All credits for this amazing SDI12 module goes to @antoniovalente who created it and shared here.
This module was created to connect to SDI-12 sensors.
Many of the sensors used in agriculture use the SDI-12 communication protocol. The protocol uses only three lines, two supply and one, bi-directional, for data communication in a master-slave mode (the sensor element is slave). More details of the protocol here.
The SDI-12 block is composed of a single inverting buffer driver (74LVC1G240) with 3-state output to send data from the WisBlock serial port (TXD1). Data them goes throught a protection block a reaches the SDI12 data line (SDI12_DATA). Data from SDI12 data line, after pass the protection block, is inverted and level shifted by a simple MOSFET and feeds the serial port (RXD1).
The port pins used are:
| WisBlock IO connector PIN | Meaning |
|---|---|
TXD1 |
Serial Port TxD data |
RXD1 |
Serial Port RxD data |
IO4 |
Trasmition/Reception Selector |
Although in the protocol the supply is 12V, most sensors used in agriculture work with a 5V supply (eg the Meter Group's ATMOS, TEROS and ECHO20 sensors). Thus, the design solution was to implement a 5V DC/DC converter with extremely low quiescent current consumption (ISL9122A from Renesas).
The port pins used are:
| WisBlock IO connector PIN | Meaning |
|---|---|
I2C1_SDA |
I2C SDA pin |
I2C1_SCL |
I2C SCL pin |
IO5 |
Enable/Disable 5V |
An 18-bit analog channel (MCP3421 from Microchip) for sensors such as Irrometer's Watermark and PinoTech's SoilWatch 10 has also included.
The port pins used are:
| WisBlock IO connector PIN | Meaning |
|---|---|
I2C1_SDA |
I2C SDA pin |
I2C1_SCL |
I2C SCL pin |
The module 3V3 power is from the WisBlock switched power, 3V3_S, to power off the module for low power comsumption. Also, the used DC/DC converter has extremely low quiescent current consumption and can be shutdown by the WisBlock pin (IO5) - same pin used in the RAK1920 IO module for shutdown the 5V DC/DC conveter.
The used DC/DC convert has three operation modes:
| Operation Mode | Habilitation | Quiescent Current Consumption |
|---|---|---|
| Regulation | EN=1 or IO5=1 |
1300 nA |
| Forced Bypass | I2C selected | 120nA |
| Shutdown | EN=0 or IO5=0 |
8 nA |
| TOP | BOTTOM |
|---|---|
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