HydraProbe SDI-12 Soil Moisture Sensor User Guide

HydraProbe SDI-12 Soil Moisture Sensor User Guide

Introduction

SDI-12 is a specialized communication protocol designed specifically for environmental sensors.
It’s an ideal choice for remote and low-power applications due to its minimal power consumption and reliable communication with minimal noise and interference.
Being a standardized protocol, SDI-12 allows for seamless integration of sensors and data loggers from different manufacturers into the same system, which simplifies setup and saves time and resources.
However, if you require longer communication distances, higher data rates, or need to interact with a wider range of devices, Modbus may be a better choice.
You can learn more about SDI-12 by visiting http://www.sdi-12.org
Older versions of Hydra Probe firmware may have different commands, contact Stevens Water for more information

Technical Specifications

How To Use

Using SDI-12 involves setting up a master-slave communication system between devices.
The master device sends requests to the slave devices to read or write data, and the slave devices respond with the requested data.

The basic steps to use SDI-12 are below:

1. Set up the physical connection: Connect the SDI-12 device to your data logger or microcontroller using a compatible interface cable.
   The cable should have three wires: power (positive and negative) and data.

2. Set up the SDI-12 communication parameters: Configure your data logger or microcontroller to communicate with the SDI-12 device.

3. Assign SDI-12 addresses: Assign a unique SDI-12 address to each slave device on the network.

4. Send SDI-12 commands: The commands typically include a command code (e.g., “M” for measurement) and an address (e.g., “0” for the first device on the bus).
   The device will respond with the requested data.
   Many data loggers have a “transparent mode” to communicate directly with the sensor.

5. Interpret the data received from the SDI-12 device: The data may be in a specific format or units depending on the device type.

6. Test: Test the communication between the devices and make any necessary adjustments to the commands or settings.

Addressing
The first character of any command or response on SDI-12 is the sensor address.
A lowercase ‘a’ is used to represent the address.
Each SDI-12 sensor must have its own unique address.
The default address is “0”.

a – Sensor Address
b – New Sensor Address

Identification
A request for identification will return the sensor address, part number, firmware version, sensor version, calibration, and serial number.

a – Sensor address
12 – SDI-12 protocol version STEVENSW – Manufacturer nnnnn – Part number v.vvv – Firmware version
c – Calibration xxxxxxxx – Serial number

Measurements

a – Sensor address
ttt – seconds (000 – 999) until the measurement is ready
n – number of data fields (1-9) in the measurement
aD0!| a| Send Measurement Readings
F – Soil Moisture
I – Bulk EC (Temp Corrected)
G – Temperature (C)
---|---|---
aD1!| a| Send Measurement Readings
H – Temperature (F)
J – Bulk EC
L – Real Dielectric Permittivity
aD2!| a| Send Measurement Readings
M – Imaginary Dielectric Permittivity
K – Pore Water EC
O – Dielectric Loss Tangent
aM1!| atttn| Request Measurement
ttt – seconds (000 – 999) until the measurement is ready
n – number of data fields (1-9) in the measurement
aD0!| a| Send Measurement Readings
L – Real Dielectric Permittivity
M – Imaginary Dielectric Permittivity
N – Imaginary Dielectric Permittivity (Temperature Corrected)
aD1!| a

| Send Measurement Readings
O – Dielectric Loss Tangent
P – Diode Temperature