LED Pressure Matrix

By Linh My Truong

I experimented with LEDs, fabric printed with thermochromic ink, a heating pad, and a Loomia Mini Soft Pressure Matrix to create a swatch I call Eye in the Sky.

Since the pressure matrix has nine possible points, I used eight LEDs and reserved the bottom left point to trigger the heating pad to turn on. I used an Arduino Uno for my microcontroller to accommodate all the actuators and pressure matrix sensor. I am hard-pressed to remember the last time I used so many pins! In order to hook up the pressure matrix, I referenced the Loomia datasheet. I connected the heating pad to a MOSFET to trigger it with my microcontroller and a 5V battery pack to give it enough power and current (the 5V output on the Arduino Uno maxes out around 400-500ma).

I found a marbled fabric sample I made ages ago and an eye I screen printed with thermochromic pigmented ink at ETC. I hand embroidered the eye to the fabric, but this inadvertently caused the eye to be slightly raised from the rest of the swatch. The heating pad heated up quickly, though, and I did not notice a considerable lag in the color change from purple to pink even with the slight gap between fabric and heating pad.

For the Arduino code, I referenced the Squishy Circuits project by Lee Wilkins and the pressure sensor matrix by KOBAKANT. I modified the code so that it would trigger multiple points simultaneously, which was fun to play around with my thumb.