Acquiring Prototyping Materials
The following components were ordered for prototype construction.
- Adafruit nRF52 Development Board
- 2x 500mAh Li-Po Battery
- FeatherWing RTC + SD Card Board
- 2x Feather Prototype Board
- Various accessories (USB cable, SD card, coin cell, etc)
The following components were available from Luke and Jonathan.
- Soldering Equipment
- 22 gauge solid core wire
- Multimeter
- 2x MPU6050 IMU Development Board
- 2x PLA/ABS 3D Printer (Ender 3)
- 2kg grey PLA 3D Printer Filament
- Breadboards, jumper cables
All materials were gathered for this work session, which were sufficient for bringing up all hardware components.
Adafruit Feather NRF52 Development Board and Li-Po Battery Testing
We used the Arduino IDE and Adafruit's getting started guide to start uploading sketches to the nRF52 board. The board comes with a user controllable LED, which we were able to blink. We resolved several difficulties with USB drivers and incompatible bootloader versions.
The nRF52 board comes with Li-Po battery management support. We were able to use Adafruit's example code to measure battery voltage, which matched what we measured using a multimeter. With the battery at 85% capacity, we kept the battery and board plugged in, waited 2 hours, and returned to find the battery voltage higher than before, showing that the board is able to charge the battery.
RTC + SD Card Header Testing
RTC and SD card capabilities come from the Adafruit Feather RTC + SD card header shown below.
The header was connected through I2C and SPI to the nRF52 board, and Adafruit's example code for the RTC was able to set the current datetime, and read back the datetime. Arduino's sample code for the SD card was able to create a test file, write a string of text to it, and then read back the string of text. We resolved several difficulties with the SD card's SPI chip select pin being configured incorrectly, and soldering issues with the RTC's I2C connection.
Tekscan Pressure Sensor and nRF52 ADC Testing
The nRF52 development board comes with a multichannel ADC with precision up to 14 bits. The Tekscan sensors and signal conditioning circuit from the previous work session were integrated with the nRF52 board, and the ADC was confirmed to give correct readings at 14-bit precision and a supply voltage of 3.3V. This supply voltage is within the Tekscan pressure sensor's recommended DC operating range, and the current was measured to be within the sensor's rated current.
