AutocadHow-ToBeginner · 4 min read

How to Measure Battery Voltage with Arduino Easily

To measure battery voltage with Arduino, use a voltage divider circuit to reduce the battery voltage to a safe level below 5V, then read it using analogRead(). Calculate the actual voltage by scaling the analog value according to the resistor ratio and Arduino's reference voltage.

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Syntax

Use the analogRead(pin) function to read voltage from an analog pin. The function returns a value from 0 to 1023 representing 0V to 5V (default Arduino reference voltage).

To measure battery voltage safely, connect the battery through a voltage divider made of two resistors to the analog pin.

analogRead(pin): Reads the analog voltage on the specified pin.
Voltage divider: Two resistors (R1 and R2) connected in series between battery positive and ground, with the junction connected to the analog pin.
Calculation: batteryVoltage = analogValue * (5.0 / 1023) * ((R1 + R2) / R2)

arduino

int analogPin = A0;  // Analog pin connected to voltage divider
int analogValue = analogRead(analogPin);  // Read analog value (0-1023)

// Resistor values in ohms
float R1 = 10000.0;  // Connected to battery positive
float R2 = 10000.0;  // Connected to ground

// Calculate battery voltage
float batteryVoltage = analogValue * (5.0 / 1023.0) * ((R1 + R2) / R2);

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Example

This example reads the battery voltage connected through a voltage divider to analog pin A0 and prints the voltage to the Serial Monitor every second.

arduino

const int analogPin = A0;
const float R1 = 10000.0;  // 10k ohm resistor
const float R2 = 10000.0;  // 10k ohm resistor

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

void loop() {
  int analogValue = analogRead(analogPin);
  float voltage = analogValue * (5.0 / 1023.0) * ((R1 + R2) / R2);
  Serial.print("Battery Voltage: ");
  Serial.print(voltage);
  Serial.println(" V");
  delay(1000);
}

Output

Battery Voltage: 3.30 V Battery Voltage: 3.29 V Battery Voltage: 3.30 V ...

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Common Pitfalls

Not using a voltage divider: Connecting battery voltage directly to Arduino analog pin can damage it if voltage > 5V.
Incorrect resistor values: Using wrong resistor values affects accuracy; use equal or known resistor values.
Ignoring Arduino reference voltage: Arduino default is 5V; if using 3.3V board, adjust calculations accordingly.
Not calibrating: Slight variations in resistors and Arduino voltage can cause errors; calibrate with a multimeter.

arduino

/* Wrong way: Direct connection without voltage divider
int analogValue = analogRead(A0);
float voltage = analogValue * (5.0 / 1023.0); // This can damage Arduino if voltage > 5V
*/

/* Right way: Use voltage divider and calculate actual voltage
int analogValue = analogRead(A0);
float voltage = analogValue * (5.0 / 1023.0) * ((R1 + R2) / R2);
*/

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Quick Reference

Use two resistors to create a voltage divider to keep voltage below 5V.
Read voltage with analogRead() on Arduino analog pin.
Calculate battery voltage with formula: voltage = analogValue * (5.0 / 1023) * ((R1 + R2) / R2).
Print or use the voltage value in your program.

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Key Takeaways

Always use a voltage divider to protect Arduino analog pins from high voltage.

Use analogRead() to get a value between 0 and 1023 representing 0 to 5 volts.

Calculate the real battery voltage by scaling the analog reading with resistor ratio.

Check resistor values and Arduino reference voltage for accurate measurements.

Calibrate your setup with a multimeter for best results.