How to read pH value

Question

I am trying to read the pH value from a analog pH meter, SEN-01454. From the source code I found, voltage maps to pH value. This is the code:

pHArray[pHArrayIndex++]=analogRead(SensorPin);
 if(pHArrayIndex==ArrayLenth)pHArrayIndex=0;
 voltage = avergearray(pHArray, ArrayLenth)*5.0/1024;
 pHValue = 3.5*voltage+Offset;
 samplingTime=millis();

But then the value is not correct. So how do i actually do it.

The example code from Wiki page for product.

• RSM: What value do you expect?
• Dinesh Sekar: the value of the liquid
• RSM: ok a bit more specific, what liquid are you testing. Do you know what that liquids' pH is, this is of use if you are calibrating it. If you are testing a liquid and don't know its pH before testing you might actually be getting the right value.
• Dinesh Sekar: Sodium Hydroxide which is pH value of 12.
• RSM: and the value you are getting?

Answer 1

This is SOME of the code. We are missing the avergearray() function.. I suspect you're taking one reading and averaging it with both old & future ones, but this code clearly is meant to sit in a loop..

From another source, I got this:

/*
# This sample codes is for testing the pH meter V1.0.
 # Editor : YouYou
 # Date : 2013年10月12日
 # Ver : 0.1
 # Product: pH meter
 # SKU : SEN0161
*/
#define SensorPin 0 //pH meter Analog output to Arduino Analog Input 0
unsigned long int avgValue; //Store the average value of the sensor feedback
float b;
int buf[10],temp;
void setup()
{
 pinMode(13,OUTPUT); 
 Serial.begin(9600); 
 Serial.println("Ready"); //Test the serial monitor
}
void loop()
{
 for(int i=0;i<10;i++) //Get 10 sample value from the sensor for smooth the value
 { 
 buf[i]=analogRead(SensorPin);
 delay(10);
 }
 for(int i=0;i<9;i++) //sort the analog from small to large
 {
 for(int j=i+1;j<10;j++)
 {
 if(buf[i]>buf[j])
 {
 temp=buf[i];
 buf[i]=buf[j];
 buf[j]=temp;
 }
 }
 }
 avgValue=0;
 for(int i=2;i<8;i++) //take the average value of 6 center sample
 avgValue+=buf[i];
 float phValue=(float)avgValue*5.0/1024/6; //convert the analog into millivolt
 phValue=3.5*phValue; //convert the millivolt into pH value
 Serial.print(" pH:"); 
 Serial.print(phValue,2);
 Serial.println(" ");
 digitalWrite(13, HIGH); 
 delay(800);
 digitalWrite(13, LOW); 
}

which reads in the array first and then averages it. Is this what your code does? If so, what sort of errors are you seeing?

• Dinesh Sekar: There is no error. But i can't get the correct value of the pH
• Mark Williams: So what values do you get instead? And, with respect, there probably is an error - or it would work!