ph metre problem

I use this ph metre module 4502c. The problem is that the values ​​that I get constantly change i do not get a fixed value

19:51:10.796 -> Measure: 538 Voltage: 2.627 PH: 6.295
19:51:12.808 -> Measure: 964 Voltage: 4.707 PH: -5.261
19:51:14.848 -> Measure: 1023 Voltage: 4.995 PH: -6.862
19:51:16.856 -> Measure: 1009 Voltage: 4.927 PH: -6.482
19:51:18.859 -> Measure: 713 Voltage: 3.481 PH: 1.548
19:51:20.871 -> Measure: 195 Voltage: 0.952 PH: 15.599
19:51:22.920 -> Measure: 203 Voltage: 0.991 PH: 15.382
19:51:24.932 -> Measure: 190 Voltage: 0.928 PH: 15.735
19:51:26.945 -> Measure: 221 Voltage: 1.079 PH: 14.894
19:51:28.953 -> Measure: 261 Voltage: 1.274 PH: 13.809
19:51:30.993 -> Measure: 630 Voltage: 3.076 PH: 3.799

i use this progrm

int ph_pin = A7; //This is the pin number connected to Po

void setup() {
Serial.begin(9600);
}

void loop() {
int measure = analogRead(ph_pin);
Serial.print("Measure: ");
Serial.print(measure);

double voltage = 5 / 1024.0 * measure; //classic digital to voltage conversion
Serial.print("\tVoltage: ");
Serial.print(voltage, 3);

// PH_step = (voltage@PH7 - voltage@PH4) / (PH7 - PH4)
// PH_probe = PH7 - ((voltage@PH7 - voltage@probe) / PH_step)
float Po = 7 + ((2.5 - voltage) / 0.18);
Serial.print("\tPH: ");
Serial.print(Po, 3);

Serial.println("");
delay(2000);
}

can any one help me please

Did you connect the grounds?

yesss
:frowning:

Check the continuity of all connections. It appears that you have a "floating input".

Post a wiring diagram and a link to the pH meter module or operating manual.