Overview

The SEN0244 (DFRobot Gravity Analog TDS Sensor / Meter) is an analog water quality sensor designed for hydroponics, aquarium monitoring, swimming pool chemistry, and drinking water testing. It measures Total Dissolved Solids (TDS)—the total concentration of dissolved inorganic salts (calcium, magnesium, potassium, sodium) and organic matter expressed in Parts Per Million (PPM) or milligrams per liter (mg/L).

Built around an AC excitation signal generator circuit (which prevents electrochemical probe polarization and extends probe lifespan), the SEN0244 outputs a continuous analog voltage (0V…2.3V0\text{V} \dots 2.3\text{V}) across a 3-pin DFRobot Gravity connector.

Quick reference

Operating voltage (VCC)3.3 V to 5.5 V DC (3.3 V or 5.0 V nominal)
Output voltage (A)0.0V0.0\text{V} to 2.3V2.3\text{V} analog DC voltage
Measurement Range0 to 1000 PPM0\text{ to }1000\text{ PPM} (mg/Lmg/L)
Measurement Accuracy±10% F.S.\pm 10\%\ \text{F.S.} (at 25∘C25^\circ\text{C})
Probe ExcitationAC square wave signal (anti-polarization)
Waterproof Probe2-needle black submersible IP68 probe (60 cm60\text{ cm} cable)
Operating current3.0 mA…6.0 mA3.0\text{ mA} \dots 6.0\text{ mA}

Pinout

Breakout board 3-pin 0.1" (2.54 mm) DFRobot Gravity connector:

PinNameTypeDescription
1 (A)SIGNALAnalog Output0V…2.3V0\text{V} \dots 2.3\text{V} analog voltage output
2 (+)VCCPowerSupply power input (+3.3 V to +5.5 V DC)
3 (-)GNDPowerGround reference (0 V)
2-Pin TerminalPROBEAnalog Input2-pin JST connector for waterproof TDS probe

Specifications

ParameterSymbolMinTypMaxUnitConditions
Supply VoltageVCCV_{CC}3.35.05.5VDC
Active Supply CurrentICCI_{CC}3.04.56.0mAActive measurement
Output Voltage RangeVoutV_{out}0.0—2.3V0…1000 PPM0 \dots 1000\text{ PPM} range
TDS Measurement RangeTDSTDS0—1000PPMParts Per Million (mg/L)
TDS Full-Scale AccuracyAccTDSAcc_{TDS}-10.0±10.0\pm 10.0+10.0% F.S.Twater=25∘CT_{water} = 25^\circ\text{C}
Probe Cable LengthLenLen—60—cmSubmersible probe cable

Temperature Compensation & TDS Math

TDS conductivity is highly temperature-dependent (+2%/∘C+2\%/^\circ\text{C} increase per degree Celsius).

  1. Calculate Temperature Compensation Factor (TCFTCF):

TCF=1.0+0.02×(Twater−25.0)TCF = 1.0 + 0.02 \times (T_{water} - 25.0)

  1. Calculate Compensated Voltage (VcompV_{comp}):

Vcomp=VrawTCFV_{comp} = \frac{V_{raw}}{TCF}

  1. Calculate TDS Value (PPM):

TDS (PPM)=(133.42⋅Vcomp3−255.86⋅Vcomp2+857.39⋅Vcomp)×0.5\text{TDS (PPM)} = \left( 133.42 \cdot V_{comp}^3 - 255.86 \cdot V_{comp}^2 + 857.39 \cdot V_{comp} \right) \times 0.5

Wiring

SEN0244 Pin→Arduino UnoESP32Notes
VCC (+)5V / 3.3V3.3VPower rail
GND (-)GNDGNDSystem ground
A (SIGNAL)Analog Pin A0VP / GPIO36Analog voltage output

Example (Arduino Code with Temp Compensation)

cpp
#define TdsSensorPin A0
#define VREF 5.0      // Analog reference voltage (5.0V or 3.3V)
#define SCOUNT  30    // Sum sample count for median filtering

int analogBuffer[SCOUNT];
int analogBufferTemp[SCOUNT];
int analogBufferIndex = 0, copyIndex = 0;
float averageVoltage = 0, tdsValue = 0, temperature = 25.0; // Water temp 25°C

void setup() {
  Serial.begin(115200);
  pinMode(TdsSensorPin, INPUT);
}

void loop() {
  static unsigned long sampleTimepoint = millis();
  if (millis() - sampleTimepoint > 40U) {
    sampleTimepoint = millis();
    analogBuffer[analogBufferIndex] = analogRead(TdsSensorPin);
    analogBufferIndex++;
    if (analogBufferIndex == SCOUNT) analogBufferIndex = 0;
  }

  static unsigned long printTimepoint = millis();
  if (millis() - printTimepoint > 800U) {
    printTimepoint = millis();
    for (copyIndex = 0; copyIndex < SCOUNT; copyIndex++) {
      analogBufferTemp[copyIndex] = analogBuffer[copyIndex];
    }
    averageVoltage = getMedianNum(analogBufferTemp, SCOUNT) * (float)VREF / 1024.0;
    
    // Temperature compensation formula
    float compensationCoefficient = 1.0 + 0.02 * (temperature - 25.0);
    float compensationVoltage = averageVoltage / compensationCoefficient;
    
    // Convert voltage to TDS value
    tdsValue = (133.42 * pow(compensationVoltage, 3) - 255.86 * pow(compensationVoltage, 2) + 857.39 * compensationVoltage) * 0.5;

    Serial.print("Voltage: "); Serial.print(averageVoltage, 2); Serial.print(" V | ");
    Serial.print("TDS Value: "); Serial.print(tdsValue, 0); Serial.println(" PPM");
  }
}

int getMedianNum(int bArray[], int iFilterLen) {
  int i, j, bTemp;
  for (j = 0; j < iFilterLen - 1; j++) {
    for (i = 0; i < iFilterLen - j - 1; i++) {
      if (bArray[i] > bArray[i + 1]) {
        bTemp = bArray[i];
        bArray[i] = bArray[i + 1];
        bArray[i + 1] = bTemp;
      }
    }
  }
  return bArray[(iFilterLen - 1) / 2];
}

Common mistakes

  • Submerging the entire probe connector: Only the black needle tip of the TDS probe is IP68 waterproof. The 2-pin JST connector cap and signal adapter PCB must remain dry.
  • Forgetting temperature compensation: Reading 20∘C20^\circ\text{C} water without temperature compensation introduces a −10%-10\% error in calculated PPM.

Notes

  • TDS vs EC (Electrical Conductivity): 1 ms/cm EC≈500 PPM TDS1\text{ ms/cm EC} \approx 500\text{ PPM TDS} (using standard 0.5 conversion factor).

Assets & downloads