Walter: The Water Butler

Proof of concept document can be found here

Dependencies: (Tested on MACOS)

1. Download nRF5 SDK
2. Download ARM GCC toolchain
3. Download nRF5x Command Line Tools.
4. Extract nRF5 SDK and rename the extracted folder to nrf5-sdk.
5. Extract GCC ARM toolchain and rename the extracted folder to arm-toolchain
6. Extract nRF5x Command Line Tools TAR file.
   • Navigate inside the nrf ommand line tools folder and install the Jlink package withing it.
   • Navigate inside the nrf ommand line tools folder and install the nRF5x Command Line Tools package withing it.
7. Check installations
   • J-Link (MAC-OS): Check if this path exists /Applications/SEGGER/JLink
   • nRF5x Command Line Tools: nrfjprog -v must output the version.
8. Export Environment variables to specifying SDK folder path and ARM toolchain path.
   • export SDK_ROOT=<PATH TO nrf5-sdk/ folder>
   • export GNU_INSTALL_ROOT=<PATH TO arm-toolchain/bin/ folder>

MAC-OS Complications: The system is going to complain that "the developer cannot be verified" for arm-none-eabi-gcc, cc1, as, collect2, ld, liblto_plugin.0.so, arm-none-eabi-size, arm-none-eabi-objcopy. Click on Cancel and then open Security and Privacy settings and click on Allow Anyway. These complains are gonna show one after the another.

Burning the software:

make flash

TODO:

• [IMPORTANT] Debug NRF52840 - doesn't stop advertising at all
• [IMPORTANT] initialize GPIO only while reading the sensor.
• [IMPORTANT] Debug app: after refresh or after close and restart of app BLE shows connected but not re4ading notifications - most probably it is the BleManager object that has gone out of scope.
• README Documentation
  • NRF softdevice and flashing instructions without debugger and with debugger
• Statistical and Analytical
  • function for analysing a day's worth of data and extracting the num. of bottles drank metric
  • triggers for interacting with the user
  • Touch sensing
• Software
  • Using NRF52840 Dongle.
    • Port Capcitive Sensor library to nRF
    • Define BLE services and characteristics
    • Finish battery level indication integration (depends on power supply design)
  • App Design
    • POC integration with BLE
    • UI Wire Frame
    • UI Design and Integration with BLE
    • run ble recorded in background
    • save data locally - use firebase
      • save device info
      • save readings
      • save calibration values
      • save settings
      • save on change
    • Main screen statistics design
• Hardware
  • Sensor fabrication documentation
  • hardware fabrication documentation
  • Aluminium or Copper Tape electrodes - didn't try but shouldn't be too different
  • 3D printed case - Going with no case design. who cares about the case anyway. The board is waterproofed
  • Power supply design
    • Coin Cells/ Super Capacitors - Super capacitor can power only for 6 minutes
      • Investigate if we can use coin cells/super capacitors
      • Calculate the usage time per charge and choose an appropriately sized battery
      • Design necessary circuitry for using coin/cell or supercapcitors
      • Fabricate and Integrate circuitry and battery with nrf52840

Power Caclulations for Supercapacitor

Current draw - 11uA for 8 s and 3 ma for 2s => ~600uA (average) Power Consumption at 3.6v = 3.6v * 600uA => 2.16mW

Energy stored in the capacitor = 1/2CdeltaV*deltaV = 0.5 * 1F * (3.6v- 2v)^2 = 1.28J Joules

Energy = Power * Time => Time = Energy/Power => 1.28J/2.16mW => 592s => ~10minutes

Decision: Use CR2032 or better rechargeable CR2032

Future Ideas:

• onboarding flow
• social - share water usage statistics with a friend, challenges etc.
• better UI