What is this project?
This project is a shirt that has a color changing design. Specifically a design that can change color when given user input. The shirt consists of 6 “pixels” or regions that can change the color of with the use of a phone. The phone connects to a Bluetooth module sewn into the back of the shirt. This Bluetooth module communicates with a micro controller (Circuit Playground Express). This micro controller sends a signal to a MOSFET (60v 30A MAX), a electronically controlled switch, the MOSFET allows power to flow through the heating pads placed on the underside of shirt. The thermochromic ink screenprinted on the front then reacts to the heat from the heating pads and changes color.
How I feel about the project?
I’d say while it isn’t polished enough to be a product, I think that it shows a proof of concept really well. So overall I’m happy with it for what it is. One thing that bugs me is that the wires and electronics weigh the shirt down in certain areas. As well as, the heating pads underneath the shirt are kind of bulky.
How does it stack up to my original idea?
I was a bit too ambitious as initially I wanted to have somewhere around 30+ individually changeable regions. However my goal of having a “non-obvious” design changing shirt was a success. In the very early stages I wanted to use fiber optic cables and diffuse the light, but I think using thermochromic ink is much better and has a much greater effect.
Largest Project Hurdles
Power distribution was probably the biggest problem I had with this project. Ultimately I decided to demo this shirt using a wall plugin, as it would need a sizable lithium-ion battery to be able to supply the current the heating pads needed. The wires underneath the shirt are also something that was difficult. Many of the sources I checked online said that the heating pads wouldn’t work if hooked up with conductive thread instead of hookup wire. This meant I had the run wires around the side of the shirt instead of sewing into the shirt. I think conductive thread is doable but not with these heating pads. Also when I made the final power distribution board (see below) I had to go back and rewire a few times.
If I had more time
I plan on updating this project in the future. Hopefully make the electronics smaller and the wiring underneath more neat. But I think the next big step I’d like to take would be to use conductive thread as both the wiring to the power supply but also to make my own heating pads. I think the large current draw, bulky pads, and less than neat wiring underneath all be solved by finding the right kind of conductive thread. I could make smaller pads that were embedded in the shirt as part of the fabric instead of the plastic wrap feeling and larges ones I’m using now. The use of less power and less space on the shirt also means I could fit heating pads into the design area as I originally wanted.
The Final Product
Above is the shirt working. It takes a while for the pads to heat up the entire section the outside edge is the last to change. It takes about 10-15 seconds for the section to change color after receiving input from the app. It then takes 1-2 minutes to cool down and go back to the dark green color.
Here is the app that sends commands to the shirt, nRF ToolBox. The app communicates with the shirt via Bluetooth Low Energy. But buttons label 1 though 6 are for the panels on the shirt (i.e. top left button toggles top left triangle section on and off). In the bottom right is a reset button. This turns all the panels off.
The last thing I added to the shirt was the power distribution board. This board has all the connections to the MOSFETS, heating pads, and the power plug. Connections to the MOSFETs include both ends of the heating pads ground wire and the output pins on the Circuit Playground express (blue wire). The MOSFET acts as a digital switch closing the circuit when the gate pin on the MOSTGET has a positive 5v.
Here is the interior of the shirt. That orange and gray envelope was made because the transistors were getting a lot hotter than I expected. wire routing was done with safety pins. While there is a lot of excess wire I wanted to make sure I had enough slack. I had needed to rewire this a few times for either bad connections or not having enough slack. Once I got it to a place where it worked and had enough slack to wear I let it be.
This is the poster I had during the presentation. I also had the shirt on a mannequin to live demo it at the student fashion show.