Week 9

This week we focused on testing various aspects of our bandage starting with the illuminance of the LED matrix.  We used a dark closet along with a light meter, as shown in figure 9.1, to take the measurements displayed in table 9.2 below.

Figure 9.1 - Light meter being used on the PDT device (dark room not visible)

Table 9.2 - Illuminance of LED matrix in lux

As is shown in table 9.2, reading were taken directly on top of the matrix as well as 1mm above the lights.  Interestingly, the illuminance was greater when flat on the matrix meaning a final product must have the LEDs as close to the patients skin as possible.  

In addition to how much light the matrix gives off, we testing two different batteries with the matrix.  Figure 9.3 below shows both batteries next to the PDT device.

Figure 9.3 - 6v camera battery (bottom), 6v lamp battery (top)

We plan on using the larger battery for sustained tests while the smaller one will be used for demonstrations as it is close to the size a battery on the finished product would be.  

The reason the large battery was selected was for its capacity.  The LED matrix requires 1.7 volts and draws a current of approximately 2 amps overall.  As stated above, this capacity allows for sustained testing of the matrix.  Because lamp batteries predominantly come in 6 volts, a smaller battery that has a 6 volt drop was selected for ease of use when changing batteries.  In order to supply the proper voltage to the matrix, ohm's law (V=IR) was used to determine that a 172 ohm resistor was needed between the 6 volts supply and LEDs so as to not blow the diodes.

We are working hard on our presentation and final report and look forward to sharing our design next week!

-The team

Success!

As we hooked the bandage up to a power supply and flipped the switch, we were met with 90 shining LEDs - in other words: success!  The hookup and then lit-up matrix is shown below in figures 8.5 and 8.6.

Figure 8.5 - Bandage setup attached to power supply

Figure 8.6 - Lit-up LEDs at 1.7 volts

The matrix works as well as expected!  When folded, all of the LEDs stay lit as shown in figure 8.7 below.

Figure 8.7 - When bent, the matrix still works

This step marks a major success on our project.  While we have a wearable setup, powering the LEDs is still a concern as this test was run using a large, variable DC power supply.  In the coming days we will test multiple batteries to make the device truly portable.  

We look forward to future successes!

-The Team

Week 8

This week we worked on sewing the LED strips to a bandage.  While the current design requires 2 Amps of current, a large amount, we decided that it is best to focus on the physical rather than electrical design so we can run tests sooner.

The original plan called for using a sewing machine to stitch the LED strings to the bandage, but it was quickly discovered that the sewing machine would not work.  As it turns out, the plate that holds down fabric on the machine did not leave enough clearance for the LEDs.

Luckily, we were able to hand sew the strips to the bandage.  Figure 8.1 below shows Brandon getting comfortable with the stitch.

Figure 8.1 - Brandon sewing a strip of LEDs to an bandage

A little perseverance went a long way and the major sewing was finished within 24 hours.  Figures 8.2 below shows all of the sewn strips.  

Figure 8.2 - The LED matrix sewn to a bandage

In an attempt to organize the ends of the thread, Becky pushed each end through the bandage in organized rows.  This not only looks much cleaner, but makes wiring the matrix much more manageable.  Figures 8.3 and 8.4 below show Becky at work as well as the finished product.  

  Figure 8.3 - Becky organizing the loose ends of the thread

Figure 8.4 - The final LED matrix mounted on a bandage

Hopefully this design will stand up to testing!  We look forward to testing the light output of the matrix!

-The team

Week 7

This week we went through power testing our LED strips.  There are unique challenges presented in powering this matrix: the current/simplest wiring of the strips requires 2 amps at 1.7 volts.  This high amperage is difficult to supply safely and comfortably. 

In order to test configurations of the matrix, the strips were placed on cardboard in the correct order to allow an easily reconfigurable testbed.  Figure 7.1 below shows the testbed. 

Figure 7.1 - LED strips laid out on cardboard for testing

Unfortunately, it turned out the LEDs were difficult to manage on the improvised testbed and continually shorted.  While discouraging, a testbed was necessary and luckily a new idea evolved - a PCB breadboard.  The thread was pulled through the holes in a PCB with the positive and negative sides separated by a number of holes.

While still a bit difficult to keep the wires from crossing, the new testbed was met with success!  A shown in figure 7.2 below, the LED matrix lights up when powered by a variable power supply. 

  Figure 7.2 - Illuminated LED matrix on a PCB

Despite the great stride forward, there are still many difficulties to overcome.  The assembly still needs to be mounted to a bandage and a final, more accessible power supply must be decided upon.  The mounting to a bandage will be tricky as an entire strip of LEDs goes out if two wires cross.  

Hopefully, we will continue to be met with success!

-The Team

Week 6

This week we revisited a past approach with a twist - we glued the LEDs to conductive thread, but instead of in one large matrix, there are 15 strips.  Even further, the thread is not braided!  We decided to take this approach because we noticed that the pressure put on the matrix from the LEDs and large braids was too great. Becky and Ariana are assembling the new matrix in figure 6.1 below.

Figure 6.1 - Becky and Ariana gluing the LED strips

This approach proved to be working after the strips were allowed to dry.  Testing and some cleanup revealed working LEDs.  Figure 6.2 below shows the finished strips along with the second half on the loom.

