I always try to use what I have on-hand for any project, and I already had the yarn, doll, paint and spray adhesive, but here is a complete materials list:
*small cardboard box
*velcro circles
*yarn, thick string, ribbon or elastic
*hot glue gun, or industrial adhesive.
*paint (I used spray paint)
*spray adhesive, glue, or mod podge
*doll
*awl or other object for poking holes in the box like a phillips head screwdriver
*box cutter or exacto knife
*scissors
*printer (or you could draw the EKG read) and paper
My daughter already had this plastic baby doll that we found on Amazon. Pretty much any doll will work as long as the shirt can come off. I found a small cardboard box at the craft store for about $3 and spray painted it off-white with a can I had in my garage. You can use any color but whites, creams and grays will seem the most realistic.
The velcro circles come with "male" and "female" sides, so to speak. I used my hot glue gun to glue the rough ones to the doll's chest. (I found that the hot glue didn't do the best job. We have to be careful when removing the EKG "electrodes" from baby's chest because these circles seem like they want to come off, in retrospect, I would have used an industrial adhesive, but we make it work.) Also, if you have a cloth doll, these circles can be sewn on or hot glued. I then took three, 20-inch lengths of yarn (you could also use very thick string, cord, elastic, ribbon, etc), knotted the ends, and glued each of those to the back of the softer velcro circles.
The next step was to make three small holes in the side of the box to thread the other ends of the yarn through. I used an awl, but a phillips-head screwdriver would also work. You want the wholes to be small enough that the yarn is a tight fit. I also used the awl to poke the yarn through my holes while pulling through on the other side.
On the inside of the box, I tied the yarn in a few knots, and then added a bit of hot glue and pulled the yarn snug from the other side to adhere the knots to the inside wall.
Next I went online and did an image search for "EKG monitor" and "EKG read" and printed the images for the front of the machine, and for the read that would come out. You could also draw these things on paper as well; This is all for pretend so it doesn't have to be perfect. I used spray adhesive to apply my monitor image to the back of the box. The reason I didn't put it on the lid is because I wanted to be able to open the back of the "machine" to feed the paper into (you'll see what I mean in a bit.)
Right below the monitor display, I used a box cutter to cut a slot that runs most of the way across the front of my EKG machine. I went back with my scissors and just worked the slot back and forth, rocking the scissors around, to widen the slot a bit for my paper.
Now I am able to feed my EKG read paper through the back, and it will come out of the front just like a real EKG machine does when it provides the print out of the heart waves.
For storage and travel, the read paper and the electrodes can be tucked inside the box, and the lid can be placed on.
Your toy EKG machine and doll are complete! I've been using this with my daughter and she loves it. We use her toy stethoscope to check the baby's heart and then I say, "I hear something unusual. Let's hook her up to the EKG machine to get a better look." We apply the electrodes to the baby's chest and help the baby to lie still quietly while the machine prints her heartbeat. Then we pull the paper out of the slot and review the results. Sometimes my daughter pretends to wear the electrodes, or put them on me, and we get a readout for our hearts as well. Really, you could make this without gluing velcro to a doll, or without a doll at all by just laying the electrodes connected to the machine onto any toy or person's chest and pretending.
You could really make this with any box you have available. The size and color is totally up to your discretion, and you don't even have to include a doll if you don't want to-The machine itself is a great stand-alone toy on it's own. You could take a simple box, draw a display, draw a print out paper and cut a slot in the box for it to go through. Attach three strings to the box and some kind of circles on the ends (velcro, felt, fabric, bottle caps, whatever) and you'll have a cool doctor toy. There are lots of ways you could make something similar, and for little or no money.