Fully open-source and open-hardware data logger tailored for logistics applications i.e. for cold chain monitoring systems.

Please check Medium post with the extended description of the project.

Firmware repository

Schematics, PCB, enclosure, BOM, assembly documentation

Key risk metrics:

• Temperature/Humidity Sensirion SHT3x
• Ambient Light Sensor TI OPT3001
• Shock Sensor - Accelerometer NXP MMA8452Q

Communication:

• USB-C:
• MSD: Device works as a flash drive to direct log read on PC
• CDC: Console for debug and firmware bootloader
• NFC for control through mobile app ST ST25DV04K

Security:

• Hardware crypto Microchip ATECC608A for:
• Firmware encryption for bootloader
• Log data encryption
• Authentication (X509 certificates for IoT platforms)

Power:

• Powered by 2xAAA batteries or USB-C (reverse polarity protection, OR source selection)
• Low Power Consumption: Ultra-low power architecture, ~ one year of data acquisition

Additional Features:

• 4MB SPI NOR Flash AT25DF321
• RTC Clock: accurate 32.768Hz quartz oscillator
• LED: Simple indication for device states

Main MCU

• Microchip ATSAMD21E18 - 32-bit ARM Cortex-M0+ MCU, 48MHz, 256KB of flash and 32KB of SRAM. Satisfies AEC-Q100, recommended for Automotive.

Firmware

The firmware is written in C with a bare-metal approach and exclusively uses static memory allocation. It is developed on top of the Harmony v3 Embedded Software framework. Developed with MPLAB X IDE, XC32 compiler.

Main architecture

The source code adheres to an asynchronous, non-blocking programming style designed to achieve ultra-low power consumption.

The core mechanism revolves around handling asynchronous events from a queue and entering a low-power sleep state when the queue is empty. New events are enqueued either through interrupts (e.g., cron-scheduled sensor reads) or through the main system loop.

The architecture incorporates the following key concepts:

• Event Loop
• Actor Model - aka Active Object
• Finite-state machine - Mealy + Moore implementation

To streamline development, an Active Object + FSM library has been implemented and is maintained in a separate active-object-fsm repository.