This past week I did a few final tests on the LiPo charging hack, and then I got to work designing my own board. It’s almost done, and you can take a look at it on GitHub. Part of doing this was choosing an LED to use. I’d had a little trouble with LED selection in the past, so I reached out to Sparkfun and asked what LED they used with this chip. They very graciously responded, and gave me the part number, which was a big help. In addition to finding a new LED, I also had to look for a new microUSB slot. Our old one would fall of the board, so I am moving to a through hole soldered connector instead of surface mount. Hopefully that will make everything a little bit more stable.
I also did a lot of more administrative work this week. I reorganized part of our google drive and changed around how some of our data is stored. This sort of thing does not lead to exciting weekly updates, but is important for the health of the project.
Finally I worked with some of the new team members to get them up and running. We’re going to see some great work out of them in the coming weeks!
I mainly worked on two things this week. The first was finding some academic articles relating to my research. I had to do this for the class part of honors research. I actually found two in particular that are pretty cool.
The first is about the effects of attaching tags to small sharks on the sharks behavior. The researchers attached GCDC tags to lemon sharks in a tank, and compared how sharks with and without a tag behave. They concluded that they have to look at more than just the mass of the tag to determine if it will change the animals behavior.
The second is about using magnetometers to look at animal movement, as opposed to just using them to help with dead reckoning. They are sort of using a magnetometer with an accelerometer to try to answer some of the same questions we are trying to answer with the gyroscope.
Another charging test
I also spent a lot of time working on the battery charging. This time I used a sketch to put the Arduino into a low power state, then plugged it directly into a battery charger and a battery. This sketch brought the current draw of the Arduino down to 0.3mA. It turns out that this is low enough that the battery can charge normally while the Arduino is attached! This means that I will probably not need to make a load sharing circuit. I have a few tests using off the shelf components and sharkduinos and everything seems to be working well. The next step is to create my own board for the charging circuitry. That way it can test that it works well on it’s own.
I spent almost all my time this week introducing new people to the project. It looks like we are getting three new members of the team, and it’s very exciting!
I may introduce the new members on this blog later if they want, but right now everyone is focusing on getting them up to speed so they can start doing great work.
On the more technical side I kept working on the MOSET polarity protection circuity. I attached it to the breadboard Sharkduino and checked everything out it. It looks good and feel ready to incorporate the MOSFET onto a Sharkduino board.
Finally I kept working on finding a way to charge the LiPo while it was connected to the Sharkduino. This time I used one of Ben’s sketches to put the Sharkduino into a low power. Hopefully it draws so little current that the battery won’t notice the load, and charge normally. An Arduino running a blank sketch draws 3.70ma, this code gets it down to drawing 0.36mA. This might be low enough that the charging will work, but I’m not sure yet.
I took the summer off from the project for an internship, but the fall semester has started up so I’m back on Sharkduino!
This week I spent mostly getting things ready for the semester. I moved to a new room, and organized my supplies.
I did get a little bit of real work done too, I realized that our new batteries were wired backwards from our previous ones (ground is on the right of the connector for the old ones, but on the left for the new ones). Luckily we didn’t plug any of these backwards batteries into a Sharkduino, but I did destroy a charger before I realized what was happening. Fixing this problem was easy, but tedious. I just undid the connectors and reversed the wires going into them.
To keep this from happening in the future we are going to be more careful about inspecting new batteries before plugging them in. We are also looking at added reverse polarity protection circuitry to the Sharkduino. At our power level I think this circuitry can just be a P-MOSFET. A picture of my test circuit for that can be seen below.
Blowing up chargers wasn’t the only battery work I did. I am also conducting tests to see if we need to separate the LiPo from the sharkduino system while charging it, or if it will still charge normally while the Arduino is pulling a little current. These experiments are ongoing so I’ll talk more about them when I have results.
This is the last blog post for the semester. I will start by talking a little about the work I did over the last week, and then talk a little about the semester as a whole.
This week I tried to assemble three more Sharkduino V2.2s, and ran hardware tests on all the existing Sharkduinos. The Sharkduino assembly was a failure. I was careless and rushing so I messed up the batch. This is the down side of batch assembly, if I have a bad day I don’t just mess up one Sharkduino. This pushes us outside what I feel is an acceptable failure rate for assembly so I am thinking about how to prevent this from happening in the future. First I think that I will only assemble two at a time, doing three is too much for one session. I will also make sure I dedicate the needed time to assembling them, and not feel rushed by deadlines and other commitments. Finally I will review my assembly procedure checklist to see if I can make any improvements to the process. Also this batch may not be a total loss, some of the Sharkduinos may be repairable. I tried to repair one and broke it further, but I am going to try to repair some of the other ones before the summer.
The next thing I did this week was test all the existing Sharking with the help of the rest of the team. We did this to make sure we would not accidentally put defective hardware on an animal over the summer. Through our tests we found that all the devices were fully operational except for one V2.0 that had a broken RTC battery backup, and one V2.2 that had a defective gyroscope.
The problem with the V2.0 was that the power in pin on the IC from the battery backup was shorted to a unconnected pin. A picture of this from the microscope can be seen below. This is interesting because this is the same error that I tried to fix on one of the V2.2s, and led to me fully breaking the V2.2. When I went to repair this V2.0 I was able to use what I had learned from the failed V2.2 repair attempt and fixed this one successfully.
RTC solder bridge. (sorry for the bad picture quality)
Repairing the V2.0 was a reassuring way to end the semester after the failed V2.2 batch. While that failed batch is a minor setback it does not detract to much from this being a pretty good semester for Sharkduino. We were able to create two new iterations of the hardware, V2.1 and V2.2, that make the system more power efficient. We developed an easy and cheap waterproofing technique for tank deployments. We were able to better diagnose a lot of the issues we have been having with the tag. We repaired some of these, while others, like the LiPo charger, we have a good roadmap for fixing going forward. Finally we were able to build a lot of new Sharking. This both taught us a lot about PCB assembly, will allow us to get a lot of good data over the semester.
We have a lot of exciting plans for next semester. I will make sure to keep updating this blog with them as we do them. I may also post an update or two over the summer if I get anything for the project done. I have an internship this summer but the project will be continued by two other researchers who will be at William and Mary working on Sharkduino.