Input devices

EC11 rotary encoder with ESP32

A rotary encoder gives a display board a real knob: turn to change a value, press to confirm. The EC11 is a common mechanical type with two signal pins, A and B, plus a push switch. It has no absolute position. You only count steps and direction from which signal changes first.

There is no power pin on a bare EC11. Connect the common pin to GND, A and B to two GPIOs, and enable the internal pull-ups. Modules with a small PCB add resistors and may have a VCC pin, which should go to 3.3 V, not 5 V, on an ESP32. Alps lists contact bounce of up to 2 ms, so read it with interrupts and tolerate a few false edges.

Models differ, which explains most 'it counts by two' complaints. Sources list 15, 18, 20 and 30 detents, and 9 or 15 pulses per turn, so one click may produce one or more steps. Adjust the divider in your code. Some boards, such as the MaTouch Rotary, already have a knob, and LCD Ultra Pro supports those.

EC11 rotary encoder wiring diagram for ESP32 — Wiring diagram drawn by LCD Ultra Pro.

Specifications

Type	Incremental, A/B quadrature
Detents	15, 18, 20 or 30, by model
Pulses per turn	9 to 20, by model
Voltage	Up to 5 V, use 3.3 V on an ESP32
Contact bounce	Up to 2 ms (Alps)
Extra	Push switch on most models

Power and logic levels

3.3 V: safe to connect directly

Supply	None, it is a switch
Signal level	Follows the pull-up
On an ESP32	Use pull-ups to 3V3.

ESP32 pins, including those on a display board's connectors, work at 3.3 V and are not 5 V tolerant. Modules differ, so if in doubt, measure the signal before you connect it.

Wiring

EC11 rotary encoder	Connect to	Note
A	GPIO 5	Internal pull-up
B	GPIO 6	Internal pull-up
C (common)	GND
SW	GPIO 7	Internal pull-up
SW GND	GND

Arduino code

const int A_PIN = 5, B_PIN = 6, SW_PIN = 7;
volatile long steps = 0;

void IRAM_ATTR onA() {
  steps += digitalRead(B_PIN) == digitalRead(A_PIN) ? -1 : 1;
}

void setup() {
  Serial.begin(115200);
  pinMode(A_PIN, INPUT_PULLUP);
  pinMode(B_PIN, INPUT_PULLUP);
  pinMode(SW_PIN, INPUT_PULLUP);
  attachInterrupt(digitalPinToInterrupt(A_PIN), onA, CHANGE);
}

void loop() {
  static long last = 0;
  long now = steps;
  if (now != last) {
    Serial.println(now);
    last = now;
  }
  if (digitalRead(SW_PIN) == LOW) Serial.println("Pressed");
  delay(20);
}

No extra library needed. Compiled for ESP32-S3 with arduino-esp32 3.x. Not yet tested by us on a physical sensor. Change the pins to match your board.

On a display

Read the value in your sketch and pass it to a label, or send it over MQTT and show it with an MQTT value in the editor.

Design a display for EC11 rotary encoder

Boards with a ready connector

Only boards whose connectors we have surveyed. Others may still work on free GPIOs.

LilyGO T-Display (classic) 1.14"	Left pin header: GPIO 21, 22, 17
M5Stack AtomS3 0.85"	Bottom pin header: GPIO 5, 6, 7
M5Stack M5StickC Plus2 1.14"	Top HAT header: GPIO 26, 25, 36GPIO 25 and GPIO 36 are on the same header pin — use only one of them (36 is input-only)
Waveshare ESP32-S3 Touch LCD 1.28" round	SH1.0 GPIO header: GPIO 15, 16, 17Six GPIOs led out per the wiki pin table
Waveshare ESP32-S3 Touch LCD 1.28" round (CNC metal housing)	SH1.0 GPIO header: GPIO 15, 16, 17Six GPIOs led out per the wiki pin table

Good to know

Use 3.3 V on module VCC pins with an ESP32.
One click can give more than one step. Adjust by model.
Expect some bounce. Filter it in software.
LVGL needs focus groups to navigate with a knob.

What it is good for

Menu navigation
Volume and brightness
Thermostat setpoints

FAQ

Why does my encoder count two steps per click?

Models differ. Divide the count to match your detents.

Does the EC11 need power?

A bare EC11 does not. Use the internal pull-ups and connect common to GND.

Why does one click count as two steps?

Encoder models differ in detents and pulses per turn. Divide the count to match yours.

Sources

https://www.avnet.com/opasdata/d120001/medias/docus/196/Alps-Alpine-EC11-Series-EN-Datasheet.pdf

Related parts

Use this information at your own risk. It is for general guidance only: the example code compiles, but it has not been tested on every part, and modules differ between sellers. Check the manufacturer's data before you build. Product names belong to their owners, and LCD Ultra Pro is not affiliated with them. See our Terms.