Understanding pH code

Projects Programming
1

Hello guys, I'm a newbie and I'm currently working on a project to build a pH meter. I read other posts about pH meter, but I was not able to understand some parts of the code. The code is working, no problem with that, I tested two buffer solutions (pH=4,0 and pH=7,0) and they retrieved a perfect match in the serial monitor. I just don't want to use a code without knowing how it works.

Source of the code and more informations on how pH meters work: https://www.botshop.co.za/how-to-use-a-ph-probe-and-sensor/

float calibration = 0.00;       // change this value to calibrate
const int analogInPin = A0; // pin which the sensor is connected
int sensorValue = 0;          // there's no further reference to this
unsigned long int avgValue; 
float b;                            // there's no further reference to this
int buf[10],temp;             // what's this temp for?
void setup() {
 Serial.begin(9600);
}
 void loop() {
 for(int i=0;i<10;i++)     // get 10 sample value from the sensor for smooth the value
 { 
 buf[i]=analogRead(analogInPin);
 delay(30);
 }
 for(int i=0;i<9;i++)      // sort the analog from small to large(?) How come?
 {
 for(int j=i+1;j<10;j++)
 {
 if(buf[i]>buf[j])
 {
 temp=buf[i];               // these equations work as a reset to the values?
 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 pHVol=(float)avgValue*5.0/1024/6;           // convert the analog into millivolt
 float phValue = -5.70 * pHVol + calibration;      // this comes from a linear function
 Serial.print("sensor = ");
 Serial.println(phValue);
 delay(500);
}

Thanks so much for your attention.

2

(deleted)

3

Assuming that the questions in the code are the ones that you should have asked in the post , this comment in the code explains why the data must be sorted:

// take the average value of 6 center samples

This is a noise filter approach, related to the median filter.

4

spycatcher2k:
Which SPECIFIC lines / blocks do you not understand?

Sorry, I made my questions in the comments within the code I posted. I don't see a reason to declare int sensorValue = 0, if it's not been used after, and so does float b. I suppose this code is a part of some original code that someone may have cut, am I right?

My doubts remain on these constructions, (what they do?):

for(int i=0;i<9;i++)      
 {
 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;
5

jremington:
Assuming that the questions in the code are the ones that you should have asked in the post , this comment in the code explains why the data must be sorted:
This is a noise filter approach, related to the median filter.

Thanks for your answear jremington, I'll search this subject. And sorry about the incorrect posting.

6

My doubts remain on these constructions

Simple sort of the data.

If variables are declared in the code but never used, remove those declarations.