This instructable is designed to help a science teacher build a sensor that can be used to teach the principles of the vestibular, which is located inside the cochlea. It includes step-by-step instructions on the construction of the sensor as well as information on the principles it can be used to teach. This video demonstrates the working sensor: http://www.youtube.com/watch?v=yqqp0mtA83o
This sensor's design is based on the Stroke Sensor found at http://www.kobakant.at/DIY/?p=792. Please visit this site for more examples and information.
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Step 1: Materials Needed
This following materials will be needed for construction of this sensor:
-piece of Easy Felt (this felt is a bigger sheet & also a little stiffer than regular felt)
-piece of regular felt
-stretch conductive fabric
-wonder under (iron on)
-neoprene (this need to be ironable and thicker, not the plastic sheet kind)
-conductive thread ($34.95-$39.95)
-2 LED lights (any color you choose) (pack of 5 lights of one color, $4.95)
-2 sewable coin cell battery holders ($4.95)
-2 3V coin cell batteries
*Needles, scissors, Elmer's Glue, Wonder Under, and felt can all be purchased at a local craft store such as Hobby Lobby, JoAnn's, Michaels or WalMart
*LED lights, battery holders and conductive thread can be purchased from www.sparkfun.com
*Coin cell batteries can be purchased anywhere batteries are sold. Radio Shack has a pack of 3 batteries that costs approx $13
*Stretch conductive fabric as well as the thread can be purchased from www.plugandwear.com
Step 2: Making the Conductive Strips
Take your piece of Neoprene and decide the size that you want your sensor to be. In this example, the Neoprene piece used was approximately 4x6. A rectangle is the best shape to choose.
Take a square of the conductive fabric, it doesn't have to be huge, just large enough to cut 4 rectangles. These rectangles will be anchored to the back of the Neoprene on the four sides. Take the piece of conductive fabric and iron onto a piece of Wonder Under. Cut this into the four sensors and iron those four pieces to the back of the piece of Neoprene. Once again the size does not really matter but these pieces cannot touch.
Step 3: Conductive Thread
Next, take the needle (the bigger the better because you will be sewing through thick layers) and thread it with two lengths of conductive thread. No knots need to be tied. Start by going down through the top of the Neoprene through the conductive fabric sensor and pulling until the end of the strings leave about an inch. Then come back up through close to where you started and make sure to hold onto the conductive thread ends so they do not pull all the way through. Cut the thread to match and repeat the steps in a line along the conductive thread. You can make them sparse or tighter together. Repeat these steps on all four of the conductive fabric rectangles.
Step 4: Filling in the Sensor
After the four outside sensors have been sewn, the inside needs to be filled in using the same technique. Start about an inch away and make sure not to sew these to the conductive fabric. Sew approximately three parallel lines of stitching to fill in the center of the sensor. Just remember that if one thread in the center is touching one of the outside threads that is hooked to the conductive fabric, the light will turn on. The thicker you make the inside, the more likely this connection will happen without you meaning for it to happen.
Step 5: Attaching the Batteries & LEDs
The next step after the sensor has been sewn is to attach the batteries and the LEDs. Take the piece of Easy Felt decide on how you would like your sensor to be laid out. The picture above shows the layout that was used for this example and also the connections that need to be made. The large rectangle is the Easy Felt and the smaller rectangle is the stroke sensor.
The positive (+) end of the battery holder will be attached to the positive (+) end of the LED. The negative (-) side of the LED will be attached to one conductive fabric strip while the negative (-) side of the battery holder will be attached to the opposite side's conductive fabric strip. This layout will be used for both LEDs and battery holders. When sewing through the LEDs and the battery holders, make sure to create a strong connection by sewing through at least three times.
When sewing to the conductive fabric, make sure that the stitching goes through the fabric a few times before ending. This will make sure that a connection is made.
There is a trick however, in a felt patch needs to be used to make sure that the stitching does not cross. The easiest way to accomplish this is to sew one circuit completely and then work on the other one. When you are sewing the second circuit and come to the point where you need to sew on top of the other sewing you have previously done, take small piece of felt and sew through only the very top layer so that no stitching comes all the way through. Then lay the patch in place over the previously completed stitching and continue on to the sensor.
Step 6: Testing the Sensor
Once all of the stitching is complete, pop in the batteries and test out the sensor. Stroking it one direction should turn on one of the lights and stroking it the other direction should turn on the other light.
If for some reason the light is constantly on, try separating the end threads from the center ones. This should break the constant connection if there is one. Once you have everything working, it is a good idea to use some Elmer's glue and anchor down your knots on the back to make sure that they do not move or fray.
Step 7: Teaching With the Sensor
This sensor is to be used in conjunction of teaching how the vestibular works. The vestibular is located inside the inner ear. The graphics above are book examples of what this sensor can teach in a visual hands-on way. The movement of the hairs detect the direction of motion turning on the light in the direction that hairs on the sensor are moved. This movement is demonstrated by the hand moving across the sensor. (See video at http://www.youtube.com/watch?v=yqqp0mtA83o). The hand will act as the tectorial membrane so that the hairs move relative to the basilar membrane to turn the light on which represents activating the neuron.
"Changes in the motion and position of the head are detected by hair cells in the vestibular apparatus of the inner ear, a series of fluid-filled membranous tubes that connect with each other and with the cochlear duct. Information about hair-cell simulation is relayed from the vestibular apparatus to the brainstem via the vestibular branch of cranial nerve VIII. Vestibular information is integrated with information from the joints, tendons, and skin, leading to the sense of posture and movement. Unexpected inputs from the vestibular system and other sensory systems can induce vertigo (Human Physiology 7th Edition, Vander, Sherman, Luciano, pg 253-255).