Grade 9 · From USB to Field System: ESP32 water quality

Measure electrical conductivity

Follow the student handout to build, test and document this stage of the water-quality system.

Prepared lesson material. Start this task when your teacher introduces it; it is not currently assigned homework.

For this lesson

Open student handout (Word)All Grade 9 handouts →

3 pages · Use the handout for the complete instructions, examples and response spaces.

Read the handout text online

For diagrams, visual examples and the full layout, open the handout above.

Lesson 7: Conductivity and Analog Input

EC wiring, library installation, and sample comparison

Grade 9 MYP Design | From USB to Field System

Name: __________________

Class / team: __________________

Date: __________________

Today’s goals • Read raw ADC and voltage from the EC board. • Use the DFRobot_EC library with temperature compensation. • Interpret units cautiously.

Key vocabulary

Term	Working definition
conductivity
ion
analog
ADC
millivolt
mS/cm
µS/cm
calibration
temperature compensation

1. Wiring

ESP32.3V3 -> EC_BOARD.VCCESP32.GND -> EC_BOARD.GNDEC_BOARD.AO -> ESP32.GPIO1EC_BOARD.T1 -> NOT CONNECTED

2. Install DFRobot_EC

Open https://github.com/DFRobot/DFRobot_EC

Choose Code → Download ZIP.

In Arduino IDE, choose Sketch → Include Library → Add .ZIP Library.

If installation fails, unzip and place a folder named DFRobot_EC in Documents/Arduino/libraries so DFRobot_EC.h is directly inside it.

3. Test code

#include <OneWire.h>#include <DallasTemperature.h>#include <DFRobot_EC.h>#include <EEPROM.h>#define DS18B20_PIN 4#define EC_PIN 1OneWire oneWire(DS18B20_PIN);DallasTemperature tempSensor(&oneWire);DFRobot_EC ec;void setup() { Serial.begin(115200); EEPROM.begin(32); tempSensor.begin(); ec.begin(); analogReadResolution(12); analogSetPinAttenuation(EC_PIN, ADC_11db); Serial.println("temp_C,ec_raw,ec_mV,ec_mS_cm,ec_uS_cm");}void loop() { tempSensor.requestTemperatures(); float tempC = tempSensor.getTempCByIndex(0); int raw = analogRead(EC_PIN); float mV = raw * (3300.0 / 4095.0); float mS = ec.readEC(mV, tempC); ec.calibration(mV, tempC); Serial.print(tempC, 2); Serial.print(','); Serial.print(raw); Serial.print(','); Serial.print(mV, 1); Serial.print(','); Serial.print(mS, 3); Serial.print(','); Serial.println(mS * 1000.0, 1); delay(2000);}

4. Sample comparison

Sample	Trial 1 mS/cm	Trial 2	Trial 3	Mean	Prediction supported?
Filtered water
Tap water
Weak salt solution

5. Interpret the units

Convert 1.413 mS/cm to µS/cm: __________________________

Why should today’s EC values be described as estimated or relative?

________________________________________________________________________________________________________________

Probe care Rinse between samples. Keep immersion depth and waiting time consistent. Do not let salt solution dry on the probe.