Previous Instructable >> Fabric Bend Sensor
Using neoprene, Velostat, conductive thread and stretch conductive fabric to sew your own fabric bend sensor. The sensor actually reacts (decreases in resistance) to pressure, not specifically to bend. But because it is sandwiched between two layers of neoprene, pressure is exerted while bending. Allowing one to measure bend (angle) via pressure.
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.
To prove the competitiveness of this sensor vs. a commercial bend sensor I made a short video in which Sheep demonstrates their similarities.
Step 1: Materials and Tools
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. Also called anti-static, ex-static, carbon based plastic& (So you can also cut up one of these black plastic bags. But caution! Not all of them work!)
- Neoprene 1.5 mm thick HS quality from www.sedochemicals.com
- Velostat by 3M from http://www.lessemf.com/plastic.html
- Conductive thread from http://www.lessemf.com/fabric.html
- Stretch conductive fabric from http://www.lessemf.com/fabric.html
- Fusible interfacing from local fabric store
- Regular sewing thread from local fabric store
- Pen and paper
- Fabric scissors
- Sewing needle
- Possibly pliers for pulling needle through neoprene
Step 2: Stencil
Print out a copy of the Neoprene Bend Sensor Improved PDF and cut out the stencils for the neoprene, Velostat and stretch conductive fabric tabs. Trace it twice onto your piece of neoprene and cut these out. Now mark the inner stitches and placement of conductive fabric patch onto these cutouts. Caution! The tracing should be identical and NOT mirrored.
Download Stencil PDF >> http://kobakant.at/downloads/stencils/neoprene-BS-improved.pdf
Step 3: Ironing
If you have not already fused interfacing to one side of your stretch conductive fabric, then youll want to do that now.
Now place the two pieces on top of the neoprene cutouts and fuse these together with an iron.
Step 4: Sewing
Thread a needle with about 50 cm of conductive thread (do not take it double) and stitch from the side into the first marked stitch hole and then make the four stitches and at the end connect to the stretch conductive fabric tab with at least five stitches. Cut the thread and repeat on the second piece of neoprene.
The reason the stitching on both sides must be identical is so that when they lie on top of each other (facing each other) the stitches crisscross and overlap in one point. This has the advantage that the stitches will be sure to cross (make contact at these points) and second that the point of contact is as small as possible. Ive found that if the conductive surfaces are too big that the sensitivity of the sensor is no longer good for what I want.
Step 5: Closing the Sensor
Start sewing around the edges of the two neoprene pieces. Make sure to displace them by the 1.5 cm marked on the stencil. And dont forget to insert the two pieces of Velostat before closing the sensor all the way!!!
You can add more or less pieces of Velostat to control the sensitivity of the sensor.
Step 6: Sheep's Demo
You are finished. To demonstrate that it works simply hook it up to a multimeter and set it to measure resistance (Ohm). Bend or press the sensor and the range should lie between 2K and 200 ohm.
You can also hook it up to your computer and graph the input. For this you will need to follow the instructions in the previous Fabric Bend Sensor Instructable (see step 7) >>
Let me know if you make one, I'd love to see some photos.
kimoakes made it!