Measuring Voltage with the Arduino

The Arduino is a versatile microcontroller capable of measuring voltage using its built-in analog-to-digital converter (ADC). This capability is essential for applications like monitoring battery levels, sensing input signals, and measuring sensor outputs. This tutorial will guide you through the process of measuring voltage with an Arduino.

---

What You Will Need

1. Arduino Board (e.g., Uno, Mega, Nano)
2. Voltage Divider (if measuring voltage higher than 5V)
3. Breadboard and Jumper Wires
4. Voltage Source to Measure (e.g., battery, sensor, or adjustable power supply)
5. A computer with the Arduino IDE installed

---

Step 1: Understanding Voltage Measurement on Arduino

Arduino’s ADC converts analog voltages (0V to 5V on most boards) to a 10-bit digital value. This means the ADC provides a value between 0 and 1023, where 0 corresponds to 0V and 1023 corresponds to 5V (or the reference voltage).

Key Formula

To calculate the input voltage:

Voltage = (ADC_Value / 1023.0) * Reference_Voltage

Note: For most Arduino boards, the default reference voltage is 5V. If using the 3.3V variant, adjust the formula accordingly.

---

Step 2: Direct Voltage Measurement

For voltages up to 5V, you can connect the voltage source directly to an analog pin.

Wiring

Component	Arduino Pin
Voltage Source (+)	A0
Voltage Source (-)	GND

Example Code

#define analogPin A0

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

void loop() {
  int adcValue = analogRead(analogPin); // Read ADC value
  float voltage = (adcValue / 1023.0) * 5.0; // Convert to voltage

  Serial.print("Voltage: ");
  Serial.print(voltage, 2); // Print voltage with 2 decimal places
  Serial.println(" V");

  delay(1000); // Update every second
}

---

Step 3: Measuring Higher Voltages with a Voltage Divider

To measure voltages higher than 5V, use a voltage divider to scale down the input voltage.

Voltage Divider Formula

The voltage divider scales the input voltage using two resistors:

Vout = Vin * (R2 / (R1 + R2))

For example, to measure up to 12V:

• R1 = 10k ohms
• R2 = 10k ohms
• Scaling factor = 0.5 (Vout = Vin / 2)

Wiring

Component	Connection
Voltage Source (+)	Voltage Divider R1 Input
Voltage Divider R1/R2 Junction	Arduino A0
Voltage Source (-)	GND

Example Code

#define analogPin A0
const float R1 = 10000.0; // Resistor R1 value in ohms
const float R2 = 10000.0; // Resistor R2 value in ohms

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

void loop() {
  int adcValue = analogRead(analogPin); // Read ADC value
  float voltage = (adcValue / 1023.0) * 5.0; // Voltage at A0

  // Scale up to actual input voltage
  float inputVoltage = voltage * ((R1 + R2) / R2);

  Serial.print("Input Voltage: ");
  Serial.print(inputVoltage, 2); // Print with 2 decimal places
  Serial.println(" V");

  delay(1000); // Update every second
}

---

Step 4: Using an External Reference Voltage

For more accurate measurements, you can use an external reference voltage by connecting it to the AREF pin.

Steps to Set External Reference

1. Connect a stable reference voltage (e.g., 3.3V) to the AREF pin.
2. In the code, set the reference voltage:

analogReference(EXTERNAL);

3. Adjust calculations in the code for the new reference voltage.

---

Step 5: Best Practices for Accurate Measurements

1. Avoid Noise: Use short wires and proper grounding to reduce electrical noise.
2. Calibrate Your Setup: Verify readings with a multimeter to ensure accuracy.
3. Protect the Arduino: Use resistors or diodes to protect the analog input pin from overvoltage.
4. Filter Noisy Signals: Add a capacitor across the input to smooth out voltage fluctuations.

---

Applications of Voltage Measurement

1. Monitoring battery levels
2. Sensing analog signals from sensors
3. Measuring power supply voltages
4. DIY multimeter projects

---

Troubleshooting

1. Incorrect Readings:

   • Verify wiring and ensure correct resistor values for the voltage divider.
   • Check the reference voltage in calculations.

2. Fluctuating Values:

   • Add a capacitor (10µF or 100µF) across the input.

3. Overvoltage Protection:

   • Ensure input voltage does not exceed the voltage divider’s calculated limits.

---

Conclusion

Measuring voltage with an Arduino is straightforward and highly useful for many electronics projects. Whether you're monitoring battery levels or interfacing with sensors, understanding voltage measurement opens up a wide range of possibilities. Experiment with different setups and integrate voltage measurement into your projects!