Category: Team Status Reports

Progress

Earlier this week, we did the final assembly of the watch and brought it out to Schenley Park to do a field test:

Apart from this field test, all of our team members have been occupied with other obligations and courses wrapping up this week. We have no new risks, and no major design changes have been made.

Testing recap

We’ve done quite a few formal and informal tests throughout the development of Landhopper. Aside from our continuous basic testing of the device’s operation indoors while developing its firmware, we often made quick excursions out of the lab in order to check the GPS behavior. These were done at various times of day, and in varying weather conditions (in the first photo below, it was raining, so we placed the development board in a plastic bin to keep it dry). These tests were very informal (we rarely recorded our results other than taking photos) but they proved to be extremely effective for iterative testing of our code: we caught many, many GPS and battery-related bugs this way.

Besides these very informal tests, our formal tests were more diverse: for example, the characterization of our motor power source was one of these, and from the test we found that while mechanical energy harvesting with a motor is definitely viable energy wise, it would take much more iteration to produce a version that is small enough to fit in a watch. This confirmed our choice of the solar panel as our power source, so no design change was made as we had already designed much of the watch with a solar panel in mind.

Our aforementioned Schenley Park field test was looking for several pieces of information: how accurate our GPS logging is, how reliable our SD card saving and loading is, and how long our battery lasts. From the test, we found that our GPS logging accuracy and capacity is within our requirements and that our SD card loading works correctly and quickly. We discovered after the test that we had accidentally set the GPS to log more often than we had intended to, which definitely affected our battery life results, but accounting for this error mathematically we determined that our battery life should still meet our requirement. Design wise this test resulted in few changes, as it mainly served to confirm our requirements; however, it did lead to us correcting the GPS log interval,  along with determining that our GPS antenna should be placed on the side of the watch in such a way that it faces the sky when the user’s arm lies completely slack.

Our comfort test is our next planned formal test. We have not been able to run the test yet, but we plan to have several participants wear the watch in several environments and answer a questionnaire about it. This test will serve to check our weight and comfort requirements and also to inform any final changes to the design of the watch’s case.

We have no new risks that we are worried about, nor are there any changes we have made to the design of the system.

We have run some tests on GPS location accuracy, walking around CMU campus in various conditions and testing to see how long it takes to get a lock and how accurate this lock is. For accuracy, we will compare Landhopper’s location fix against a known-good and known accurate position source, a U-Blox ZED-F9P (which we will borrow from Roboclub). The ZED provides very high-accuracy and high-precision RTK-GPS position fixes, accurate down to a few centimeters, so it is an ideal “ground truth” for comparison.

As for actual cases we will test, we want to experiment with various positions for the antenna on the wearer’s wrist to determine which results in the most accurate fix. Simultaneously, we hope to test the amount of battery taken to get a fix, as well as the amount used in typical usage by logging the battery levels along with each location store. We hope to be able to analyze both of these results in order to meet our use case requirements of a week-long hiking trip with high-fidelity tracking, by synthesizing the position data from Landhopper with the power consumption data and visualizing it with QGIS.

Through the course of the project, we have done much analysis to see what energy harvesting source we should use. Though we tried several times to figure out the best way to attach the piezo tiles to a metal band, they always popped off of the band when it was bent to the necessary curvature. We’ve gone through a few versions of the gearbox for the motor generator option, but all of them have either. At the current stage, we’re thinking of cutting our losses on the piezo option, but we’re still going to give the motor option one or two more iterations. If we get it to the point of generating any amount of useful power, we’ll definitely give it a proper comparison against the solar option by determining which harvests the most energy in both indoor and outdoor scenarios.

Solar harvesting is showing to be very fruitful so far: the 15mA we have achieved from full sunlight far outpaces the maximum power generation given in our referenced papers for the piezo and motor techniques (the most given was around 9mA). We will further test with different orientations and positions of the solar panel on the watch case (like with the antenna) to determine which results in the most power generation outdoors. We’ll visualize this data alongside the position and other parameters to make sure we’re meeting our planned requirements.

This week, we assembled and tested our prototype PCB. Twain did the initial SMD components, Gary assembled the through-hole components, and Carson modified the software to fit the new layout and did the testing. Fortunately (and maybe surprisingly), we were able to confirm that all of the board functionality that we wanted worked, including:

• The debug/programming interface
• The GPS module
• The display
• The low-power external crystal oscillator
• The energy harvesting (not integrated)

There were a few layout problems that can be fixed in the finalized PCB, but this was still highly successful. Below is an image of us testing the new development board outside, showing both a successful GPS fix and the functioning display.

This week we made the major step of finally ordering the first revision of our PCB, and we also made incremental progress on the firmware and energy harvesting components of our project. Firmware changes include a refactoring to improve communication with the GPS. On the energy harvesting front, we received our solar cells so began working to characterize them and compare them to to the piezoelectric and generator-based options.

