SDI12.h file

enum LookaheadMode

This enumeration provides the lookahead options for parseInt(), parseFloat().

The rules set out here are used until either the first valid character is found or a time out occurs due to lack of input.

This enum is part of the Stream parent class, but is missing from the ESP8266 core and ESP32 cores prior to 3.0 (IDF prior to 5.1).

Enumerators
SKIP_ALL	All invalid characters are ignored.
SKIP_NONE	Nothing is skipped, and the stream is not touched unless the first waiting character is valid.
SKIP_WHITESPACE	Only tabs, spaces, line feeds & carriage returns are skipped.

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#define SDI12_VALUE_STR_SIZE = 9

The maximum number of characters in a single value in a data response.

From SDI-12 Protocol v1.4, Table 11 The send data command (aD0!, aD1! . . . aD9!): the value portion must be structred as pd.d

• p - the polarity sign (+ or -)
• d - numeric digits before the decimal place
• . - the decimal point (optional)
• d - numeric digits after the decimal point
• the maximum number of digits for a data value is 7, even without a decimal point
• the minimum number of digits for a data value (excluding the decimal point) is 1
• the maximum number of characters in a data value is 9 (the (polarity sign + 7 digits + the decimal point))
• The polarity symbol (+ or -) acts as a delimeter between the numeric values

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#define SDI12_DATA_STR_SIZE = 35

The maximum length of a standard data command response.

From SDI-12 Protocol v1.4, Section 4.4 SDI-12 Commands and Responses: The maximum number of characters that can be returned in the <values> part of the response to a D command is either 35 or 75. If the D command is issued to retrieve data in response to a concurrent measurement command, or in response to a high-volume ASCII measurement command, the maximum is 75. The maximum is also 75 in response to a continuous measurement command. Otherwise, the maximum is 35.

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#define SDI12_HV_STR_SIZE = 75

The maximum length of a data response to a concurrent, continuous, or high volume ASCII.

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#define SDI12_BUFFER_SIZE = 81

The buffer size for incoming SDI-12 data.

All responses should be less than 81 characters:

• address is a single (1) character
• values has a maximum value of 75 characters
• CRC is 3 characters
• CR is a single character
• LF is a single character

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#define SDI12_BIT_WIDTH_MICROS = static_cast(833)

The size of a bit in microseconds.

1200 baud = 1200 bits/second ~ 833.333 µs/bit

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#define WAITING_FOR_START_BIT = 0xFF

A mask for the #rxState while waiting for a start bit; 0b11111111.

Possible SDI-12 States

WAITING_FOR_BREAK:

• Sensor (slave) is asleep, waiting for the data recorder (master) to hold the line high for >= 12ms. Or the data recorder has not initiated communication with a sensor in too long and needs to re-alert it.
• Starts:
  • After a sensor receives an invalid address (return to sleep)
  • When the master wants to address a different sensor
  • After line has been in marking (LOW) for > 100 ms (sensor returns to sleep)
  • After the line has been in marking (LOW) for > 87 ms (sensor awaits break without sleeping, recorder must send break)
• Ends:
  • After 12 ms break has finished

WAITING_FOR_MARKING:

• Sensor has received a >= 12ms HIGH break and is waiting for the data recorder to send >= 8.33 ms of LOW marking.
• Data recorder has finished sending a command, has relinquished the line, and is waiting for the sensor to hold the line LOW for >= 8.33 ms of marking
• Starts:
  • After line has been held continuously HIGH for >= 12ms
• Ends:
  • After the line has been in marking (LOW) for > 87 ms

WAITING_FOR_START_BIT:

• Line has been held low for >= 8.33 ms of marking
• Ends:
  • > 15 ms after the last stop bit of a command (for the recorder/master)
  • > 1.66 ms after the last stop bit between characters within a command or response

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#define SDI12_YIELD_MS = 0

The time to delay, in milliseconds, to allow the buffer to fill before returning the value from the buffer.

This may be needed for faster processors to account for the slow baud rate of SDI-12. Without this, the available() function may return 0 while we're in the middle of reading a character.

There are 8.33 ms/character, so we delay by 8ms for fast processors to allow one character to finish.

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#define SDI12_YIELD() = { delay(

A delay function to allow the buffer to fill before returning the value from the buffer.

This may be needed for faster processors to account for the slow baud rate of SDI-12.

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