Craft: The beating crystal heart or how to become the IronMan of the Middle Ages?

It’s been a few years that I’ve been involved in LARP (Live Action Role Play): a form of role-playing game where participants physically portray their characters (you can think of it as improvisational theater).

As I’m also a crafty person (I’ve always had at least 3 projects ongoing…), it was a matter of time before I decided that I must create my own costume, and use some professional skills to do so.

So here we are: I’m crafting a beating heart in a realistic crystal shape, for a dwarf matriarch war mage — this heart is what makes her immortal.

The aim:

1. It should look like it’s a crystal that is literally inlaid into the chest.
2. The crystal heart should be green.
3. It should blink/beat in sync with a heart rate.

Prerequisites:

For this tutorial, you’ll need some tools:

• an Arduino IDE
• soldering iron + wire
• a 3D printer
• a 3D printer wire
• scissors

In this example, I’ll talk about Adafruit products which are the most optimized, as far as my research goes, to be sewn into clothing without overheating/space problems (and I, surprisingly, don’t want to become a human torch in the middle of a scene).

The material:

• Heartbeat sensor (this educational pack in my case)
• LEDs (Neopixel ring x12 LEDs)
• a motherboard (Gemma M0)
• a portable battery (3xAAA)
• a curtain carnation and the cloth that will hold the crystal

The plan:

The crystal will be incorporated into the costume (so it’s easier to wear, and look like a crystal that is fixed into the chest of the character). The costume will have a hole to let the crystal pass through, we’ll use curtain carnation (gold one, because my character is very fancy).

The crystal should be able to pass through the curtain carnation, so it should have a diameter of 40mm max. We’ll print it with a 3D printer and a transparent green wire.

Then, we will need to assemble the actual beating part of the heart and put it in the crystal.

Last but not least, we need to write the magical formula (a.k.a. the piece of code) that will translate the signal received by the heart-rate sensor, into a blinking action that should look like a heart rate.

Once the crystal is working, we need to fix it into the costume.

And…..that’s it! (You now also know why I did not do a diploma in drawing)

The implementation

Create the crystal

I will use this schema from Thingiverse and use a transparent green and rigid wire. We do the first try, with the schema unchanged, to check the measurement, and verify the machine configuration (240°-260° for the wire). We were lucky, it worked perfectly on the first try.

Now we have this:

It is smaller than what we want, we also need a bigger base that will “fit” in the curtain carnation. So here we go, let’s adapt the 3D schema!
This is the final result :

The bottom is empty, so we can put the Neopixel ring in it, and hopefully also the motherboard and Bluetooth receiver, only the battery would remain outside. We could create a lid to keep it all together.

Write the magic formula

We will use here Arduino IDE, which is recommended by Adafruit and easy to use the needed library (you can take a look at this tutorial specifically made for the Gemma M0 motherboard).

Once all the library and programming tools are installed, the preferences configured, and the correct motherboard referenced, we can start coding.

Let’s start with an easy code (given in the tutorial), to make the LED on the motherboard blink, just to be sure the configuration is working.

Now that we are sure that the configuration is good and working (I had some errors with the PC USB port used by default in the IDE on my side), we can start playing with the LED.

Here is a piece of code that will allow the Neopixel ring to light up with a rainbow loop

Now that we know how to handle our LED (and finished a small victory dance), let’s finish with the most tricky part: the heart-rate sensor.

In my case, I have to set up the PIN linked to my sensor to be able to get the information I want, I will receive the signal as a byte, that tells me when there’s a heartbeat and so when to light the crystal.

After some highly scientific testings on the heart-rhythm change (10 squats did the trick in my case), let’s celebrate :
We now have a beating LED!

Assemble the electronic component

We have to solder the different components as in this schema:

3 links will collect each component to the motherboard:

• the ground
• the power (3.3V)
• the signal

This is what it looks once it’s done:

The autonomy will be about 12 hours with a 3 AAA battery.

Assemble the crystal and the beating LED

Now, for “space” management, we will put all of this in the base of the crystal:

It occurred to us at that point, that we were gonna need a lid, so let’s go:

We have a crystal heart! (Whoop whoop)

Assemble the crystal-heart in the costume

Now, we have to put the curtain carnation on the costume:

• We mark the position with a pen

• Cut the corresponding circle

• Put in place the curtain carnation

And this is the final result :
I’m now ready to fire strike people with a snap of my finger !