New from today: soil moisture sensor

Hello, everyone,

Today I would like to introduce you to a new sensor that we have in our shop. Our capacitive hygrometer V1.2

This module works capacitively, i.e. in contrast to the predecessor model there is no corrosion by galvanic processes. The output of this sensor is analog, i.e. although it supports 3.3V controllers, it cannot be read out by a Raspberry, which has no analog input. In principle, this sensor module is not only suitable for measuring the humidity in substrate, but also for displaying a fill level. Before we use the sensor productively our sketch has to be calibrated to the respective values.

For our application example we use a NanoV3. And a glass of water instead of a flower pot, because the humidity of the substrate cannot be changed as easily as the level of a glass. Libarys are not required.

Pinout:

We start with the simplest commissioning, the analogreadserial example which is already integrated in the IDE: Examples -> Basics ->AnalogReadSerial

and receive the following edition in the serial monitor:

It looks a little more appealing in the serial plotter, but is still not ideal:

We use the smoothing tutorial on arduino.cc, here the code:

/*
  Smoothing

  created 22 Apr 2007
  by David A. Mellis  <dam@mellis.org>
  modified 9 Apr 2012
  by Tom Igoe

  This example code is in the public domain.

  http://www.arduino.cc/en/Tutorial/Smoothing
*/

const int numReadings = 10;

int readings[numReadings];      // the readings from the analog input
int readIndex = 0;              // the index of the current reading
int total = 0;                  // the running total
int average = 0;                // the average

int inputPin = A0;

void setup() {

  Serial.begin(9600);

  for (int thisReading = 0; thisReading < numReadings; thisReading++) {
    readings[thisReading] = 0;
  }
}

void loop() {
  // subtract the last reading:
  total = total - readings[readIndex];
  // read from the sensor:
  readings[readIndex] = analogRead(inputPin);
  // add the reading to the total:
  total = total + readings[readIndex];
  // advance to the next position in the array:
  readIndex = readIndex + 1;

  // if we're at the end of the array...
  if (readIndex >= numReadings) {
    // ...wrap around to the beginning:
    readIndex = 0;
  }

  // calculate the average:
  average = total / numReadings;
  Serial.println(average);
  delay(1);        // delay in between reads for stability
}

After we have uploaded the code, the optical edition is a little more pleasant:

So we find that the empty glass gives values around 792. Thus we have determined the highest value. Now we determine the lowest value by immersing our sensor in water to a height you specify.

The immersion depth, i.e. the height of the level in the glass/substrate must always remain the same for comparisons, we decided to use the point of v1.2 as a marker. And get the following values:

The full glass delivers approx. 419, i.e. we are in a range of 792 - 419. Please make sure to perform this calibration in the medium you want to use later, as the values vary depending on the substrate.

Because this sensor is so versatile, different substrates are possible, plants have different preferences and we can not estimate your scale, we provide here code that we have already used in our  Alcotester  have shown:

if (average >= 0 and average <= 400) {
    state = "Sensor defekt?";
  }
  else if (average >= 400 and average <= 500) {
    state = "Durst!";
  }
  else if (average >= 500 and average <= 649) {
    state = "Feucht!";
  }
  else if (average >= 650 and average <= 800) {
    state = "Patschnass!";

There is a housing for printing yourself, you will find the required files here.

Have fun trying and experimenting, maybe you will find a loyal reader who wants to make a smart drinking glass, which shows the bartender the level of his guests. :) Until the next post