Figure 6.2 - Finished LED strips along with drying LED strips

Next week we have many challenges to face: sewing to an bandage, powering the matrix, and measuring the light intensity given off by the matrix.  Hopefully we will be met with success!

-The Team

Week 5

     This week marks our second attempt at creating the LED matrix.  As we found many problems with the conductive thread and epoxy combination, we decided to try soldering LEDs directly to copper wire.  This method should allow greater flexibility (the thread became surprisingly brittle) as well as an easier way to fix errors (solder can be taken off).  The start of the new matrix is shown is figure 5.1 below.

 

Figure 5.1 - Beginning of soldered LED matrix

     That's all we have for this week!  On next weeks agenda is testing our matrix for light intensity.  

-The team

Week 4

This week was full of surprises!  We started (and finished.. sort of) the assembly of our first device.  It all started in lab with braiding thread.  As shown below in figure 4.1, Becky and Ariana are hard at work braiding three strands of thread together to minimize the resistance.

 Figure 4.1 - Ariana and Becky braiding to make a total of 15 braided triplets

We decided to glue the LEDs to the strands the next day when we had enough time to get through all of them, or so we thought...  As it turns out, the loom we have has spaces too close together.  While it works great for one row of LEDs, the pressure of multiple rows forces the entire design to buckle.  The beginnings of the matrix is shown in figure 4.2 below.

Figure 4.2 - The first few rows of LEDs

Conditions got worse by the row.  Shown in figure 4.3 below is our close to finished first design. 

Figure 4.3 - Almost finished first attempt

While our first method for building the matrix may not have worked out (we're not entirely sure yet - it's still drying) this week was definitely a learning experience!  We have already begun to design new production methods and hopefully we will be able to start finalizing and implementing one of them next week. 

-The team

Braided Model

Today is a very exciting day for our group!  We successfully built a single-row prototype of our design!  This prototype contains 6 LEDs and two lengths of thread.  Figure 3.3 below shows the test strip lit up.

 

 Figure 3.3 - Test strip lit up

We started assembling the model last night.  The procedure gave us good practice for the final design.  Figure 3.4 below shows our solution for drying the glue.  We did not want to use a blow dryer for fear of blowing the LEDs off the string, so we used a curling iron!

 

 Figure 3.4 - Creative glue drying solution

We're making final preparations for our full model, so sit tight and we'll report back ASAP!

-The team

Week 3

This was a very productive week!  To start, we conquered the thread resistance problem.  We measured the resistance between three distances of thread in three different configurations: a single strand, a twisted pair and a braided triplet.  The results are shown in table 3.1 below.

Table 3.1 - resistance of thread by number of strands

It is apparent that the more strands braided together, the less resistance there is in a given length of thread.

The second breakthrough we made was lighting up an led using the thread as wire as shown in figure 3.2 below.

Figure 3.2 - led illuminated using conductive thread as wire

Prior to this lab session, we were successful in making the led function as part of a circuit.  We discovered that the issue was the assembly mechanism we are using to build the led matrix.  This mechanism is a metal, therefore conductive, loom.  As the loom is conductive, it was shorting the circuit.  

These advancements should allow us to sting the loom over the course of the week, possibly gluing the LEDs to the matrix before next lab.  

-Brandon

ps. Here is a video of the led turning on and off:

Conductive Thread Woes

     I was testing out the conductive thread we have available to use and I found what may be a problem: the resistance per length of thread is so high that when a power source is connected a small distance away from the LED, it does not light up!  Upon further investigation, I found that when the probes of an ohmmeter are placed approximately one cm apart, the resistance is between .5 and 1 ohm - an acceptable amount.  However, when the probes are placed approximately 10 cm apart, the resistance jumps to between 5 and 10 ohms - too high for reliable usage. 
     One solution to consider is braiding multiple strands of wire together in an attempt to lower the resistance per length of thread.  Another possible solution is switching to another material - maybe even metal wire - to build the prototype.  This solution would allow light measurements to take take place in order to see if the project is worth pursuing in the future. 

-Brandon

Week 2

Last week in class we met our advisers and were able to choose our groups and projects. We created our blog and our bios page.  The project we chose was the Wearable LED for Photodynamic Therapy.  
Our challenge is to create a wearable LED device that can be used with pc4 to treat psoriasis.  By using 100 LEDs, a lilly pad, conductive epoxy, and conductive thread, a prototype can be built.  
During week 2, we met with our instructor and discussed ideas to build the LED strip.  We discovered many potential problems while brainstorming.  Some tools we still need to properly build the device include a multimeter, and model tweezers.  The LEDs are very small which makes it incredibly hard to glue them to the string by hand.  The use of tweezers will decrease the difficulty of this task.  Also, we do not know which end of the LEDs is positive, and which end is negative.  Before we can proceed, our group would like to be certain which end is which.  We also needed a ruler to measure the distance apart the LEDs needed to be mounted. Another problem is that the loom on which we were to build the device is needed for other groups.  Since the glue takes four hours to properly adhere, a new mount needs to be devised.  The mount should be non-conductive and portable.  Some ideas that were suggested include cork board and blocks of wood. 
We will obtain the needed devices, and bring them to lab next week.  This way we will be able to begin building the device immediately.

 First attempt at stringing LEDs on a Nativie American loom