Hello,
I guess it is the same as Vinduino :
with their test code:
// This program tests 3 soil sensor inputs and prints bias caused by galvanic effects
// Copyright (C) 2015, Reinier van der Lee
// www.vanderleevineyard.com
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// any later version.
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
#include <math.h> // Conversion equation from resistance to %
// Setting up format for reading 3 soil sensors
#define NUM_READS 10 // Number of sensor reads for filtering
long buffer[NUM_READS];
int index;
typedef struct { // Structure to be used in percentage and resistance values matrix to be filtered (have to be in pairs)
int moisture;
long resistance;
} values;
const long knownResistor = 1500; // Constant value of known resistor in Ohms
int supplyVoltage; // Measured supply voltage
int sensorVoltage; // Measured sensor voltage
values valueOf[NUM_READS]; // Calculated moisture percentages and resistances to be sorted and filtered
int i; // Simple index variable
void setup() {
// initialize serial communications at 9600 bps:
Serial.begin(115200);
// initialize the digital pins as an output.
// Pin 6,7 is for sensor 1
pinMode(6, OUTPUT);
pinMode(7, OUTPUT);
}
void loop() {
measure(1,6,7,1);
Serial.print ("\t");
Serial.println (average());
long read1 = average();
measure(1,7,6,0);
Serial.print ("\t");
Serial.println (average());
long read2= average();
long sensor1 = (read1 + read2)/2;
Serial.print ("resistance bias =" );
Serial.println (read1-read2);
Serial.print ("sensor bias compensated value = ");
Serial.println (sensor1);
Serial.println ();
delay (3000);
}
void measure (int sensor, int phase_b, int phase_a, int analog_input)
{
// read sensor, filter, and calculate resistance value
// Noise filter: median filter
for (i=0; i<NUM_READS; i++) {
// Read 1 pair of voltage values
digitalWrite(phase_a, HIGH); // set the voltage supply on
delayMicroseconds(25);
supplyVoltage = analogRead(analog_input); // read the supply voltage
delayMicroseconds(25);
digitalWrite(phase_a, LOW); // set the voltage supply off
delay(1);
digitalWrite(phase_b, HIGH); // set the voltage supply on
delayMicroseconds(25);
sensorVoltage = analogRead(analog_input); // read the sensor voltage
delayMicroseconds(25);
digitalWrite(phase_b, LOW); // set the voltage supply off
// Calculate resistance
// the 0.5 add-term is used to round to the nearest integer
// Tip: no need to transform 0-1023 voltage value to 0-5 range, due to following fraction
long resistance = (knownResistor * (supplyVoltage - sensorVoltage ) / sensorVoltage)-457 ;
delay(1);
addReading(resistance);
Serial.print (resistance);
Serial.print ("\t");
}
}
// Averaging algorithm
void addReading(long resistance){
buffer[index] = resistance;
index++;
if (index >= NUM_READS) index = 0;
}
long average(){
long sum = 0;
for (int i = 0; i < NUM_READS; i++){
sum += buffer[i];
}
return (long)(sum / NUM_READS);
}
and my hall of fame and shame of sensors I've tried :
