Is my circuit board in the Analog pH Meter kit defective?

This article is supposed to check whether the pH sensor circuit board in the two PH meter kits: Analog pH Meter Pro and Analog pH Meter Kit.

Some users found very strange readings of their ph liquor even after they follow the wiki steps, i.e. after Zero Adjustment. It might be the circuit board is defective. Now let's take a look at how to confirm it, very simple.

Requirments:

Steps
NOTE: Make sure the Arduino controller can suply good 5V voltage to the board.

STEP 1 If you have checked the 5V voltage supply from Arduino was no problem. Then short circuit the circuit board input with a metal tweezers( or a wire) to simulate that the PH=7.0 and the voltage reading should be 2.0V.

STEP 2 Connect the circuit board to Arduino Uno on A0. (if you use Leonardo, note if the switch for buttons on board was ON)

STEP 3 Upload the sample code on the wiki, or copy from here.
 

Code: Select all#define SensorPin A0            //pH meter Analog output to Arduino Analog Input 0
#define Offset 0.00            //deviation compensate
#define LED 13
#define samplingInterval 20
#define printInterval 800
#define ArrayLenth  40    //times of collection
int pHArray[ArrayLenth];   //Store the average value of the sensor feedback
int pHArrayIndex=0;    
void setup(void)
{
  pinMode(LED,OUTPUT);  
  Serial.begin(9600);  
  Serial.println("pH meter experiment!");    //Test the serial monitor
}
void loop(void)
{
  static unsigned long samplingTime = millis();
  static unsigned long printTime = millis();
  static float pHValue,voltage;
  if(millis()-samplingTime > samplingInterval)
  {
      pHArray[pHArrayIndex++]=analogRead(SensorPin);
      if(pHArrayIndex==ArrayLenth)pHArrayIndex=0;
      voltage = avergearray(pHArray, ArrayLenth)*5.0/1024;
      pHValue = 3.5*voltage+Offset;
      samplingTime=millis();
  }
  if(millis() - printTime > printInterval)   //Every 800 milliseconds, print a numerical, convert the state of the LED indicator
  {
   Serial.print("Voltage:");
        Serial.print(voltage,2);
        Serial.print("    pH value: ");
   Serial.println(pHValue,2);
        digitalWrite(LED,digitalRead(LED)^1);
        printTime=millis();
  }
}
double avergearray(int* arr, int number){
  int i;
  int max,min;
  double avg;
  long amount=0;
  if(number<=0){
    Serial.println("Error number for the array to avraging!/n");
    return 0;
  }
  if(number<5){   //less than 5, calculated directly statistics
    for(i=0;i<number;i++){
      amount+=arr[i];
    }
    avg = amount/number;
    return avg;
  }else{
    if(arr[0]<arr[1]){
      min = arr[0];max=arr[1];
    }
    else{
      min=arr[1];max=arr[0];
    }
    for(i=2;i<number;i++){
      if(arr[i]<min){
        amount+=min;        //arr<min
        min=arr[i];
      }else {
        if(arr[i]>max){
          amount+=max;    //arr>max
          max=arr[i];
        }else{
          amount+=arr[i]; //min<=arr<=max
        }
      }//if
    }//for
    avg = (double)amount/(number-2);
  }//if
  return avg;
}

STEP 4 Open the serial monitor, choose "9600" baud rate. Then if your readings are:"2.0V, PH=7.0(6.9~7.1)" like below, it proves that the board is good. Or if your readings are not stable or not around 2.0V, ph=7.0, then the circuit board is defective.