Resistance Measurement with Arduino

Techniques for measuring variable resistances using voltage dividers

Why Measure Resistance?

Resistive Sensors

Key Applications

  • Light-dependent resistors (LDR)
  • Thermistors for temperature sensing
  • Flex sensors
  • Potentiometers
  • Strain gauges

Measurement Principle

Voltage Divider Circuit

Voltage divider schematic

Vout = Vin × (R2 / (R1 + R2))

Arduino Implementation

Breadboard setup

Analog input measures voltage between resistors

Implementation Code


const int sensorPin = A0;
const int Rc = 1500;  // Calibration resistor value

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

void loop() {
  int raw = analogRead(sensorPin);
  float voltage = raw * (5.0 / 1023.0);
  float Rsensor = Rc * (1023.0 / raw - 1);
  
  Serial.print("Resistance: ");
  Serial.println(Rsensor);
  delay(1000);
}
                    

const int sensorPin = A0;
const long Rc = 1500L;  // Calibration resistor value

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

void loop() {
  int raw = analogRead(sensorPin);
  long Rsensor = (1024L * Rc) / raw - Rc;
  
  Serial.print("Resistance: ");
  Serial.println(Rsensor);
  delay(1000);
}

Choosing Calibration Resistor

Selection Guidelines

Sensor Range Recommended Rc
100Ω - 1kΩ 1kΩ
1kΩ - 10kΩ 4.7kΩ
10kΩ - 100kΩ 47kΩ

Current Considerations

  • Max current at 5V: 5mA
  • Power dissipation: 0.125W max
  • ADC input impedance: 10MΩ

Resistance Calculator



Calculated Resistance: