1.2.6 On-Board Sensors

The CryptoAuth Pro Trust Platform contains a temperature sensor and a light sensor. Each of the sensors can communicate using a shared I2C bus.

Temperature Sensor

The MCP9804 is a Microchip temperature sensor that can measure temperatures in the range of -40℃ to +125℃. The device has multiple features that can be set, including the resolution accuracy and high and low temperature thresholds. The I2C address of the device has three selectable address pins. For this design, all have been defaulted to low. The default 7-bit I2C address of the device is 0x18.

The device also supports an external threshold alert signal that will trip when the temperature is outside of the low or high temperature thresholds. These out-of-range conditions can be programmed into the MCP9804 via the I2C port. Additionally, the polarity of this signal can be configured as one of the device’s features. For further details, please refer to the MCP9804 data sheet.

Microcontroller Interface:
  • I2C Signal Connections: PB24(SCL), PB25(SDA)
    • PB25(SDA) - Sercom #2. Pin Mux Configuration: IOSET2-PAD0
    • PB24(SCL) - Sercom #2. Pin Mux Configuration: IOSET2-PAD1
  • Other Connections:
    • Signal Connections: PC05(Alert), PC06(LED-Enable)
      • PC05 (Alert) - Must be configured as an input.
      • PC06 (LED Temperature Alert Indicator) - Must be configured as an output and must initially be driven high or left floating so that the LED will be off. The microcontroller can drive PC06 low when the PC05 alert signal indicates an out-of-range condition.
  • Special Considerations: The on-board light sensor, MB2 mikroBUS header and AT24MAC402 share the I2C port with the temperature sensor.

Light Sensor

The OPT3001 is a light sensor with an I2C interface. The device can operate between -40℃ and +85℃. It can measure light in the range of .01 to 83k lux using a 23-bit ADC.

The I2C address of the device has one selectable address pin. For this design, it has been defaulted to low. The default 7-bit I2C address of the device is 0x44.

Microcontroller Interface:

  • I2C Signal Connections: PB24(SCL), PB25(SDA)
    • PB25(SDA) - Sercom #2. Pin Mux Configuration: IOSET2-PAD0
    • PB24(SCL) - Sercom #2. Pin Mux Configuration: IOSET2-PAD1
  • Other Connections:
    • The INT signal is not connected to the microcontroller.
  • Special Considerations: The on-board temp sensor, MB2 mikroBUS header and AT24MAC402 share the I2C port with the light sensor.