Four separate pressure sensors not only give feedback about where I'm pressing, but also how hard. The sensitivity is ideal for finger pressure. Though it is not linear, it is stable. Very sensitive to light touch and then it takes a lot of pressure to reach the minimum resistance.
The inside looks just like the fabric pressure sensors, except each stitch is connected to a separate conductive fabric tab. The downside is that separate tabs and connections to these tabs take up a lot of space, especially if you want to achieve a tight matrix of sensors. A grid of lines and columns and some code to analyze these (separately power and measure) would allow for much tighter spacing. This version is nice because it is so simple.
To make the sensor fully fabric one can use EeonTex conductive textile (www.eeonyx.com) instead of the plastic Velostat. Eeonyx normally only manufacture and sells its coated fabrics in minimum amounts of 100yds, but 7x10 inch (17.8x25.4 cm) samples are available free of charge and larger samples of 1 to 5 yards for a minimum fee per yard.VideoVideo
This Instructable covers two slightly different versions of the pressure sensor matrix. The only difference being the spacing of the individual pressure sensors in the matrix. In one of them they are placed practically next to each other (white) and in the other there is a 1cm space in between each sensor (purple), but because of the thickness of the neoprene it is not possible to press in between the sensors without pressuring a sensor. Hope this makes sense.I am also selling these handmade Thread Pressure Sensors via Etsy. Although it is much cheaper to make your own, purchasing one will help me support my prototyping and development costs >>http://www.etsy.com/shop.php?user_id=5178109
The materials used for the sensor are basically cheap and off-the-shelf. There are other places that sell conductive fabrics and Velostat, but LessEMF is a convenient option for both, especially for shipping within North America.
Velostat is the brand name for the plastic bags in which sensitive electronic components are packaged in. Also called anti-static, ex-static, carbon based plastic bags... you can also cut up one of these black plastic bags if you have one at hand. But caution! Not all of them work!
To make the sensor fully fabric one can use EeonTex conductive textile (www.eeonyx.com) instead of the plastic Velostat, but at the moment EeonTex conductive textile is only available in a minimum of 100yds. But try ordering samples!
I chose to work with neoprene because it offers a form of natural force-feedback and also it is great for sewing into with the conductive thread and thus isolating it. But you can easily replace the neoprene for some regular stretch or non-stretch fabric and even try felt or kind of rubber.