KY-040 on OLED: Rotary Encoder Counter
Overview & Wiring
What it is: The KY-040 is a rotary encoder — a knob you can turn endlessly in either direction, plus a built-in push button. It's the input device for menus, volume controls and setting values.
How it works: Turning the knob produces two square waves (CLK and DT) 90° out of phase. By checking DT at the moment CLK changes, you know the direction. The shaft also presses down as a button (SW). All digital.
Wiring:
KY-040 CLK -> GPIO10
KY-040 DT -> GPIO6
KY-040 SW -> GPIO7 (push button)
KY-040 + -> 3V3
KY-040 GND -> GND
OLED VCC=3V3, GND=GND, SDA=GPIO4, SCL=GPIO5
Libraries: only "Adafruit SSD1306" and "Adafruit GFX Library".
On screen / Serial: a counter that goes up when you turn one way and down the other. Press the knob to reset to 0.
Gotchas: Cheap encoders bounce; this sketch reads on the CLK falling edge to reduce it, but for heavy use add small capacitors or use an interrupt-based library. The internal button needs a pull-up (enabled in code).
Circuit Diagram
Parts You Need
Source Code (Arduino / ESP32)
#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>
Adafruit_SSD1306 display(128, 64, &Wire, -1);
#define CLK 10
#define DT 6
#define SW 7
long counter = 0;
int lastClk;
void setup() {
Serial.begin(115200);
Wire.begin(4, 5);
display.begin(SSD1306_SWITCHCAPVCC, 0x3C);
pinMode(CLK, INPUT);
pinMode(DT, INPUT);
pinMode(SW, INPUT_PULLUP); // button active-LOW
lastClk = digitalRead(CLK);
}
void loop() {
int clk = digitalRead(CLK);
if (clk != lastClk && clk == LOW) { // falling edge of CLK
if (digitalRead(DT) != clk) counter++; // DT leads -> clockwise
else counter--;
Serial.printf("Count: %ld\n", counter);
}
lastClk = clk;
if (digitalRead(SW) == LOW) { counter = 0; } // press resets
display.clearDisplay();
display.setTextColor(SSD1306_WHITE);
display.setTextSize(1);
display.setCursor(0, 0);
display.println("KY-040 Encoder");
display.setTextSize(3);
display.setCursor(0, 26);
display.printf("%ld", counter);
display.display();
}