Textile Multitouchpad

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About: ... using laser cutter, PCBs, 3D-Printer and whatever i get into my hands to build things

For detecting contact pressure areas for one part of the Personal Photonics project of the Media Computing Group Aachen, funded by the German Ministry of Education and Science, we developed a textile Multitouch input device, reusing parts of successopr projects like Intuitex and Pinstripe. The idea was embroider a pad area structure with conductive silver yarn on a textile and covering it with one layer of EEontechs piezoresistive fabric as well as a sheet of conductive fabric on top. Using a bunch of MSP430 controllers for analog sensing, each pad works as a pressure sensor.

Step 1: Textile Part

For the textile part we emproidered the hexagonal structure on a textile, with wires to a centralised connector area. These wires are covered in a second step with black, nonconductive Yarn to prevent short circuits in this area. Them we applied first a thin (nonconductive) mesh as distance holder, afterwards one layer of Eeontech piezoresistive fabric and finally the conducive fabric. The latter is connected with one pad below with conductive thread, otherwise the sandwhich structure is sewn together with non-condactive yarn (just make sure to not sewn trough the pads).

Step 2: Electronics

For interconnection with the controller board a small PCB for 4 microcontroller is milled, which is pressed against the textiles pads with a 3D-printed Clipper from behind. For testing, additional a breadboard version was made (a little bit clumsy for beeing really wearable).

Step 3: Programming and Testing

The Programming part was made with an MSP430 launchpad, which also served later as bridge to the computer. Each of the four controller of the board was programmed seperate, basically checking each anlaog value on after another via serial communication. The result is then displayed with Processing on the Screen.

(Fun stuff was then using an old Reprap printer as testing workbench if the system runs reliable :)

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