• Dimensions:
    • Bare board: 3.9″ x 1.737″ (99.06 mm x 44.12 mm)
    • With SD card and power plug, and wires from the sides:
      • Length:
        • 5.55″ (141 mm): straight barrel jack
        • 5″ (127 mm): right-angle barrel jack
      • Width
        • 2.7″ (69 mm): assuming ~0.5″ for wires on either side
  • Power:
    • Power consumption (sleeping @4.5V): 0.053mA
    • Power consumption (logging @4.5V): 6.7 mA 
    • Battery lifetime for standard use (logging every 10 minutes, logging takes 1 second, upper limit estimate, assuming passive sensors with negligible power draw):
        • 3xAA Alkaline (600 mAh to 1.2V/cell): 390 days (~1 year)
        • 3xD Alkaline (10,000 mAh to 1.2V/cell): 6500 days (~17 years). This is far past the battery shelf life, which will become the limiting factor (aside from field hazards).
      • In general: You need roughly 1.6 milliamp-hours of battery life for each day of data logging at 10-minute intervals.  Note these values do not include providing power to sensors.
    • Power connectors:
      • 2.1/5.5 mm barrel jack (Optional JST connector substitution)
      • USB port (USB B, the big square-ish one)
      • Automatic power supply switching: these can both be connected at the same time without damaging the logger by causing a short circuit
  • Computer–logger communications:
    • USB port: works with a FTDI USB-Serial converter
    • In-system programmer (ISP) header
  • Temperature range: -40°C to 85°C, though special batteries may be required for very low temperatures. Note that we have not tested at these extremes; rather, this is the factory-provided tolerance of our components (i.e. it is the “industrial” temperature tolerance). Testing is on the to-do list!
  • Data storage: ASCII (plain text) CSV (comma-separarated variables) file on a SD card (so more gigabytes than would ever be reasonable)
  • Clock: Maxim DS3231 high-accuracy real-time clock with internal temperature compensation.
    • Clock drift (i.e. loss of accuracy in time) is a function of temperature:
      • Between 0°C and 70°C:
        • ±2.0 ppm
        • Worst case scenario (all drift in one direction): ±63 seconds per year
        • More reasonable scenario (drift randomly distributed): ±8 seconds per year
      • Between −40°C and 0°C, and between  70°C and 85°C:
        • ±3.5 ppm
        • Worst case scenario (all drift in one direction): ±110 seconds per year
        • More reasonable scenario (drift randomly distributed): ±10.5 seconds per year
      • Likely nonfunctional for T< -40°C and T>85°C: These temperatures are beyond the published operating specs. (But they are beyond the published operating specs for the rest of the logger, too, so there!)
    • Time setting: The clock may be set using a USB connection to a computer and the “SimpleTimeSet.py” computer code.
    • Absolute time: Time is saved to the SD card as UNIX time stamps. These are represented as “seconds since midnight UTC on 1 January 1970”, meaning that they are not tied to any time zone. They can be readily converted into any time zone (or other standard representation of time), and prevent the headaches associated with using local time (which may change over the course of a year with daylight savings!)
    • Backup battery: keeps time even while power is unplugged
  • Microcontroller core: Atmel ATmega328, with a 8 MHz oscillator crystal
  • Inputs and Outputs:
    • 6 Analog I/O pins
      • 10-bit ADC (so 1024 possible increments of sensitivity, up to 16-bit resolution possible using oversampling techniques)
      • Referenced to a regulated 3.3V source
      • Can also act as digital I/O pins
      • Labeled: “A0, A1, A2, A3, A6, A7” (A4 and A5 are used to communicate with the DS3231 real-time clock)
    • 2 Digital I/O pins
    • 1 Interrupt pin
      • For sensors such as a tipping-bucket rain gauge that provides brief signals to which the logger must respond
      • Can also act as a standard digital I/O pin
    • 4 ground pins (V-). Labeled “GND”.
    • 2 pins to the input positive battery voltage (V+: ~4–5 V). Labeled “VCC”.
    • 5 pins to the 3.3V regulator, for attaching analog sensors, which are referenced to this voltage regulator, and/or for attaching sensors that need a switchable, steady 3.3V power supply. These are labeled “3V3”
    • SDA/SCL for I2C communication.
    • TX/RX Serial communication for UART communication.
    • MISO/MOSI/SCK SPI communication protocal pins.
    • ISP header with pins for a SPI interface; this allows the data loggers to be programmed with an in-system programmer, have the Arduino bootloader installed for easy programming over USB, and/or for external SPI devices to be attached
    • All of the 9 I/O pins can be used for serial communications with the Arduino Software Serial library. Communication can occur via both standard (TTL) and inverse (RS232) logic. We are in collaboration on a SDI-12 library for Arduino to allow this common one-wire 1200-baud interface to work with our loggers (and Arduino-based devices in general) as well.
  • Human interface:
    • Indicator LED: flashes status messages
    • Reset button: restarts the data logger
    • “Log Now” button: tells the logger to take a reading immediately; this is good for testing whether or not it is doing what you want it to do!