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In this lesson we will create a fabric pressure sensor. A pressure sensor is a circuit that can display our orientation by visual representation. Using a metal bead and “hot spots” created by conductive fabric, when the metal bead makes contact with one of the petals the circuit is completed and the LED in that position will turn on. This very simple technique for detecting direction of tilt can be used in many different ways and variations, and this lesson aims to illustrate the basic functionality of the design.
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KEY TERMS
LED: LED stands for light-emitting diode. It is a special type of diode that lights up when electricity passes through it. LEDs are unique because they only work when electricity passes through them in the right way, positive to negative.
Conductive Thread: Conductive thread is a thread that can carry electrical current. Generally there are two types of threads available. One type is coated conductive thread, which is regular thread is that is covered with silver. The second type is plied conductive thread, which is thread made out of silver fibers.
Conductive Fabric: Conductive fabric is a fabric that can carry an electrical current. The fabric can be woven or knit and vary in structure from very fine, see-through mesh to densely woven fabrics.
Resistive Fabric: Resistive fabrics is a fabric that tends to have a high level of resistance across a distance. Resistive fabrics are great for making fabric sensors.
Begin by gathering the necessary material and tools for the lesson. We are going to use two types of conductive fabric, stretchy and non stretch. The non stretch conductive fabric will be used to create the conductive "hot spots" on the front of our tilt sensor. The stretch conductive fabric will be used to create the battery pocket on the back of our sensor.
Cut the desired shapes out of each fabric. Before cutting creating stencils can help with this process. For shapes we have three different types. The first shape is two 4" diameter circles cut out of the base fabric. The next shape is 4 rain drops cut out of the non stretch conductive fabric and the last shape is the batter pocket out of the stretch conductive fabric. The battery pocket resembles a shape of shield. ( Keep in mind you are not limited to the sizes or shapes mentioned above. You can do what you prefer)
The circuit for the tilt sensor is fairly simple but can easily get confusing. There are two parts, the front and the back. The front of the circuit consist of of the metal bead and conductive hot spots and the back is where battery pocket and majority of the conductive thread are. In case you every get lost refer to this diagram for help.
Glue on the four pieces of non stretch conductive fabric on to one of the circles of base fabric. For positioning we place the conductive fabric north, south, east and west.
Take the LEDs and attach sew them to the each hotspot. It will be one LED per hotspot. Before sewing make sure that you are sewing the negative lead (shorter leg) to the conductive fabric. (If using light bulb LEDs, it is not necessary to sew their legs to create contact. Simply placing the legs on top of the hotspots and making sure the leg and hot spot are touching is enough to complete the circuit. Be aware this is a less secure approach)