microSDI12

A mini SDI-12 implementation for getting sensor info over UART using directional RS-485.

API

class SDI12

_init_ (pin_txd, pin_rxd, pin_direction, uart_bus_id)

• TX pin name
• RX pin name
• Direction pin name (optional)
• UART bus id (optional, default = 1)

is_active (address)

• args:
  • address: SDI-12 sensor address. Typical range: 0-9.
• returns:
  • Boolean: whether the sensor has send back acknowledgment

get_sensor_info (address)

• args:
  • address: SDI-12 sensor address. Typical range: 0-9.
• returns:
  • Tuple (manufacturer, model): The manufacturer and model name as reported by the sensor. If sensor is unreachable, returns (None, None)

get_sensor_info_ex (address)

• args:
  • address: SDI-12 sensor address. Typical range: 0-9.
• returns:
  • Tuple (manufacturer, model, version, extra_info): The manufacturer, model, version, extra_info name as reported by the sensor. If sensor is unreachable, returns (None, None, None, None)

get_measurement (address, measurement_name="M", number_of_measurements_digit_count=1, force_wait_period=False)

Sends a request for data measurement to the sensor and returns the data provided by the sensor split into an array. Supports parsing all possible values provided through multiple sequential requests on the sensor. Example:

  > aM!
  < a1329 (address + max 132 seconds of waiting + 9 expected values )
  > aD0!
  < a+1+2-3+4.1+5 (5 values read so there will be an additional request for extra data)
  > aD1!
  < a+6+7+8+9

  output: [1, 2, -3, 4.1, 5, 6, 7, 8, 9]

• args:
  • address: SDI-12 sensor address. Typical range: 0-9.
  • measurement_name: Configures the name of the query. Default is "M" as the default query is "aM!".
  • number_of_measurements_digit_count: Defines the number of expected digits in response. Default is 1 for the responses 'atttn'.
  • force_wait_period: ignore service requests between measurement request and measurement retrieval and wait for the period of time requrned by the measurement request response.
• returns:
  • Measurement data array: an array containing all the data collected from the sensor. For details on each data value, please advise sensor manufacturer manuals. If sensor is unreachable, returns None

set_timing_params (char_wait_duration_us):

Set the time needed for a character to be transmitted over UART. Used to calculate the sleep periods to ensure a character has been fully transmitted (ex. time to keep HIGH/LOW the direction and transmission pins for BREAK or MARK for SDI12). Default: 8333us

set_wait_after_uart_write (wait_enabled):

Enable/disable the sleep command after a UART write. For micropython implementations that uart.write calls uart_wait_tx_done, this sleep can be deactivated. If enabled, after UART write, the application sleeps for (char_wait_duration_us) * (number of command characters).

_send (cmd, timeout_ms=2500, termination_line=None):

The function to send command to the sensor and wait for incoming data. Mainly used for test purposes.

• arguments:
  • cmd: the command to send (ex. '1I!')
  • timeout_ms (optional): the time in milliseconds to wait for incoming response after a succesful write command to the sensor.
  • termination_line (optional): If termination_line is defined, the function will poll and aggregate incoming messages till the termination_line matches with the input. If not defined, the function will terminate with the first successfully received message.
• returns: A multiline string with all the received messages. If termination_line is not defined, the string is always one line. If no incoming messages received, returns None

Example call

>>> out = sdi12._send("1M!", 2000, '1')
SDI12 > [1M!]
 < [10015]
 < [1]
>>> out
'10015\n1'

Example

from microsdi12 import SDI12

sdi12 = None

try:
    sdi12 = SDI12("P3", "P4", "P8", 1)

    manufacturer = None
    model = None
    sensor_response = None
    address = "1"

    if sdi12.is_active(address):
        manufacturer, model = sdi12.get_sensor_info(address)
        response_array = sdi12.get_measurement(address)
        print(response_array)
except Exception as e:
    print("Exception while reading SDI-12 data")
finally:
    if sdi12:
        sdi12.close()

links

• https://docs.micropython.org/en/latest/library/machine.UART.html
• https://docs.pycom.io/firmwareapi/pycom/machine/uart/