Stitching conductive thread into neoprene to create a pressure sensitive pad. This sensor is very similar to the Fabric Bend Sensor
or vis-versa. And also close to the Fabric Pressure Sensor
, but the difference is that the conductive surface is minimized by stitching only a few stitches on either side with conductive thread. This creates a good fingertip pressure range.
The resistance range of these pressure sensors depends a lot on the initial pressure. Ideally you have above 2M ohm resistance between both contacts when the sensor is lying flat. But this can vary, depending on how the sensor is sewn and how big the overlap of the adjacent conductive surfaces are. This is why i choose to sew the contacts as diagonal stitches of conductive thread - to minimize the overlap of conductive surface. But only the slightest touch of the finger will generally bring the resistance down to a few Kilo ohm and, when fully pressured, it goes down to about 200 ohm. The sensor still detects a difference, right down to about as hard as you can press with your fingers. The range is non-linear and gets smaller as the resistance decreases.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
As in all my Instructables 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. But they also ship to Europe within about 10 days.
Velostat is the brand name for the plastic bags in which sensitive electronic components come packaged in. Also called anti-static, ex-static, carbon infused plastic (So you can also cut up one of these black plastic bags if you have one at hand. But caution! Not all of them work, so test them first!)
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.