New Textiles 2012

A glove that can be programmed to respond differently to touch can be wonderful for games. If you have ever played the game “Red Light, Green Light” you’ll know that having something visual during the game play can help the process go smoother and add another element of fun and creativity to the game. Similarly, a game of tag can also be played in the dark if the person who is “it” has a glove that responds to touch by lighting up when he catches someone. As I began on this road of thinking, I really wanted to make an easily wearable pressure sensor to control LEDs, and then incorporate the product into a traditional game with a new twist.

The materials I had access to were velostat, felt, conductive material, conductive thread, 5 LEDs, snaps, the sewing machine, and the Lilypad Arduino. The main idea I had is that I wanted the glove I am making to respond to touch, which can be achieved by making a resistive sensor that decreases its resistance if pressure is applied to it. I experimented with using velostat to make a resistive sensor. I searched online for previous work on these kind of resistive sensors and came across one on Instructables by Plusea. I read through the method and used it as sort of a guide in creating my own.

step 1: Cut four pieces of felt into small, button-like shapes. I cut four pieces even though two will achieve the goal because I want the button to have a rather thick texture so it feels nice.

step 2: Cut four pieces of velostat into circles. I know that I may not use all four, because if I put too much velostat in the sensor, that means it will have a higher resistance. The internal pull up resistor in the Lilypad is ~35k and I need the sensor to have resistance on the same magnitude as the internal resistor in its inactivated state for the pressure sensor to work nicely.

step 3: Next I double threaded the needle to sew a simple pattern onto one of the felt pieces. Notice I sewed a piece of conductive fabric to the end of the felt pieces. This is to make it so that I can connect other pieces of the circuit to the sensor easily. I double threaded the needle because it allows more current to travel through, which gave me a small control over the resistance of the thread. It also allows me to make the sensor more responsive to pressure. I did the same for the other side of the felt piece.

step 4:  The two felt pieces come together, sandwiching the conductive thread in between. I placed an extra felt piece on either side of the sensor to 1) hid the conductive thread and 2) create a nicer, thicker texture for the sensor.

step 5: Now is the time to play around with how much velostat to put into the sensor. As mentioned earlier, I wanted to create a sensor which has a resistance on the same magnitude as the internal pull-up resistor in deactivated state. As for my sensor, I still wasn’t sure how many pieces to put in at this point, so I just moved onto the next part for now.

step 6: Making the glove is very tricky. As I’ve never sewn before, I viewed this as a fun challenge. I traced a pattern around my hand and cut out the shape on felt. The first three iterations did not work well because, as a common mistake, I cut the pieces too small and neglected to account for the third dimension of my hand. However, the fourth iteration was successful and I sewed it up with the sewing machine.

step 7: In order to attach and detach the Arduino to my glove, I soldered buttons to the Lilypad and pressed buttons into a piece of felt so that I can button the Arduino on to the glove.

step 8: It takes a little effort in mapping out the exact route of the circuit on the glove so that 1) the wires don’t cross, 2) the glove looks aesthetically pleasing, and 3) the circuit functions correctly. This is the design I came up with for the back of the glove. The palm of the glove is simpler than the front: the A5 pin simply go to one side of the sensor and ground goes to the other side of the sensor. All the LEDs are connect to ground on the palm of the glove in a similar “whirlwind” pattern of the front of the glove. All the stitches are done with conductive thread, double threaded to decrease their resistance.

[palm  +  back of the glove]

The physical assembly is now almost complete with the exception of how much velostat to put in the sensor. I used the serial monitor on the Arduino to aid me in calibrating the sensor. After writing some simple code and turning on the serial monitor, I discovered that putting three pieces of velostat in between the felt allows me the best range in voltage drop over the sensor as a pressure sensor.

Resistance | Calculated Voltage across sensor |Measured Voltage Drop across sensor

400kΩ       |                       3.4V                                    |                          3.4V                                      |                  inactive

1kΩ             |                     0.12V                                   |                       0.2 V                                        |                active

Now that the physical assembly of the glove is finished, the software portion of the project begins. I wrote a couple of behaviors for the glove to make it interesting. These behaviors can be seen in this video.

behavior 1:  When the glove is not squeezed, the LEDs on the thumb, middle and pinky fingers light up. When it is squeezed, the LEDs on the forefinger and the ring finger lights up instead.

behavior 2: This is a visualization of how hard the glove is being squeezed. The LEDs turn off in a linear relationship with how hard you are squeezing or pressing the glove.

behavior 3: This pattern can be used in a game of roulette or a game of “red light/green light.” (Except the title will be modified to “light on/light off” of course.)