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• Current Consumption and Battery Life Estimation

  Josh Joy • 07/03/2023 at 16:59 • 0 comments

  Using the Nordic Power Profiler kit 2

  When BLE was connected but not transmitting any data, it consumed 41 milliCoulombs per minute.

  When BLE was connected and transmitted data twice, once to open the tap and once to close the tap, it consumed 45.8 milliCoulombs per minute.

  Let's assume that the tap was opened and closed 4 times in an hour:

                           = [ 45.8 X 4   +   41 X 56 ] mC / hour

                           =  2479.2 mC / hour

                           =  0.6886 mAh / hour

  Considering a battery size of 500mAh = 500 / 0.6886 hour

                                                                  = 726.11 hour  = 30.254 days

                                                                  = 30 days 6 hours

  Note that I am still figuring out how to use the low-power modes of the nordic nrf52 chip, I am quite confident to optimize the battery life to 3 months minimum. 

• Current Consumption and Battery Life Estimation

  Josh Joy • 07/03/2023 at 16:57 • 0 comments

  Using the CurrentWave / microCurrent Gold

  When the Sensible Flow unit is connected to the Base unit via BLE, it consumes 600uA to sustain BLE connection in low power mode and also the IMU in low power. 

  The IMU in low power mode is setup activity-based interrupt, the IMU sents an interrupt signal when motion is detected. An interrupt service routine runs which transmits the pitch, roll and yaw value of Sensible Flow. During transmission the device consumes 1.2mA. 

  Only when the Tap is rotated it consumes 1.2mA for 2.5 seconds and goes back to sleep meaning 500uA.

  Let's assume the tap rotations are 10 min per day 

                                                   = [ 1.2mA X 10 min + 0.6 mA X ( 23h 55m) ]  / day

                                                   = [ 12mA X 0.0167h + 0.6mA X 23.91h ] / day

                                                   = 14.54 mAh/day

  Considering a battery size of 500mAh = 500 / 14.54  day

                                                                   = 34 days 9 hours

• The 2nd Prototype

  Josh Joy • 07/03/2023 at 16:56 • 0 comments

  The 2nd iteration used a CR2450 Coin Cell battery, along with Arduino Pro Micro, which helped make things much more compact. 

  Size comparison between the 2nd Prototype and the First.

• The First Prototype

  Josh Joy • 07/03/2023 at 16:55 • 0 comments

  The first prototype was built using components I already had in the workshop, it used a AAA battery as the power source. An atmega328p IC on a breadboard, along with an MPU9250 IMU and HC-42 BLE module. I used this prototype to verify if I could accurately estimate water usage indirectly from the tap handle movement using an IMU, and the test was a success.  

• Figuring out the components

  Josh Joy • 07/03/2023 at 16:54 • 0 comments

  The first Sensible Flow prototype design process involved selecting components (Inertial Mass Unit, Bluetooth Module, Microcontroller) based on ease of availability and ease of use. Future iterations will use components that use lower power and cost lesser, integrated into a custom PCB.

  Sensible Flow

  Sensible Flow estimates water usage based on the position of the tap handle after it has been rotated/moved.

  1) Arduino Pro Mini 8Mhz 3.3V

  2) HC-42 BLE Module

  3) MPU9250 IMU

  Base
  

  The Base unit displays the estimated total water consumed for a particular day (updates real time) and sends data to the internet via WiFi to monitor water consumption for the whole year. Multiple Sensible Flow units can be connected to a single Base unit and monitor water usage across various taps.

  1) ESP32 WROOM 16MB

  2) 0.96 Inch OLED

  3) Hi link 3.3v 3W

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