ML-OI-AX-I2C – Option board
ML-OI-AX-I2C, Input board to connect a simple external I2C sensor.
I2C is primarily an internal communication bus designed for communication between components on the same circuit board. For this reason, our data loggers do not include a standard provision for connecting external I2C sensors.
However, some sensor manufacturers, likely due to cost and power efficiency considerations, do offer external sensors with an I2C interface. These can be connected using the ML-OI-AX-I2C option board, provided certain prerequisites are met.
Although I2C is a standard protocol, the way devices are interrogated is not standardized. The ML-OI-AX-I2C board expects a compliant sensor to return a consecutive array of bytes containing up to two raw ADC values (signed or unsigned integers), an optional status byte, and optionally, a command to initiate a measurement.
Specifications
- Protocol: I2C
- Supply voltage: 3.6V DC
- Max number of sensor channels to read: 2
- Data type: Big-endian signed or unsigned integer (ADC value)
- ADC resolution: 8 .. 24bit (including sign bit, if applicable)
Configuration
The board can be configured via the internal terminal interface and is configured by default as example to connect to a Sensirion SHT4x humidity sensor. To connect a different type of sensor, consult the sensor’s datasheet and complete the following:
- The I2C address of the sensor.
- An optional command (up to 3 bytes) to initiate a measurement.
- The time to wait after power-on or after issuing the above command before a measurement is valid.
- An optional command (up to 3 bytes) that prepares the sensor for reading the result.
- Specify which byte in the read data contains the optional status byte (with indexing starting at 0), and define the expected masked value that indicates when a measurement is ready.
- Specify the byte offset in the read data where the ADC value for a channel begins, its resolution, any possible bit shift, and whether the value is signed or unsigned.
- Apply a factor and offset to the corresponding data logger parameter to convert the ADC value into the appropriate engineering value.
Discover the possibilities
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