How to Use Gravity TDS Sensor [Bill Ludwig]: Examples, Pinouts, and Specs

The Gravity TDS Sensor, manufactured by Seeed (Part ID: Gravity TDS Sensor), is a specialized sensor designed to measure the Total Dissolved Solids (TDS) in a liquid. TDS is a critical parameter for assessing water quality, as it indicates the concentration of dissolved ions, such as salts, minerals, and metals, in the liquid. This sensor provides an easy and reliable way to monitor water quality in real-time.

• Water quality monitoring in aquariums, hydroponics, and aquaculture
• Environmental water testing in rivers, lakes, and reservoirs
• Industrial water treatment systems
• Educational and research projects involving water analysis

The Gravity TDS Sensor is designed for ease of use and compatibility with microcontrollers like Arduino. Below are its key technical details:

The Gravity TDS Sensor has a 3-pin interface for easy connection to microcontrollers. Below is the pinout:

1. Connect the Sensor to a Microcontroller:

   • Connect the VCC pin to the 5V (or 3.3V) power supply of the microcontroller.
   • Connect the GND pin to the ground (GND) of the microcontroller.
   • Connect the AOUT pin to an analog input pin on the microcontroller (e.g., A0 on an Arduino UNO).

2. Calibrate the Sensor:

   • Immerse the probe in a standard solution with a known TDS value (e.g., 342 ppm).
   • Adjust the calibration potentiometer on the sensor module until the output matches the known TDS value.

3. Write and Upload Code:

   • Use the following Arduino code to read and display TDS values:

// Include necessary libraries
// No additional libraries are required for basic TDS measurement

// Define the analog pin connected to the TDS sensor
const int TDS_PIN = A0;

// Define the voltage reference of the microcontroller (5.0V for Arduino UNO)
const float VREF = 5.0;

// Define the TDS factor (calibration constant, typically 0.5 for this sensor)
const float TDS_FACTOR = 0.5;

void setup() {
  Serial.begin(9600); // Initialize serial communication
  pinMode(TDS_PIN, INPUT); // Set the TDS pin as input
}

void loop() {
  int analogValue = analogRead(TDS_PIN); // Read the analog value from the sensor
  float voltage = analogValue * (VREF / 1024.0); // Convert to voltage
  float tdsValue = (voltage / TDS_FACTOR) * 1000; // Calculate TDS in ppm

  // Print the TDS value to the Serial Monitor
  Serial.print("TDS Value: ");
  Serial.print(tdsValue);
  Serial.println(" ppm");

  delay(1000); // Wait for 1 second before the next reading
}

• Temperature Compensation: The sensor includes basic temperature compensation, but for highly accurate measurements, use an external temperature sensor to adjust the TDS calculation.
• Probe Maintenance: Rinse the probe with distilled water after each use to prevent residue buildup and ensure accurate readings.
• Avoid Air Bubbles: Ensure the probe is fully submerged in the liquid without air bubbles, as they can affect the measurement.
• Calibration: Regularly calibrate the sensor using a standard TDS solution to maintain accuracy.

1. Inaccurate Readings:

   • Cause: The sensor is not calibrated.
   • Solution: Calibrate the sensor using a standard TDS solution.

2. No Output Signal:

   • Cause: Incorrect wiring or loose connections.
   • Solution: Verify the connections to the VCC, GND, and AOUT pins.

3. Fluctuating Readings:

   • Cause: Air bubbles or unstable liquid conditions.
   • Solution: Ensure the probe is fully submerged and the liquid is stable.

4. Sensor Not Responding:

   • Cause: Damaged probe or module.
   • Solution: Inspect the probe and module for physical damage and replace if necessary.

Q: Can the Gravity TDS Sensor measure salinity?
A: While the sensor measures TDS, which includes dissolved salts, it is not specifically designed for salinity measurement. For precise salinity readings, use a dedicated salinity sensor.

Q: Is the sensor compatible with Raspberry Pi?
A: Yes, the sensor can be used with Raspberry Pi by connecting it to an analog-to-digital converter (ADC), as Raspberry Pi lacks native analog input pins.

Q: How often should the sensor be calibrated?
A: Calibration frequency depends on usage. For critical applications, calibrate before each use. For general use, calibrate monthly or as needed.

Q: Can the sensor be used in hot liquids?
A: The sensor is designed for liquids within a temperature range of 10°C to 40°C. Using it outside this range may damage the probe or affect accuracy.