SDI-12 on WisBlock

WisBlock
1

I want to use the WisBlock to read out an SDI-12 sensor. Does anyone know if it is possible using the RS485 interface (Transmit data efficiently with the LoRa®-powered RAK5802 module – RAKwireless Store)? I saw somewhere on the internet that someone used only the one connection from the RS485 differential pair, and connected that to the SDI-12 sensor. The other connection from the differential pair is then either left floating, grounded, or pulled to Vcc.

Or does RAK maybe plan to make an SDI-12 interface card for the WisBlock?

2

Hello JP,
I doubt that it will work with the RAK5802 module, but could be worth a try.

We are collecting customer feedback about interfacs/sensors that they would like to see supported by WisBlock and I will add your request to our list. But I cannot promise you anything.

3

I tried to speak SDI-12 using the RS485 connector board (RAK5802) today. So far I’m not successful. I’m not sure if I should use A or B, and if it’s fine to pull the other terminal to 3.3V or to GND. And I can’t find the Arduino forum post that described the setup.

Next step would be to try Arduino-SDI-12 but I’m not sure if the WisBlock has a free GPIO I can use for this. And then I’m also not sure if the library needs interrupts or not.

I’ll update here if I find anything. If you have any ideas, please let me know.

4

Following your need of an SDI interface module I put it on the list of new WisBlock modules for this year. But I cannot promise any availability date. We are planning at least 3 events this year where we will present new WisBlock modules.

5

At this point I need to find a way to test the viability of using the WisBlock to read out SDI-12 soil moisture probes. It needs to happen asap, as it influences business decisions.

We can’t wait for RAK to release a new comms module every time we want to do something new/custom. In this case the best is to find a way to directly interface with the WisBlock without a connectivity module. I’ll search for the docs and see if there is a GPIO which can be used.

6

I understand your problem.

If I might recommend something, look at

  • the RAK1920, which has several GPIO’s, SPI and I2C exposed on the Click! connector.
    image
  • or the 5804 which has all available GPIO’s, I2C, Serial and SPI exposed on a small connector. It comes with a matching connector and cable to connect external devices.
    image
1 Like
7

Yes, that is a good idea. What do you think about the J10 and J11 headers on the base board? I see J11 has a free GPIO on pin 2. That might work. I’m still looking through the documentation of the WisBlock to figure out exactly how to use these pin from Arduino.

8

IO1 on J11 would be available to use.

We know about the confusing different naming of GPIO’s on the RAK5005-O and the RAK4631.
In the next release of the Arduino BSP we will have all RAK5005-O GPIO’s predefined and linked to the correct GPIO numbers of the RAK4631.

For now you can use this list as a start:

	/*
 * WisBlock Base GPIO definitions
 */
	static const uint8_t WB_IO1 = 17;	   // SLOT_A SLOT_B
	static const uint8_t WB_IO2 = 34;	   // SLOT_A SLOT_B
	static const uint8_t WB_IO3 = 21;	   // SLOT_C
	static const uint8_t WB_IO4 = 4;	   // SLOT_C
	static const uint8_t WB_IO5 = 9;	   // SLOT_D
	static const uint8_t WB_IO6 = 10;	   // SLOT_D
	static const uint8_t WB_SW1 = 33;	   // IO_SLOT
	static const uint8_t WB_A0 = 5;		   // IO_SLOT
	static const uint8_t WB_A1 = 31;	   // IO_SLOT
	static const uint8_t WB_I2C1_SDA = 13; // SENSOR_SLOT IO_SLOT
	static const uint8_t WB_I2C1_SCL = 14; // SENSOR_SLOT IO_SLOT
	static const uint8_t WB_I2C2_SDA = 24; // IO_SLOT
	static const uint8_t WB_I2C2_SCL = 25; // IO_SLOT
	static const uint8_t WB_SPI_CS = 26;   // IO_SLOT
	static const uint8_t WB_SPI_CLK = 3;   // IO_SLOT
	static const uint8_t WB_SPI_MISO = 29; // IO_SLOT
	static const uint8_t WB_SPI_MOSI = 30; // IO_SLOT

WB_IOx refers to the IO name used on the RAK5005-O and on the modules.

9

I was able to get SDI-12 working on the Wisblock using SoftwareSerial. The ArduinoSDI12 library didn’t work, even after I hacked it to use the micros() timer for timing.

SoftwareSerial does not support any other serial mode than SERIAL_8N1. But SDI-12 uses SERIAL_7E1. I therefore manually add a parity bit to every byte before I transmit, and I ignore the parity bit on rx.

Example code below:

#include <SoftwareSerial.h>

SoftwareSerial sdi12rx(17, -1, true);
SoftwareSerial sdi12tx(-1, 17, true);

uint8_t command[] = "?I!";

uint8_t rxBuffer[64];

void setup() {
  Serial.begin(57600);
  while(!Serial);
  Serial.println("Startup");

  addParityBits(command, sizeof(command)-1);
}

void loop() {
  
  Serial.println("loop");

  Serial.print("Request: ");
  for(int i=0; i<sizeof(command); i++) {
    if(command[i] < 0x10) Serial.print("0");
    Serial.print(command[i], HEX);
    Serial.print(" ");
  }
  Serial.println();
  
  pinMode(17, OUTPUT);
  digitalWrite(17, HIGH);
  delay(12);
  digitalWrite(17, LOW);
  delay(9);
  
  sdi12tx.begin(1200);
  sdi12tx.write(command, sizeof(command)-1);

  delay(6);
  sdi12tx.end();
  pinMode(17, INPUT_PULLDOWN);
  
  sdi12rx.begin(1200);
  sdi12rx.setTimeout(2000);

  Serial.print("Response: ");
  unsigned long startTime = millis();
  int bytesRead = 0;
  while(millis()-startTime < 2000) {
    if(sdi12rx.available()) {
      uint8_t response = sdi12rx.read() & 0b01111111; // ignore parity bit
      rxBuffer[bytesRead++] = response;
      if(response == 0x0A) {
        break;
      }
    }
  }

  delay(6);
  sdi12rx.end();
  while(sdi12rx.available()) sdi12rx.read();
  
  pinMode(17, INPUT_PULLDOWN);
  Serial.println("RX closed");

  Serial.write(rxBuffer, bytesRead);

  delay(2000);
}

void addParityBits(uint8_t* dataBuffer, size_t bufferLength) {
  for(int i=0; i<bufferLength; i++) {
    uint8_t parity = calcParityBit(dataBuffer[i]);
    if(parity) {
      dataBuffer[i] = dataBuffer[i] | 0b10000000;
    } else {
      dataBuffer[i] = dataBuffer[i] & 0b01111111;
    }
  }
}

char calcParityBit (unsigned char v)
{
    return (0x6996u >> ((v ^ (v >> 4)) & 0xf)) & 1;
}
10

@jpmeijers
Congratulations.
If we ever make a SDI-12 module, might we use your patched SoftwareSerial library?

11

I’m using the standard SoftwareSerial library without any changed. All the required changes to do SERIAL_7E1 are done in the sketch posted above.

If you ever make an SDI-12 module, I would suggest you stick to HardwareSerial where one has native Serial Modes.

12

I know this is pretty old, but I would like to add a vote to having an SDI-12 module - would open up and simplify a lot of possibilities with sensors

13

Under development. Will come this year.

1 Like