This week I finally received all the parts I ordered and was able to build and test the sensor. Below is a picture of the photodiode circuit.

It works quite well. Under blue illumination the photodiode creates a slight voltage. However, under red illumination the increase in voltage is 10 times more then under blue illumination. The use of a red filter may not be necessary because the red LEDs are not sensitive to blue light.

            Next I need to start testing the response of the LEDs to dim red light, like that produced by fluorescence. This will tell me how many red LEDs I should use in parallel (I am thinking four), and how much resistance to put in the above circuit.

            Lastly, I’ll be taking a trip to home depot soon to look for a PVC housing. I need something that can be hold the Arduino and the LEDs. Acrylic can be glued to the PVC to provide a clear window for light transfer. Another benefit of using PVC is that heating it in the oven makes it very soft. So I can reshape PVC tubes if need be.

I also received the data logger and SD card this week. It took a lot of time to figure out how the data logger works, but I now have it writing values to a text file. 

Capstone 1

I begin looking into temperature dependence of LEDs, and found that temperature does have an effect on wavelength. However, if I can identify the range of temperatures my sensor will be exposed to, it may not have a significant effect.

According to one paper by Chhajed et al. (2005), the peak wavelength for UV LEDs only changed by about 5 nm over a 100 degree C temperature range. The temperature range of my sensor will be far less then that. However, the sensor will likely be in temperatures below 20 degrees. I will look for someone who has investigated this relationship down to lower temperatures, but I’d expect the same relationship to continue beyond 20 degrees. Red LEDs appear more sensitive to temperature. Although, I am not sure if the same relationship will hold true for when LEDs are used as photodiodes.

I also looked into data loggers and found one that should work well.  http://iteadstudio.com/produce/arduino-sd-card-shield-and-filelogger-library/

Here is another link to instructions for building an amplified color sensor: http://www.robotroom.com/ReversedLED.html

Chhajed, S., Xi, Y., Gessman, Y., Gessman, L., Schubert, E. F. (2005). Influence of

junction temperature on chromaticity and color-rendering properties of

trichromatic white-light sources based on light-emitting diodes. Journal of Applied Physics. 97: 054506.

Week 14

            This week we finished up our ROV and tested it in the pool. The ROV worked, but not quite as well as we had expected. It had a few problems with buoyancy once we put it in the pool. The write up on our ROV will be along shortly.

            As far as feedback on the course, I can’t say enough good things. This class was excellent and was like no other class I have taken before. The freedom to experiment on your own, make mistakes, and problem solve made the class fun and educational. However, I do have some recommendations for future classes. I saw this past semester that many students including myself wanted to (or needed to) come in during hours other than class time. It would be good if students knew specific times when you or Jim would be around. It wasn’t really a problem for me, but I know other students wanted more time in the lab. I worked with Colin in the lab a few times, which I didn’t mind doing, but I won’t be there in future semesters. So you should be sure let students know when the lab is open or find another student you trust to open and close the lab.

            I also think that using Arduino microcontrollers would add to the class. From what I have seen it is much better then the ones we used in class that were programmed in BASIC. It will also give students the choice to use the Lego brick or an Arduino to do data logging on their AUV/ROV. The Arduino could also be used in place of a Lego brick to control an AUV, if a student wished to take on that task. I also like the programming environment much better then the Lego software. The Lego software was useable but I found myself frustrated with it multiple times. I think that Arduino code is much more realistic as well. Learning how to write code using the Arduino (or BASIC for that matter) will prepare students to use other languages, whereas the Lego picture code does not. However, the Legos provide an excellent way to construct robots. So even though the programming environment is not great, it was still one of the most rewarding parts of the class.

            As I mentioned before the format of the class was excellent. I can see a number of different courses taught in a similar format. I wish there were biology courses taught using this hands on format. It might be possible for someone to graduate from the marine biology program here at UMaine without ever handling marine life (hopefully not). My point is that the majority of our courses are lecture based. The marine science department is lucky enough to have relatively small class sizes. This is perfect for having more lab-based courses. If students were able to study live animals and perform dissections, no one would be falling asleep in class! I think this is definitely true of physics courses as well. However, the physics department does do a pretty good job of this. The labs reflect what is done in lecture and are usually engaging.

            Lastly, I enjoyed the TED talks and definitely think you should keep them in the curriculum. It’s definitely a good way to inspire students and in many cases remind them to think out of the box.

            Finally just as a side note, I will get the diver visibility data to WHOI at some point next week. There is one-year day of Tara data that I have found the TSG file for but its in four different files. I will try and process this data when I get time. I will also get the ROV write up to you as soon as I can. I have got a million different things going on, so I apologize that my progress has been slow lately.

