The following materials will be needed for construction of this sensor:
-4 alligator test leads clips (10 pk $2.95)
-coin cell battery holder ($4.95)
- 3V coin cell battery
-LED light (any color you choose) (pack of 5 lights of one color, $4.95)
*Rulers, regular yarn, scissors and glue can all be purchased at a local craft store such as Hobby Lobby, JoAnn's, Michael's or WalMart
*The loom used for this project was purchased at JoAnn's. (http://www.joann.com/knifty-knitter-4-1-2-x8-1-2-spool-loom/prd45962/) Any small loom will work.
*LED lights, alligator clips and battery holder can be purchased from www.sparkfun.com
*Conductive yarn can be purchased from http://www.plugandwear.com/default.asp?mod=product&cat_id=105&product_id=228
*Coin cell batteries can be purchased wherever batteries are sold. Radio Shack has a pack of 3 batteries that costs approx $13 & battery holders can also be purchased there.
This project idea was remixed from the Circular Knit Inflation Sensor found at http://www.kobakant.at/DIY/?p=1996 and the Circular Knit Stretch Sensors found at http://www.kobakant.at/DIY/?p=2108.
Step 1: Creating the Sensor
Start by taking the regular yarn and the conductive yarn together and wrap them around the back of the first post on the loom around to the front of the post and then counter clockwise to the next post. Do this around the entire loom twice. Then lift the bottom layer of yarn over the top of the post and then wrap another layer around the loom. Continue these steps until the desired length is achieved. The knitted sensor will start to appear out the bottom of the loom. While removing the sensor from the loom, make sure to close it off by threading the regular yarn through the loops when removed from each post so it does not come unsewn.
Most looms will come with an instruction guide that is very easy to follow and also a hook that will allow you to lift the thread easily over the posts.
Once the sensor is removed from the loom, you should be able to grab onto the two tails and pull them in opposite directions and watch the sensor squeeze together.
Step 2: Connecting All the Pieces
Take the first alligator clip and attach one end to the positive end of the battery holder and the other end approximately an inch up the sensor. On the sensor end make sure to attach it to approximately half way through the sensor so half of the sensor is inside the clip.
Step 3: Connecting All the Pieces
Step 4: Connecting All the Pieces
Step 5: Connecting All the Pieces
To test if your sensor is working, pop a battery into the battery holder and stretch your sensor. The LED light should begin to light up as the sensor is stretched.
If the light does not turn on, try placing the alligator clips in different locations. A multi-meter can also be used to see the resistance when the sensor is stretched. Just take the leads and attach them to each end of the sensor and stretch. The leads will need to be on the conductive yarn when stretched to get a reading.
Step 6: Anchoring the Sensor
Step 7: Anchoring the Sensor
Step 8: Teaching With the Sensor
"The Golgi tendon organs, which are located in the tendons near their junction with the muscle. Endings of afferent nerve fibers are wrapped around collagen bundles in the tendon, bundles that are slightly bowed in the resting state. When the attached extrafusal muscle fibers contract, they pull on the tendon, which straightens the collagen bundles and distorts the receptor endings, activating them. The Golgi tendon organs discharge in response to the tension generated by the contracting muscle and initiate action potentials that are transmitted to the central nervous system." (Human Physiology 7th Edition, Vander, Sherman, Luciano, pg 338)