AutocadHow-ToBeginner · 3 min read

How to Smooth Analog Readings in Arduino for Stable Sensor Data

To smooth analog readings in Arduino, use techniques like averaging multiple readings or applying a simple low-pass filter. These methods reduce noise by combining several samples or gradually adjusting the output to changes.

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Syntax

Here are two common ways to smooth analog readings:

Averaging multiple readings: Read the analog input several times, add the values, then divide by the number of readings.
Low-pass filter: Use a formula to slowly update the smoothed value based on the new reading and previous smoothed value.

arduino

// Averaging multiple readings
int readAnalogAverage(int pin, int samples) {
  long sum = 0;
  for (int i = 0; i < samples; i++) {
    sum += analogRead(pin);
  }
  return sum / samples;
}

// Simple low-pass filter
float smoothValue(float previous, float current, float alpha) {
  return alpha * current + (1 - alpha) * previous;
}

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Example

This example reads an analog sensor on pin A0 and smooths the readings using a low-pass filter. It prints the raw and smoothed values to the Serial Monitor.

arduino

const int sensorPin = A0;
float smoothedValue = 0;
const float alpha = 0.1; // smoothing factor (0-1)

void setup() {
  Serial.begin(9600);
  smoothedValue = analogRead(sensorPin); // initialize
}

void loop() {
  int rawValue = analogRead(sensorPin);
  smoothedValue = alpha * rawValue + (1 - alpha) * smoothedValue;
  Serial.print("Raw: ");
  Serial.print(rawValue);
  Serial.print(" Smoothed: ");
  Serial.println(smoothedValue);
  delay(100);
}

Output

Raw: 523 Smoothed: 523.00 Raw: 525 Smoothed: 523.20 Raw: 520 Smoothed: 522.48 Raw: 522 Smoothed: 522.23 Raw: 521 Smoothed: 522.10 ...

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Common Pitfalls

Common mistakes when smoothing analog readings include:

Using too few samples in averaging, which does not reduce noise well.
Choosing an alpha value in the low-pass filter that is too high (no smoothing) or too low (too slow response).
Not initializing the smoothed value before filtering, causing jumps on start.

arduino

// Wrong: no initialization of smoothedValue
float smoothedValue;

void loop() {
  int raw = analogRead(A0);
  smoothedValue = 0.1 * raw + 0.9 * smoothedValue; // smoothedValue undefined initially
}

// Right: initialize smoothedValue in setup
void setup() {
  smoothedValue = analogRead(A0);
}

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Quick Reference

Tips for smoothing analog readings:

Use 5-10 samples for averaging to balance noise reduction and speed.
Set low-pass filter alpha between 0.05 and 0.2 for smooth but responsive output.
Always initialize smoothed values before filtering.
Use delay() or timing to control reading frequency.

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Key Takeaways

Smooth analog readings by averaging multiple samples or using a low-pass filter.

Initialize your smoothed value before applying filtering to avoid startup errors.

Choose smoothing parameters carefully to balance noise reduction and responsiveness.

Averaging reduces random noise by combining readings; filtering smooths changes over time.

Test your smoothing method with your sensor to find the best settings.