week 5 - E-Textiles and wearables I
Introduction to electronics in textiles. Techniques of making soft/fexible circuits in fabrics. Introduction of the microcontroller concept.
Create a fabric sensor. Then create fabric circuit using one or more techniques covered in the course.
To begin understanding the electronics in fabrics we first experimented building a simple circuit to lit a LED sewing it by hand with a conductive thread. We build a very simple pressure sensor to be used as switch to turn the LED on and off.
We cut a very thick felt with a hole in the middle and added on each side a conductive textile layer to create the switch. Then we created a battery pocket sewing an extra piece of textile with non-conductive thread, making sure to separate the positive and negative poles. With the conductive thread we sewed the cicuit and added the LED (positive leg - longer one - to positive side of the battery and negative leg to negative side of the battery) tightening well the thread to the LED legs to make a good connection.
We also experimented building and analog pressure sensor with flexible semi-conductive material in the middle of two metalic layers. We connected each metalic layer to a crocodile clip and the to the arduino to read the values. To stabilize the values which were floating we added a push-up resistor.
fig 5.1 - Simple circuit with pressure sensor and one LED.
Since we were close to halloween during this assignment, my goal was to develop a costume that I could wear in the halloween night. I decided to make a lightning hear with red LEDs in a black t-shirt that would lit with a pressure fabric button.
fig 5.2 - Analog pressure sensor with flexible material.
Building the circuit - first attempt
First I drew the circuit in Illustrator to understand how would it work and where should each component be placed. I used as reference the parallel circuit shown in fig 5.3.
After drawing the circuit I proceeded to create an efficient battery pocket, since on the experiment the connection of the battery was not good with only the thread. For this reason I added inside the pocket "walls" a squishy foam which would help pressing the conductive textile against the battery.
Next I placed the LEDs in the t-shirt. I didn't want the legs to be showing so I crossed them to the inner side of the t-shirt and bent the legs.
fig 5.3 - Scheme of the parallel circuit taken as reference.
fig 5.4 - Heart circuit drawn in Illustrator.
fig 5.5 - Making the battery pocket.
fig 5.6 - Parts of the battery pocket.
fig 5.7 - Placing the LEDs.
fig 5.8 - LEDs' legs bent in the inner side.
After sewing by hand the connections with the conduct thread to the first LED I tested if it was working and unfortunately it wasn't. I noticed that was a interuption of the connectivity close to the battery pocket. That happened because the conductive thread is very delicate and it breaks and entangles very easily while sewing. It broke once and I though I could rebuild the connection by starting again on top of the broken end but that didn't happened so I had to undo everything and start again. I sewed the connections until the first LED again and realized that my circuit was wrong and only one LED would lit. Furthermore it would be constantly lit and the pressure button would not work.
Building the circuit - second attempt
I redraw the circuit and decided to move the pressure button to stay in connection to the battery pocket. Because of the problems I had sewing the circuit by hand I also decided to use now the embroidery machine.
Since I had made some hole in the old t-shirt to place the LEDs, the textile became a little fragile. To start fresh I bought a new t-shirt that had a stronger textile.
To use the embroidery machine, I exported the file as WMF. Using the PE Design software, the drawing is converted to stiches. It is necessary to separate the drawing in different color. Each color should represent a different thread to be set in the machine and not the color of the thread meant to be used. The file then is saved in PES format and saved in an USB stick to be inserted in the embroidery machine.
Next I prepared the t-shirt by pasting paper on the back to streighten the material and positioned the frames of the machine in the center of where my drawing needs to be on the t-shirt.
With the help of Adriana, I inserted the drawing in the machine, placed the frame and the thread.
After having the circuit embroidered, I proceeded to continue the part of the circuit that would connect to the battery pocket located on the ribs. I decided to sew it in the sewing machine because this part would not fit the embroidery machine frame.
The conductive thread is very difficult to use for it's texture is not smooth and it doesn't flow very well in the machine. I had to sew it very slowly and carefully and did several tests before starting sewing on the t-shirt. With a lot of difficulty I managed to finish the circuit and added a pad of conductive textile with foam inside to increase the area in contact with the battery. I tested it with the multimeter and afterwards with and LED and a 3V battery, which fortunately worked well. For the button I recovered the one I had made previously for the first t-shirt, which is a "sandwich" of two conductive textiles and a foam with a hole in the middle. When pressing the button, the conductive textiles would touch each other and close the circuit.
fig 5.13 - Connectivity test
fig 5.14 - Pressure button and battery pad.
fig 5.9 - Fail - Only one LED lighting up.
fig 5.10 - Drawing turned to stiched in PE Design software.
fig 5.11 - Inserting the T-shirt in the frame of the embroidery machine.
fig 5.12 - Heart circuit being sewed by the embroidery machine .
Next I fixed all the LEDs, crossing the legs throught the fabric to the inner side of the t-shirt. Since the embroidered circuit was really thick, I used a thick needle to open a hole fron inside the t-shirt and removed while pushing the correct LED leg inside, as suggested by Wei Cheung, which was very successful. Once I crossed the legs, I twisted them inside as before, shown in fig 5.8. The enbroidered threads were so close to one another that only sticking the LEDs through it had enough connection and I didn't have to sew them.
I sewed the button connecting the outer connective textile to the negative line and tested it with the battery. I tested it and the light was flickering. The problem was that the inner conductive textile of the button was touching the thread connected to the negative side of the battery, closing the circuit. I then removed the inner conductive textile of button (fig5.16) and it worked but still very poorly. Esin, our Fabricademy colleage, suggested to add another battery and that solved the problem: all LEDs were lighting perfectly. To improve the aesthetic I sewed the pocket with a back fabric and drew with red thread a power button icon on it.