We have no new risks which have arisen. There have been no changes made to the design of the system or to the schedule.

The main risk that we see right now is the PCB not working well for our project, which is being managed by putting in this order early enough that we can edit the design and get another PCB when we see what we don’t like about this design.

There have been no changes made to the design of the system or to the schedule.

A was written by Carson Swoveland, B was written by Twain Byrnes, and C was written by Gary Bailey.

Part A: Our product can work in a variety of environments around the globe. It can track location anywhere around the world with an open sky by using satellites from several different countries (GPS, GLONASS, Galileo, and BeiDou). In addition, the lack of any emitted signals means that it can still be used even in countries with more stringent requirements on radio spectrum use. Areas with limited or unreliable power infrastructure can still be served using the energy harvesting functionality.

Part B: Our product solution meets cultural needs surrounding privacy and data control. In cultures such as American culture, where a strong emphasis is placed on individual autonomy, the watch becomes a valuable tool that aligns with these cultural values. Our watch meets these needs by storing all data locally on the device. This feature directly caters to cultural preferences that prioritize autonomy and control over one’s information. Users from such cultural backgrounds may be more inclined to adopt a tracking device that respects and aligns with their cultural values of safeguarding personal data.

Furthermore, this local storage prevents real-time tracking and cloud-based sharing, aligning with cultural norms that prioritize the privacy. Landhopper meets this cultural need by offering a tracking solution that is not only functional, but also respects and aligns with the cultural values of privacy, autonomy, and control over personal information.

Part C: Due to the fact that Landhopper has an on-board energy harvesting system, the environmental impact of continuously using it is minimal: no external power input is needed to keep it operational for long stretches of time. In terms of the manufacturing process, Landhopper is as environmentally-friendly as electronics can be. In our prototypes, we have taken care to use the least toxic resources possible, such as lead-free solder for the circuitry and PLA for the case. While it is inevitable that there are negative environmental impacts from the manufacture of electronics, the manufacturers of several of the core components used in Landhopper (STMicroelectronics and U-blox) have made commitments to minimize their carbon emissions.

This week, we had some major successes with prototyping the motor-based energy harvesting scheme and finishing the breadboard prototype of the digital hardware.

We have no new risks that we are worried about, nor are there any changes we have made to the design of the system.

The biggest risk we see right now is the timing on the shipping of necessary components. We have accounted for this as part of our general shipping time / slack in our Gantt chart, but we will mitigate similar future risks by attempting to figure out what we need earlier, and by utilizing Slack to communicate these needs earlier.

We did not make any specific changes to the existing, but we decided to make a design decision on our battery system: we will move forward with a LiPo battery. The only costs from this are in purchasing one such battery.

There have been no changes to the schedule.

For this status report, we were asked to answer additional questions. A was written by Twain, B was written by Gary, and C was written by Carson.

Part A: Our product solution addresses a critical need in the context of public health, safety, and welfare. The prolonged battery longevity ensures that individuals, especially those engaged in outdoor activities or requiring continuous location tracking, can rely on the device for an extended duration without the concern of sudden power depletion. Simultaneously, the watch’s emphasis on user privacy safeguards individuals from unauthorized access to their location data, mitigating potential risks associated with personal information exposure and contributing to the psychological well-being of the user. By prioritizing both functionality and privacy, this GPS watch contributes to the overall well-being of users, aligning with the broader goals of public health and welfare by providing a secure and dependable tool for personal tracking without compromising privacy or safety.

Part B: The most prominent existing solutions to the issue of a user wanting to keep track of their own location history involve sending the user’s location data to a companies who have stipulated in their privacy agreements that they are free to sell the data to others as they wish. To many people, this is an uncomfortable arrangement, as over time, more and more fears surrounding “big data” and data-selling arrangements like this have become prevalent. Our watch addresses this issue, as it allows the user to track their path while all of the data involved is stored on the watch itself, without ever being uploaded to the cloud.

Part C: Current watches that integrate both GPS and energy harvesting technology are very expensive (e.g. the Garmin Instinct II, which sells for ~$400). Other watches that have GPS technology (e.g. the Google Pixel Watch, at ~$200) don’t integrate energy harvesting, and thus have limited battery life as a result. Landhopper’s feature set is specifically designed to fill the niche of a wearable but long-lasting GPS, while trimming out features like Bluetooth and phone connectivity to avoid expensive transceiver modules and additional processing requirements.

The most significant risks we see right now are with the energy harvesting and its interaction with the GPS. The energy harvesting method we intend to employ may not be as efficient as we were hoping, since we were unable to find the correct kind of piezo tile, and generally we would not expect to get the same results as the paper. We are managing this risk by looking into alternative sources of energy harvesting. The other risk that we see right now is that GPS is a very finicky system, and we are worried that the voltage jumps from the piezo tiles will create a large amount of noise that may throw off the GPS signal. This is also being mitigated by looking into other potential sources of energy harvesting.

No set changes have been made to the system as of right now.