Strain Gauge Durability Problem:

• The optimal solution is to get more of the backed silicone strain gauges.  However these are a bit expensive ranging between $8-10 each.  If we didn’t have such excess of naked strain gauges, this might be a better option.
• Another type of strain gauge is the foil type.  This type may be worth experimenting with before the productization stage because they are much less sensitive.  With our current strain gauges, I have to turn the amplifiers almost as low as they will go in order to get a good range of force.  One potential drawback is that, although I may be able to get a better range with this type, it may come at the cost of a higher dead zone.  These are approximately $27 for 5 which is still way more expensive then using our excess supply.
• Since the main problem comes from the gold strands breaking, the most cost effective solution for more durability, is to use bondable terminal pads.  These are are essentially the same thing the backed strain gauges are attached to.  With these, I should be able to isolate the delicate parts from the strain of the heavier sensor wires, by having better anchoring points on the side of where the strain gauge is attached to the metal.  It may also be possible, to mount the gauges directly on the isolator and make a packaged gauge like the ones we have.  Doing this might also help dull the sensitivity the same way the backed ones do eliminating our potential need for foil type.
• Some documentation on these terminals can be found here: http://www.omega.com/Pressure/pdf/Bridge_Completion_Resistors_RES.pdf
• I need proper measurements to determine which ones to get. I think it should be about the same size the prepackaged ones we already have.  I don’t think having smaller spacing would be very solder friendly.

Formula for strain gauge Gauge Factor.  Just found this, might come in handy.

ΔR is the change in resistance caused by strain,

R_G is the resistance of the undeformed gauge, and

ε is strain.

Repairing the hand

• Attached strain gauges to the bottom side.  Will start wiring on Monday.

Learning Electronics:

• I am about halfway through the book now.
• Multiplexer was the word I was looking for the other day when we were talking about the i2c bus.  I was surprised that the bus did not need a multiplexer in the diagrams I saw.  I think the reason a multiplexer is not needed is because there is a small one inside the i2c slave devices controller.
• Finished chapter on numbering systems, Binary Arithematic, and Boolean algebra.  This was mostly review of things I learned in COSC 101.  There are some techniques in the boolean algebra section which you can use to simplify the amount of comparisons needed to reach a desired result.  In electronics this means getting from A to B with less transistors.  In programming this could be useful in making the program run more efficiently.

Other Experimentation:

• Assembled another bridge to test the circuit board type strain gauges.
• Attached the second one to the test stick.  The glue we are using is made to work with this type of strain gauge and for whatever reason seemed to dry much fast while in contact with the insulator used.
• Soldering wire to the leads is a bit tricky but is a much less delicate process then trying to wrap the unpackaged strain gauges around the wire.
• Was worried that these strain gauges would be less sensitive but it seems that they are just as sensitive and that they play better with gain and offset adjustments better(more consistent results).
• Seems very durable.  I pulled on the wires harder then I would ever intentionally pull on them and they did not budge.  No need to put a think layer of epoxy on it,  only a small amount of glue would be needed to insulate the connection to prevent shorts.
• One side of the stick was already insulated the other was not.  I did not add any insulation to the side that didn’t have it and it seems fine.
• Since we don’t have many of these stain gauges,  I still plan to use the standard type for this prototype.  However, if I have to repair this one again, as well as future pr0totypes,  I would like to use these prepackaged strain gauges due to their ease of application, increased durability, and greater aesthetic value(no big glob of epoxy needed).  There are many sites that sell versions of these but the ones we have are really nice because they have big leads that are easy to solder to.  If you can remember where you got them from tell me, otherwise I will try to find something equivalent.
• This test stick will be used for experiments with the tactile/audio feedback system once I get the amplifiers and usb-i2c device sometime next week.

I think Clift forgot about me…. 😦  Hopefully he will come to the lunch Christina planned next Tuesday.  Its no big deal, gives me some time to read this book so I can ask more complicated questions.

• Continued setting up win machine
• Receiving weird error message in Eclipse: “The Maven Integration requires that Eclipse be running in a JDK, because a number of Maven core plugins are using jars from the JDK. Please make sure the -vm option in eclipse.ini is pointing to a JDK and verify that Installed JRE’s are also using JDK installs.” Then in the console window I’m told “Eclipse is running on a JRE but a JDK is required.” And I know for certain that the latest JDK is installed and set in the path.
• One solution is to add a -vm argument to the Eclipse.ini file. That didn’t make a difference.
• Another solution was to be sure Maven is not set up under C:Program Files b/c the space between ‘program’ and ‘files’ can cause an issue with Eclipse on windows. Next step is to remove all of the sw for the dev. environment from “Program Files” and place within a non-spaced directory.