Report
- I spent much of this week reworking the hardware decisions, because I realized in our meeting Tuesday morning after walking through the hardware specs of the ESP32s and the demands of the software that they almost certainly would not cut it. I decided to open the options to boards that demand 5V input, or recommend 5V input for heavy computation, and achieve this voltage by using a boost board on a 3.7V LiPo battery. After considering a wide variety of boards I narrowed my options down to two:
- The Luckfox Pico Mini, which is based on a Raspberry Pi Pico; it is extremely small (~5g) but has an image processing and neural network accelerators. It has more RAM than an ESP32 (64MB in the spec, about 34MB usable space according to previous users) but still not a huge amount.
- The Raspberry Pi Zero W, which has more RAM than the Luckfox (512MB) and a quad-core chip. It is also about twice the size of the Luckfox (~10g), but has a native AV out, which seems to be fairly unusual, and Bluetooth LE capability. This makes it ideal for running the microdisplay, which takes AV in, so I will not have to additionally purchase a converter board.
- The decision was primarily which board to use for the camera input. Without intensive testing, it seems to me that if either are capable of running the MediaPipe/OpenCV algorithm we plan to use for gesture recognition, both would be- so it comes down to weight, speed, and ease of use.
- Ultimately I’ve decided to go with two Raspberry Pi Zero W boards, as learning the development process for two different boards- even if closely related boards, as these are- would cost more time than I have to give. Additionally, if the Rasppi is not capable of running the algorithm, it already has wireless capability, so it is simpler to offload some of the computation onto the web app than it would be if I had to acquire an additional Bluetooth shield for the Luckfox, or pipe information through the other Rasppi’s wireless connection.
- Power consumption will be an issue with these more powerful boards. After we get the algorithm running on one, I plan to test its loaded power consumption and judge the size of the battery I will need to meet our one-hour operation spec from there.
- Additionally, considering the lightness of the program to run the display (as the Rasppi was chosen to run this part for its native AV out, not for its computational power) it may be possible to run both peripherals from a single board. I plan to test this once we have the recognition algorithm and a simple display generation program functional. If so, I will be able to trade the weight of the board I’m dropping into 10g more battery, which would give me more flexibility on lifetime.
- Because of the display’s extremely long lead time, I plan to develop and test the display program using the Rasppi’s HDMI output, so it will be almost entirely functional- only needing to switch over to AV output- when the display arrives, and I can bring it online immediately.
Progress Schedule
Due to the display’s extremely long lead time and the changes we’ve made to the specs of the project, we’ve reworked our schedule from the ground up. The new Gantt chart can be found in the team status report for this week.
Next Week’s Deliverables
- The initial CAD draft got put off because I sank so much time into board decisions. I believe this is okay because selecting the right hardware now will make our lives much easier later. Additionally, the time at which I’ll be able to print the headset frame has been pushed out significantly, so I’ve broken up the CAD into several steps, which are marked on the Gantt chart. The early draft, which is just the shape of the frame (and includes the time for me to become reacquainted with OnShape) should be mostly done by the end of next week. I expect this to take maybe four or five more hours.
- The Rasppis will be ordered on Amazon Prime. They will arrive very quickly. At the same time I will order the camera, microHDMI->HDMI converter and an HDMI cable, so I can boot the boards immediately upon receipt and get their most basic I/O operational this week or very early next week.