Skin electronics

Exploring skin electronics

For this week assigment, we had to explore the possibilty of integrating intelligent circuitry directly onto the human skin. I can definitively see skin electronics as a research field that could help enhance the human body even more by making it able to interact with outside object such as your telecommunication and IOT device. One particular research that I find amazing was driven by MIT researchers, I absolutely love the mix behind art and technological innovation.

For my week project, I will try to create a process where you can easily and cheaply reproduce this kind of "tatoos".

Safety measure and designing the circuit.

My prototype will consist of an array of six LED, since I will be putting this directly onto my skin, I need to make sure that the circuit will represent no harm. Here, we can find some very important information about the human resistance, in particular it's skin resistance.

I did the test and using a multimeter tried to measure the resistance of my skin while being dry and then while being wet, the difference was pretty drastic, the resistance drop by a huge factor while having a wet skin, but even then, the resistance is more than enouph to cancel the kind of current that I want to use for my circuit.

While dry, my skin resistance was approximatively 1.5M omhs, while wet, it was down at 200k omhs.

I did two iteration of my circuit, one in series and the other one in parallel. Let's assume that each of my LED needs a forward voltage of 3V to work correctly and they will each draw 30 mA. In series, you will then need 18V (3*6 Led) to supply correctly your leds, while in parallel you would only need 3V, but you will then draw constantly 180mA. If I understand correctly, the later exemple would be more "dangerous" since more current could potentially be able to flow trough your body, but at such a low voltage, the pressure would not be sufficient to cause harm.

For both case there is still an issue tough. First of all the Arduino Uno wich is the microcontroller that I was planning to use for my circuit is not able to output more than 5V on it's digital pin. That means that I will absolutely have to use an external power supply and a transistor for my in series circuit (since I would need 18V to power all of the LEDS). Ok that one things, another issue now, In parallel, even tough I would be ok to use a digital pin to supply enouph voltage into my LEDS (3V), I still have an issue because each arduino pin is made for a maximum current of 40mA passing trough them. That means that either way, I would have to use an external power supply. Damn. A 3V coin battery should technically do the trick for my parallel circuit so that is not so bad but still important to consider.

Making the printed circuit board

The thinnest conductive material I had here at the lab were conductive silver sheets. These silver sheets are very light and are less than 0.08mm thick. The first thing I did was to test if it was easily cutable on the vinyl cutter, I used the cricut maker with the settings of silk material to try it out.

Next thing was to "draw" the circuit, to do so I used inkscape to generate some very basic shape, one shape for my in series circuit and another on for my parallel one.

After cutting these shapes, I encoutered my first issue, I can't directly solder onto my fabric, the heat instantly melts my silver fabric. So I decided to use copper tape and create solder pads with it. The final circuit looks like this:

It may not be super clean, but I still find it cool, now let's try to hook it up to power to see if it works!

It works perfectly!, The next step is to bring it onto the skin, to do so I used transparent double sided tape and tape it to my arm, the result were pretty cool, could be better, it does not looks nor feel like a "tatoo" but it's a great start for sure!

I then used a transistor and an arduino to run a simple blink program. I also had the idea to stick the circuits to a very thin PETG sheets so that I could create flexible circuit for demonstration here at the lab.

here is the very basic code for blinking my circuit:

You can find the files for this week assigment here