This instructable is designed to help a science teacher build a sensor that can be used to teach the principle of the golgi tendon organ. 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 how the sensor works: http://www.youtube.com/watch?v=XMa0KoAmL8M
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
The first step in creating this sensor is to use the loom to knit an approximately 8-10 inch long tube. Make sure to leave at least a foot of a tail at the beginning and end of your 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
The next step is to connect all of the pieces together with the alligator clips. This will take some trial and error to get the clips in the correct locations.
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
Take the next alligator clip and attach is approximately an inch above the last alligator clip but this time only attach it to one string of yarn and one conductive piece of yarn. The other end of this alligator clip will be attached to the positive side of the LED light.
Step 4: Connecting All the Pieces
The third alligator clip is attached to the negative side of the battery holder and approximately an inch on the other end of the sensor. This will also need to grab onto half of the sensor.
Step 5: Connecting All the Pieces
The final alligator clip will be attached approximately an inch above the last clip, once again only grabbing a single thread of conductive yarn and regular yarn. The other end will need to be attached to the positive negative side of the LED light. All of these places are approximates and will most likely need to be adjusted based on the individual sensor.
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
Once you have your sensor working how you would like it to, it's time to anchor all the pieces down. This step is optional but is more accurate to the actual Golgi Tendon Organ if it is anchored down. First take one end of the sensor and thread the tail down through a hole in your ruler and come back up through the next hole. Tie a few knots to make sure that the yarn does not go back through the hole and then tot glue the yarn down to the ruler. I chose to thread the yarn through the next hole as well and anchor it down to the back of the ruler with hot glue for more stability.
Step 7: Anchoring the Sensor
Super glue the battery holder down to the ruler as well. This completes all of the steps to make the sensor. Feel free to adapt as you see fit to meet your needs and style.
Step 8: Teaching With the Sensor
This sensor is to be used in conjunction of teaching the concept of the Golgi tendon organ. This slide is from Dr. Sydney Schaefer's graduate Neurorehab course in the Department of Health, Physical Education and Recreation at Utah State University. The regular yarn is a representation of the muscles fibers and thin conductive yarn is the afferent nerve. The sensor is a representation of when the collagen bundles are tightened and send a response to the nervous system. The light attached to this sensor shows the response that is created. The intensity of the light is an example of the amount (magnitude) of force in 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)