diff --git a/Makefile b/Makefile
index 2846746..54594ce 100644
--- a/Makefile
+++ b/Makefile
@@ -8,7 +8,7 @@ COMFLAGS=-g -Os -pedantic -Wall
 CFLAGS=$(COMFLAGS) -std=c99 -D_POSIX_C_SOURCE=200809L
 CXXFLAGS=$(COMFLAGS) -std=c++17
 
-OBJS = usb.o adc.o ringbuffer.o uart.o buttons.o printf.o
+OBJS = usb.o adc.o ringbuffer.o uart.o buttons.o printf.o encoder.o
 BINARY ?= main
 DEVICE=STM32F405RG
 
diff --git a/encoder.c b/encoder.c
new file mode 100644
index 0000000..f0e0f61
--- /dev/null
+++ b/encoder.c
@@ -0,0 +1,74 @@
+#include <libopencm3/cm3/nvic.h>
+#include <libopencm3/stm32/exti.h>
+#include <libopencm3/stm32/gpio.h>
+#include <libopencm3/stm32/rcc.h>
+#include <stdint.h>
+#include <stddef.h>
+#include "encoder.h"
+
+static volatile int pos;
+
+static void check(void);
+
+#define PIN1 GPIO4
+#define PIN1_IRQ NVIC_EXTI4_IRQ
+#define PIN2 GPIO5
+#define PIN2_IRQ NVIC_EXTI9_5_IRQ
+
+void encoder_setup(void) {
+        rcc_periph_clock_enable(RCC_GPIOA);
+
+        gpio_mode_setup(GPIOA, GPIO_MODE_INPUT, GPIO_PUPD_NONE, PIN1 | PIN2);
+
+        /* Set up exti on A0 & A1 */
+        exti_select_source(PIN1 | PIN2, GPIOA);
+        exti_set_trigger(PIN1 | PIN2, EXTI_TRIGGER_BOTH);
+        exti_enable_request(PIN1 | PIN2);
+
+        nvic_enable_irq(PIN1_IRQ);
+        nvic_enable_irq(PIN2_IRQ);
+}
+
+int encoder_get() {
+        return pos;
+}
+
+static int prev = 0;
+void check(void) {
+        int pp = pos;
+        int now = GPIO_IDR(GPIOA);
+        now = (!!(now & PIN1))<<0 | (!!(now & PIN2)) << 1;
+
+        switch (prev << 2 | now) {
+        case 0 * 4 + 2:
+        case 1 * 4 + 0:
+        case 2 * 4 + 3:
+        case 3 * 4 + 1:
+                pos++;
+                break;
+        case 0 * 4 + 1:
+        case 1 * 4 + 3:
+        case 2 * 4 + 0:
+        case 3 * 4 + 2:
+                pos--;
+                break;
+        default:
+                prev = now;
+                return;
+        }
+
+        prev = now;
+        if (pos < MIN_POS)
+                pos = MIN_POS;
+        if (pos > MAX_POS)
+                pos = MAX_POS;
+}
+
+void exti4_isr(void) {
+        exti_reset_request(EXTI4);
+        check();
+}
+void exti9_5_isr(void) {
+        exti_reset_request(EXTI5);
+        check();
+}
diff --git a/encoder.h b/encoder.h
new file mode 100644
index 0000000..d5fd2c5
--- /dev/null
+++ b/encoder.h
@@ -0,0 +1,11 @@
+#ifndef ENCODER_H
+#define ENCODER_H
+#define CLOSED_POS 220
+#define OPENED_POS 0
+
+#define MAX_POS ((CLOSED_POS > OPENED_POS) ? CLOSED_POS : OPENED_POS)
+#define MIN_POS ((CLOSED_POS < OPENED_POS) ? CLOSED_POS : OPENED_POS)
+
+void encoder_setup(void);
+int encoder_get(void);
+#endif