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#30 · Sound sensor data on Arduino IDE serial plotter

Tutorial goals

  • ✓ Reading CZN-15E sound sensor
  • ✓ Applying data sampling
  • ✓ Draw sound on serial plotter

Components needed

  • 1× Arduino
  • 3× Jumper wire (male-female)
  • 1× CZN-15E sound sensor


In this tutorial Bas is showing how to use a sound sensor to show audio on the serial plotter. He explains that the sensor captures sound waves with a microphone and translates them into resistance which is the same as the amount of sound. When there is low resistance, the sensor sends 5V to the OUT and when there is lot of sound it sends around 0V. The potentiometer on the sensor can be adjusted to set the level of the boundary that determines whether the signal will be seen as LOW or HIGH. Then, Bas demonstrates how to build the circuit, connect the sensor to the Arduino, and run the code. To display the intensity of the sound, he shows how to use the serial plotter. He also mentions that he changed the code to sample the audio and use millis() to measure the elapsed milliseconds since the last time.


In this tutorial you will learn how to read the CZN-15E sound sensor and display it on the serial plotter of the Arduino IDE. You will also learn what data sampling is, and how you can use it to approximate sound volume. 🤓

Course material

At the bottom of this page you'll find the course material button. This button allows you to download the code, circuit diagram and other files relevant to this Arduino tutorial.

CZN-15E sound sensor

CZN-15E sound sensor
CZN-15E sound sensor

The CZN-15E sound sensor can measure whether sound is present. This makes it possible, for example, to make a clap sensor. Unlike a microphone, it does not measure the frequency or volume of the sound. It is a binary sensor that only indicates whether sound is detected.

sound sensor operation
sound sensor operation

In the upper part of the figure you can see sound waves reaching the sensor. The microphone converts this to a resistance. This resistance changes as the sound is louder or softer. The sensor then determines whether the resistance is above a certain threshold. Once this is the case the OUT pin on the sensor will change from LOW to HIGH.

sensitivity control
sensitivity control

The sensitivity of the sensor is adjustable. On top of the sensor is a blue square block. With a small screwdriver you can turn the center to the left or right. This sets the correct sensitivity.

The circuit

Connect the sensor according to the diagram below.

The CZN-15E sound sensor connected to the Arduino
The CZN-15E sound sensor connected to the Arduino

We use the following jumper wires

  • The 5V on the Arduino -> VCC pin of the sensor
  • The GND on the Arduino -> GND pin of the sensor
  • Pin 8 on the Arduino -> OUT pin of the sensor

Arduino Code - part 1

The code below reads the OUT_PIN (pin 8) and then sends the measured value to the serial monitor.

1 const int OUT_PIN = 8;
3 void setup() {
4   Serial.begin(9600);
5 }
7 void loop() {
8   Serial.println(digitalRead(OUT_PIN));
9 }

Upload this code to your Arduino and open the serial monitor in the Arduino IDE:

Tools ▸ Serial Monitor

You should see 1 and 0 passing by when you make a sound. Here 0 is for silence and 1 for when there is sound.

serial monitor
serial monitor

Serial plotter

In addition to the serial monitor, the Arduino has another handy tool: the serial plotter. With this tool you can display data in real time over time. This can be used for example for temperature graphs.

You can access the serial plotter from the menu at the top of the IDE:

Tools ▸ Serial Plotter

The ones and zeros of the serial monitor should now be displayed in a graph.

serial plotter
serial plotter

Data sampling

For part 2 of this tutorial we will use data sampling. This means that we will measure a certain value at a fixed interval (sample time), for example 10ms. For example, you can count how often a certain value has occurred within the sample time. Then display the result of this count in a graph.

Arduino Code - part 2

We start by defining two constants and four variables:

1 const int OUT_PIN = 8;
2 const int SAMPLE_TIME = 10;
3 unsigned long millisCurrent;
4 unsigned long millisLast = 0;
5 unsigned long millisElapsed = 0;
6 int sampleBufferValue = 0;
  • OUT_PIN is the pin to which we connected the sensor.
  • SAMPLE_TIME is the number of milliseconds in which we measure the data for one sample.
  • We use millisCurrent, millisLast and millisElapsed to keep track of how much time has passed.
  • We use sampleBufferValue to store how many times there has been sound within the sample time.


1 void setup()
2 { 
3   Serial.begin(9600);
4 }

In the setup() we do nothing but set the serial monitor to 9600 Baud.


1 void loop() {
3   millisCurrent = millis();
4   millisElapsed = millisCurrent - millisLast;
6   if (digitalRead(OUT_PIN) == LOW) {
7     sampleBufferValue++;
8   }
10   if (millisElapsed > SAMPLE_TIME) {
11     Serial.println(sampleBufferValue);
12     sampleBufferValue = 0;
13     millisLast = millisCurrent;
14   }
16 }

The loop() function consists of 3 parts:

  • Calculate elapsed time
  • Read sensor
  • Check if the sample time has elapsed


When calculating the elapsed time, we use the mills() function. This returns the number of milliseconds elapsed since the Arduino was booted. The returned number is of type unsigned long. After about 50 days the highest number is reached, the Arduino will then start counting again from 0.

1 millisCurrent = millis();
2 millisElapsed = millisCurrent - millisLast;

First we store the number of elapsed milliseconds in the variable millisCurrent. Then we can calculate how much time has passed since the last time by subtracting millisLast. We store this in the variable millisElapsed. The first time millisLast is still at 0, so millisElapsed is equal to millisCurrent.

Reading the sensor

We use digitalRead() to read the sensor.

1 if (digitalRead(OUT_PIN) == LOW) {
2   sampleBufferValue++;
3 }

If the value read is equal to LOW we increment sampleBufferValue by 1. The abbreviated notation for this is sampleBufferValue++.

🎓 Can you indicate why we are checking here if the sensor is LOW?

Monitor Elapsed Sample Time

We don't yet have a way to determine if the sample time has expired. We'll do that in the last part of the code.

1 if (millisElapsed > SAMPLE_TIME) {
2   Serial.println(sampleBufferValue);
3   sampleBufferValue = 0;
4   millisLast = millisCurrent;
5 }

The moment the elapsed time (millisElapsed) is greater than the time that a sample is allowed to last, we will do a number of things. First we print the value of the buffer (sampleBufferValue) to the serial monitor. sampleBufferValue contains how many times the sensor in the current sample has sensed sound.

After this we start a new sample measurement. We set the sampleBufferValue (ie how often sound was detected) back to 0. Finally, we make millisLast equal to millisCurrent so that we can recalculate the elapsed time of the current sample.

Upload code to Arduino

You can now upload the code to the Arduino.

serial plotter with sampled data
serial plotter with sampled data

Open the serial plotter to display the sampled values from the sensor.

Tools ▸ Serial plotter

The X and Y axis

The x-axis (horizontal) is the time axis. We set SAMPLE_TIME to 10ms. This means that each horizontal point is equal to 10ms. So if we see the number 100 on the x-axis (100x 10ms), 1 second has passed.

The y-axis (vertical) is the number of moments within 10ms that the Arduino sensed sound. This is related to how fast the Arduino can go through the loop(). For example, an 8Mhz Arduino will be able to do fewer measurements per second than a 16Mhz Arduino. They are therefore not exact values, but should be viewed more relative to each other.

#30 · Sound sensor data on Arduino IDE serial plotter schakelschema