This week I worked on the design review slides, as well as further specifying components, ordering, and creating backup plans. The first parts order was placed earlier this week, consisting of the microcontroller, load cell amplifier, and load cells. This will allow us to prototype the load sensor early next week once the parts come in. I was able to do some preliminary estimation on the resolution of this load cell/ADC combination (TAL221 & HX711).
This 0.085g resolution should be sufficient to measure before and after TP roll weight to almost single-sheet resolution. By my measurements, a sheet of residential 3-ply toilet paper is ~0.25g, so a sheet of single-ply commercial TP should be ~0.083g. We are shooting for a +/- 5 sheet resolution, so that seems very achievable, even in a conservative estimate.
I also put together the bulk of the design review slide deck, with supplemental information and images being provided by my groupmates over the course of the week.
We still have not totally nailed down exactly which EPC-C1G2 RFID reader we will be using. Professor Rowe has been out-of-office so we are waiting on that information. In the meantime, however, I researched a backup plan in case we are unable to borrow a reader from his lab, or it does not meet the spec needed for the Farsens tags. SparkFun produces a ThingMagic ME6-Nano-based EPC-C1G2 reader that is built to integrate with Arduino/Atmega microcontrollers, as well as USB over FTDI.
It is fairly budget friendly ($224 vs >$800 for the cheapest commercial EPC-C1G2 readers) and the only technical caveats seem to be lower transmit power/range, which would not drastically affect our project unless it was deployed commercially, and the necessity of local microcontroller/microcomputer control vs native network interface. Given the support for microcontrollers in the module, this additional technical complexity would not pose too much of a challenge to integrate. In a commercial application of SHTTR, a single industrial-grade EPC-C1G2 reader would be used that supports multiple antennas (some support 8 or more) with full transmit power to take advantage of the Farsens tags’ 5m effective range. The prototype will not be installed in a stall environment, so a shorter range can be worked with very easily.
We continue to be on schedule.
Next week I hope to:
- Prototype the load sensor once the parts arrive
- Determine a real-world resolution measurement in # of sheets
- Reach out to toilet manufacturers to see if they would send us a dual-flush valve, as this was scrapped from the design for cost reasons but would be a cool stretch goal to integrate if possible
- Schedule a meeting with Professor Rowe to discuss:
- The use of one of the lab’s EPC-C1G2 readers
- Experience working on EPC-C1G2 platforms
- Design review of the Farsens component of the project
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