/*
TDS
*/


#define tds_pin 36 // tds is connected to GPIO 36 (Analog ADC0)  VP
 
int sensorValue = 0;
float tdsValue = 0;
float Voltage = 0;
 
void setup() {
    Serial.begin(9600);
}
void loop() {
    sensorValue = analogRead(tds_pin);
    Voltage = sensorValue*5/1024.0; //Convert analog reading to Voltage
    //tdsValue=(133.42/Voltage*Voltage*Voltage - 255.86*Voltage*Voltage + 857.39*Voltage)*0.5; //Convert voltage value to TDS value
    //must be abs
    tdsValue=abs(133.42/Voltage*Voltage*Voltage - 255.86*Voltage*Voltage + 857.39*Voltage)*0.5; //Convert voltage value to TDS value
    Serial.print("TDS Value = "); 
    Serial.print(tdsValue);
    Serial.println(" ppm");
    delay(1000);
}