making stuff out of things.
It’s been a short while since we last posted, and we thought it might be time to update you on the progress of our mUUshi gestural sensing surface.
We have been doing several tests to refine our design, making it faster, more sensitive, and a little more machine-washable. The surface is almost complete, and will be getting mounted to a beautiful walnut case later this months.
Also, we have just sent our eagle board design to get printed, and hope to receive these in the next couple of weeks. There is a picture attached of the eagle sketch, and we’ll be uploading a few new pictures of the surface friday afternoon.
Also also, something to look forward too…we have been working hard to finish off a demo video for mUUshi, giving you a better feel of what a gestural sensing surface really is, and how a fabric touch surface can be used to create sound and visuals.
ilyfa…because sometimes different is better.
After a huge set back with our first sensor build, we finally have a fully functional second sensor.
Unfortunately, the first sensor we built had some significant design flaws when it came to attaching the conductive thread to our Teensy board. With lessons learned, we soldered on.
Marked differences with the new sensors are, firstly the inclusion of EeonTex Piezo-resistive fabric - which increases the durability of our sensor by making it 99.9% fabric, with the exception of the snaps on the side, and PCB at the bottom where the wires connect.
Another point to note, is we decided to go with a technique used by which you sew your conductive thread traces to a dot matrix PCB which connects to your board. This is then hot glued down for extra durability. One point to note is that, the hot glue has disrupted the connection in one of our traces, and has resulted in the resistance in this traces tripling, making it difficult to get a responsive reading from it.
Here are some pictures of the second sensor from our flickr. hope you enjoy.
Small update, we received 1.5mm neoprene today, with an amazing neon green nylon fused to one side, with black nylon fused to the back. This neoprene is 0.5mm thinner then our previously used 2mm neoprene.
Our hope is that with the use of a thinner neoprene, we can construct a more durable and sensitive sensor surface by layering multiple sensor arrays, with each different layer corresponding to the different functions of the sensor.
We would like individual layers sensing each require parameter, one for X and Y position sensing, and another separate layer tending to our Z, pressure, reading.
We are in the process of building a pressure mapping application, either in PD, or MatLab which we will post on the wiki as soon as it’s completed. We will also give you some cool graphs and charts to show you what kind of read data we are getting so far from the sensor.
ilyfa…because sometimes different is better.
We have been using the piezoresistive material Linqstat while prototyping our gestural sensor. Linqstat is sold by a company in Canada call Caplinq, and is similar to 3M’s Velostat. Commonly used to make antistatic bags, both Linqstat and Velostat are thin piezoresistive films.
The piezoresistive effect describes change in the electrical resistivity of a semiconductor when mechanical stress is applied.
While using Linqstat, we have made some interesting findings that we would like to share with you.
***NOTE: we have not used Velostat, but it can be inferred that because these materials are very similar these rules could apply to both***
Sewing with conductive thread is much like sewing with normal thread, with your different types, sizes, and strengths for different purposes. For our project we wanted a thread that was easily machine sewable, but still has the strength to hold up when subject to repetitive strain. [pullquote]Neoprene comes in several different varieties, from basic uncoated neoprene, all the way to perforated neoprene, commonly used for medical applications.[/pullquote] An amazing help in our search for a thread to suit our purposes was Fashioning Tech’s Conductive Thread Overview, by Syuzi Pakhchyan. In her overview, Syuzi reviews several different threads available on the market, giving detailed descriptions of there possible uses, resistance, thread weight, and where they can be purchased. After picking out our thread (we went with the Silver Plated Nylon 117/12 x 2ply thread, available from SparkFun) we went about testing how it sewed on our machine and made a few notes we would like to share with you. As we were sewing onto a 3mm neoprene, we required some specific parts to accomplish such a task.
Neoprene comes in several different varieties, from basic uncoated neoprene, all the way to perforated neoprene, commonly used for medical applications. The neoprene we are using has nylon fused to both sides of the material. The nylon coating is thin, and makes the material a little more friendly for touch applications. We chose to sew a zig-zag stitch onto out neoprene (see image), which can be accomplished using a standard sewing machine (preferably a metal machine, as the extra weight helps when sewing with thicker materials), and a stretch or ballpoint needle. The needle is of great importance as if a standard universal needle is used the conductive thread may fray. Also stretch and ballpoint needles are specifically designed for sewing with stretch materials like neoprene. Another thing to note is that our machine has a top-loading bobbin, opposed to a side-loading bobbin. Although both will sew in the manner needed (a zig-zag stitch with conductive thread onto neoprene) the top-loading bobbin is a better choice, as the thread traces will be tighter to the surface of the neoprene, ensuring the thread does not come loose during use. We also observed that when sewing conductive thread onto neoprene, we had to pre-start the stitch before the machine could be engaged. When we engaged the machine right away, we noticed the frustrating problem of having our first few stitches skip, making for an inconsistant traces. (note: this may not occur on all machines, also there is the unfortunate trade off of the first few stitches being loose, however, this method lends itself to having enough material to later attached the conductive thread to a PCB-Dot Matrix stripboard) For testing purposes and quick retooling we used small eyelets to connect out conductive thread to wire. Using small eyelets also eliminates the need to solder wires (although soldering parts together does make it easier to test). Using the eyelets is unfortunately a temporary option, and an alternative method may want to be found to allow the sensor to be used in more practical applications.