Therma Pattern
Therma Pattern allows the user to choose different patterns to display on their shirt.
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One day our clothing will display information and allow us to interact with it. Providing more variety to what our apparel can do and thus limiting the need for excess garments and additional smart devices. Therma Pattern begins this exploration by creating a flexible material that can change visual displays.
The Therma Pattern shirt has 21 woven nitinol structures painted over with thermochromic pigment to control the color change. Nitinol is an excellent actuator for quickly heating thermochromic pigments. Three layers of the garment were made; one Ponte knit and two silk organzas, to isolated layers. Similar to PCBs, each layer of fabric acts as an insulator preventing current flow.
Current heats up nitinol, which changes the color of the thermochromic pigments. The more current sent to the Nitinol, the hotter it gets, changing the thermochromatic pigments faster. Through many tests, nitinol was preferred over the conductive thread to create a change in thermochromic pigments. By weaving nitinol together into an efficient structure, the thermochromic pigments changed colors more rapidly. Two half drivers (NCV7719) were used to control the current flow going to each woven nitinol structure. A Teensy 3.2 was used for the microcontroller of the project. A Micro Oled was attached to assist the viewer in picking a pattern displayed on the garment.
Music by Jon Hopkins - Candles
Nitinol Tests
Two-ply Conductive thread and 0.005" Nitinol were woven into a Ponte knit and then painted with thermochromic pigments. Many tests were run on the two materials to compare the speed of color change vs. vibrancy.
.0.005" Nitinol was chosen after examining Flexinol's technical datasheet. A diameter too small will have too much resistance per inch, while a diameter too big will require too much current to heat up. Looking at the technical datasheet, one can see that to send about 250mA will reach roughly 194°F. Since the thermochromic pigment needs to be heated above 88°F, one could estimate that 100mA is required.
After extensive testing, it was concluded that Nitinol will create a faster and smoother color transition than conductive thread because it heats faster due to its nickel-titanium composition.
Figure: two graphs, one comparing Voltage vs. Current, the other comparing transition times of the two materials. Note: the lower the current, the less vibrant the color change was. (A) plot comparing Nitinol and conductive thread to see how much voltage was needed for certain currents. (B) plot comparing Nitinol and conductive thread to see which changes color faster.
Video: Nitinol woven to 1.1cm long vs Conductive thread woven to 1.1cm long in ponte knit
Hardware Block Diagram
Software Diagram
The code to control the Therma Pattern shirt operates with a finite state machine. An image of how the finite state machine works is shown to the left. Link to the code
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