Week 13

            I really liked the TED videos this week, especially the toaster one. We really take for granted all the things that are provided for us. I heard a comedian make fun of this idea before, “People think they are smart. But if I were to leave you in the woods, how long would it be before you could give me a phone call.”

            In the lab this week, Dana and I got very close to finishing our ROV. We have our sensors built, the frame built, and the control box completed. Really all we need to do now is fix the buoyancy of our ROV. It sits pretty awkward in the water, so there is some work to be done there. Our control box is very compact, and contains all the batteries needed by the ROV (AA batteries for the motors, C battery for the hydrophone, 9 volt for the speaker). The speaker for the hydrophone is mounted on the control box, so the pilot should be able to hear it. Dana’s recorder will also be located in the control box. In contrast my sensor will be fully contained on the ROV with no connection to the surface.

            If all goes well, we will be done next week. This is good timing because I will have to leave early on Thursday for the marine science recognition reception at 4:00pm.

Week 12

This week Dana and I made good progress on our ROV and sensors. Dana’s hydrophone is completed and will have a tether to the surface, where sound can be recorded and heard in real time. My light sensor should be completed next week. This week I mostly worked on the programming aspects of it. It will now log data from the light sensor every second. There are 512 bytes of data in the eeprom memory of Arduino, so this will provide me with about 8.5 minutes of data. The analog output is from 0 to 1023, however the eeprom memory only stores values between 0 and 255. So I will have to divide the output of the sensor by four before saving it to eeprom. I’ll put the sensor inside something to block white light (maybe a piece of PVC) and place a red filter over the top of that. I’m also interested in building a depth sensor, because it would be nice to have the depth the light measurement was taken at.

            Last night I went up to the lab with Colin for a bit and discovered that I would be able to use conductivity to detect when the ROV is submerged. When I put a wire at 5v in water with a wire connected an analog port, the output jumps right up to 1023. Next step is to test it with pool water. I was hoping I could use this same method to detect when the ROV leaves the water. However, I am worried that having 5v constantly sent to a wire in the water will drain the battery. If this were the case, I can program the Arduino to cut power to that pin after it detects 1023. In any case, I already wrote the code to wait for 1023 on analog 1 then start logging light data on analog 0. In addition I hope it will start logging depth on analog 2, but I guess I need to look into how difficult a depth sensor is.

            Overall, our ROV is coming together nicely. My next step is to solder a 5v voltage regulator and a light sensor to wires that will connect it to the Arduino board. I was worried at first, but at the rate Dana and I are going we should have plenty of time to build our ROV.

Week 11

            This weeks TED talks were really good! I didn’t know that “inventor” was a real profession. Woody Norris’s invention to direct sound was awesome. This idea was very original and has many applications in our modern society. I also like how Dean Kamen showed another side of invention that is often forgotten.

            In other news, I am exited that our robot challenges are completed and we can now move on to a new project. I feel a little rushed for time to finished the final project. I guess that’s just how it has to be; there is only so much time in the semester. However, our hydrophone should be done soon. The instructions to build the hydrophone are very easy. That should be done next week, no problem.

            I want to build the frame for the ROV and mount the waterproof box by the end of next week. I think I am going to make a turbidity sensor that can go on the ROV in addition to the hydrophone. I am looking forward to getting back in the lab to continue building our sensors and ROV. 

Week 10

            Dana and I are slowing getting through our robot challenges. Now that we have completed line runner, we have two left. I am happy to see new challenges added to the previous ones. It’s just as fun to watch other people complete challenges as it is to do them yourself. I learned this week that even though programming of the Lego robots can be frustrating, it’s totally worth it. Finally getting the code right for line runner, after working on it for a few hours was satisfying. I can only imagine the satisfaction of completing more complex tasks, like depthx (the Bill Stone TED talk). Depthx has 96 sensors! That is an enormous amount. Being able to get all these sensors to work together is quite feet. I can see the allure of working as an engineer on projects like depthx.

            The talk by Richard Feynman was awesome as well. He provided at great reminder of why science is so interesting. It is fun to look at everyday things more in depth. I think this is why I like physics and chemistry courses much more then my peers. Most of my friends find the material in these courses irrelevant. I not sure why but I find these topics very interesting. I suppose I am more curious about fundamental things.

Next week Dana and I should have our robot ready for can grab. I have some good ideas for this robot. My ideas may be a little complex, but I’ll know next week whither my ideas are feasible. I am also planning on making the robot capable of picking up a full can. I should also say that I would like to build an ROV that has onboard video. I am not sure if this requires any parts we don’t already have, but I thought I would give you a heads up.