How to Use Encoder KY-040: Examples, Pinouts, and Specs

The KY-040 is a rotary encoder that detects rotational position and direction. Unlike a potentiometer, which provides an absolute position, the KY-040 outputs quadrature pulses that indicate relative movement. This makes it ideal for applications requiring precise control or incremental adjustments. Additionally, the KY-040 includes a built-in push button, expanding its functionality for user interface controls.

• Volume control in audio systems
• Menu navigation in embedded systems
• Motor speed and position control
• Robotics and automation
• User interface controls for devices

The KY-040 rotary encoder has the following key specifications:

The KY-040 has 5 pins, as described in the table below:

1. Connect the Power Supply: Connect the + pin to a 3.3V or 5V power source and the GND pin to ground.
2. Connect the Rotary Encoder Outputs:
   • Connect the CLK and DT pins to digital input pins on your microcontroller.
   • These pins will output quadrature signals to indicate rotation direction and steps.
3. Connect the Push Button:
   • Connect the SW pin to a digital input pin on your microcontroller.
   • Use a pull-up resistor if your microcontroller does not have internal pull-ups.
4. Read the Signals:
   • Monitor the CLK and DT signals to detect rotation.
   • Monitor the SW signal to detect button presses.

• Debouncing: The mechanical nature of the encoder may cause signal noise. Use software debouncing or external capacitors to filter out unwanted noise.
• Pull-up Resistors: Ensure pull-up resistors are used for the SW, CLK, and DT pins if your microcontroller does not have internal pull-ups.
• Power Supply: Operate the KY-040 within its specified voltage range (3.3V to 5V) to avoid damage.

Below is an example of how to use the KY-040 with an Arduino UNO to detect rotation and button presses:

// Define pins for the KY-040 encoder
#define CLK 2  // Clock pin connected to digital pin 2
#define DT 3   // Data pin connected to digital pin 3
#define SW 4   // Switch pin connected to digital pin 4

int lastCLKState;  // To store the previous state of the CLK pin
int currentCLKState;  // To store the current state of the CLK pin
int counter = 0;  // Counter to track rotation steps

void setup() {
  pinMode(CLK, INPUT);  // Set CLK pin as input
  pinMode(DT, INPUT);   // Set DT pin as input
  pinMode(SW, INPUT_PULLUP);  // Set SW pin as input with pull-up resistor

  Serial.begin(9600);  // Initialize serial communication
  lastCLKState = digitalRead(CLK);  // Read the initial state of the CLK pin
}

void loop() {
  // Read the current state of the CLK pin
  currentCLKState = digitalRead(CLK);

  // Check if the CLK state has changed
  if (currentCLKState != lastCLKState) {
    // Determine rotation direction based on the DT pin state
    if (digitalRead(DT) != currentCLKState) {
      counter++;  // Clockwise rotation
    } else {
      counter--;  // Counterclockwise rotation
    }

    // Print the counter value to the serial monitor
    Serial.print("Counter: ");
    Serial.println(counter);
  }

  // Update the last CLK state
  lastCLKState = currentCLKState;

  // Check if the push button is pressed
  if (digitalRead(SW) == LOW) {
    Serial.println("Button Pressed!");
    delay(200);  // Debounce delay
  }
}

• The CLK and DT pins are used to detect rotation direction and steps.
• The SW pin is used to detect button presses.
• A debounce delay is added to avoid false triggers from the push button.

1. No Response from the Encoder:

   • Ensure the power supply is connected correctly to the + and GND pins.
   • Verify that the CLK and DT pins are connected to the correct digital input pins on the microcontroller.

2. Incorrect Rotation Direction:

   • Swap the connections of the CLK and DT pins to correct the direction.

3. Button Not Detected:

   • Check if the SW pin is connected properly.
   • Ensure a pull-up resistor is used if the microcontroller does not have internal pull-ups.

4. Noisy or Erratic Output:

   • Add software debouncing to filter out noise.
   • Use a small capacitor (e.g., 0.1µF) between the CLK and GND pins and between the DT and GND pins.

Q: Can the KY-040 be used with 3.3V microcontrollers like the ESP32?
A: Yes, the KY-040 operates at 3.3V to 5V, making it compatible with 3.3V microcontrollers.

Q: How many steps does the KY-040 encoder have per revolution?
A: The KY-040 has 20 steps per full revolution.

Q: Do I need external pull-up resistors for the KY-040?
A: If your microcontroller does not have internal pull-ups, you will need to add external pull-up resistors for the SW, CLK, and DT pins.

Q: Can I use the KY-040 for absolute position sensing?
A: No, the KY-040 is a relative encoder and does not provide absolute position information.