction: ElectroCardioGraphy (ECG) Wrist Straps / Electrodes
For a project that I was doing for university we were required to make two wrist straps and a leg strap that we could connect to another students left arm, right arm and the right leg.
The key points we will look at when making the wrist bands is to have the least amount of connection possible as the more connections there are the more chance that will will have noise in our signal. Second is the comfort of the wrist bands, you don't want to be hurting the person that you are measuring. Finally practicality, the wrist bands need to be easy to take on and off, I learnt this by doing prototypes first.
Remember this is just a guide for what I did in 3 weeks and by no means is this the best way to do it or even the best parts that you can use but I decided to put this up because when I started I couldn't find anything like this online.
NOTE: THE BOARD THAT WE ARE PLUGGING OURSELVES INTO ISOLATES US FROM THE MAINS POWER SUPPLY, YOU SHOULD ALWAYS BE CAREFUL WHENEVER YOU ARE USING ELECTRONIC EQUIPMENT.
Step 1: Materials
When I went out to buy parts I didn't really know what I was looking for so I usually over bought materials. This doesn't bother me because I'll end up using this stuff later on but you might want to take this into consideration when you are in the planning stages.
So first was the material for the wrist band. I went to Spotlight, this is a fabric/arts and crafts store for those who don't know it. I got 2 meters of black woven band as you'll see in picture later and 2 meters of velcro that matched the width of the band. I also got 4 D buckles, thread and sewing needles.
Then off to Jaycar (local electronics store) I got 3 meters of coaxial cable with a solid copper core, heat shrink, resin solder, and gold coated quick terminals.
Step 2: Preparing the Cables
Strip the insulation at both ends of the cable, the 2 photos of the end of the cables show how it should look like.
On the end that we are going to put into the quick terminal I then put heat shrink over the end to make sure that none of the outer wire will touch the copper wire or terminal (this is important because in the board that we feed the signal into the outer wire will connect to ground).
On the cable that goes to the leg I also put heat shrink on the other end just because it only goes to ground.
Next is the soldering. Feed the copper wire through the bottom of the quick terminal and crimp the terminal onto the cable as much as possible. Take your iron and resin solder and heat both the wire and the terminal and allow the solder to flow onto it which should create a nice connection like the one in the image.
Step 3: Preparing the Bands
Next I sewed on the D buckle, simply feed the band through and fold back over. I used safety pins to hold it in place while I started sewing.
Not too sure what the stitches are called but I did 3 rows to secure it. First a looping stitch over the end, then a cross stitch in the middle and finally a running stitch near the D buckle.
In the image below you can't really see the first line of stitch that I did.
Step 4: Connecting the Components
In my opinion this was the hardest part to do, figuring out a way to attach the cable to the band in a way that when the band was put on the quick terminal would have good contact with the persons skin.
In the picture you can see the way I did it, I cut a small slit in the band with a stanley knife and pushed the terminal through. To connect the quick terminal to the band I first tried some 4 minute quick hardening clear epoxy. It didn't work took forever to dry and I eventually wiped most of it off and when it had dried I sand papered the rest off. I ended up using 3 minute superglue and this worked really well.
The little bit of band below the terminal I also superglued to the cable.
Step 5: Adding the Velcro
The last part of this project is sewing on the velcro. As you can see in the image it covers where we inserted the cable over the band and makes it look a bit tidier.
The main part of this is just making sure you have enough velcro on each side so that when it goes around your wrist it'll line up, that's not that hard just try it on yourself and measure it out before sewing anything on.
After this your done, congratulations you're now the proud owner of ECG electrodes.