diff --git a/Cargo.toml b/Cargo.toml
index 90a8c33..c250ece 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -14,7 +14,6 @@ embedded-hal = "0.2.3"
 nb = "0.1.2"
 ssd1306 = "0.3.0-alpha.4"
 switch-hal = "0.3.2"
-rotary-encoder-hal = "0.2.1"
 
 [dependencies.arrayvec]
 version = "0.5.1"
diff --git a/src/main.rs b/src/main.rs
index aa71156..c2db462 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,17 +1,22 @@
 #![no_std]
 #![no_main]
 
-use core::mem::MaybeUninit;
+use core::{
+    cell::RefCell,
+    fmt::Write,
+};
 
 use panic_halt as _;
 
 use cortex_m_rt::entry;
 
-use cortex_m::peripheral::NVIC;
+use cortex_m::{
+    interrupt::Mutex,
+};
 
 use stm32f1xx_hal::{
     afio,
-    device::EXTI,
+    device::{EXTI, NVIC},
     delay::Delay,
     i2c::{BlockingI2c, DutyCycle, Mode},
     gpio::{
@@ -48,11 +53,13 @@ use embedded_graphics::{
 };
 
 use arrayvec::ArrayString;
-use core::fmt::Write;
 
-static mut CLK_PIN: MaybeUninit<PA8<Input<Floating>>> = MaybeUninit::uninit();
-static mut DT_PIN: MaybeUninit<PA9<Input<Floating>>> = MaybeUninit::uninit();
-static mut COUNT: i32 = 0;
+type CLKPIN = PA8<Input<Floating>>;
+type DTPIN = PA9<Input<Floating>>;
+
+static CLK_PIN: Mutex<RefCell<Option<CLKPIN>>> = Mutex::new(RefCell::new(None));
+static DT_PIN: Mutex<RefCell<Option<DTPIN>>> = Mutex::new(RefCell::new(None));
+static COUNT: Mutex<RefCell<i32>> = Mutex::new(RefCell::new(0));
 
 #[entry]
 fn main() -> ! {
@@ -162,8 +169,8 @@ fn main() -> ! {
     // Microcontroller programs never exit main, so we must loop!
     loop {
         // Check our inputs
-        let counter = unsafe { &mut COUNT };
         let button = sw.is_active().unwrap();
+        let counter = cortex_m::interrupt::free(|cs| *COUNT.borrow(cs).borrow());
         if button_last && !button {
             led.toggle().unwrap();
         }
@@ -172,20 +179,21 @@ fn main() -> ! {
         let c = Circle::new(Point::new(cx, cy), C_RADIUS as u32)
             .into_styled(PrimitiveStyle::with_fill(BinaryColor::On));
 
+        // Show the position of the knob and thus the ball
         let mut textbuf = ArrayString::<[u8; 15]>::new();
-        write!(&mut textbuf, "count: {}", *counter).unwrap();
+        write!(&mut textbuf, "count: {}", counter).unwrap();
         let count = Text::new(&textbuf, Point::new(20, 36))
             .into_styled(TextStyle::new(Font6x8, BinaryColor::On));
+
         display.clear();
         c.draw(&mut display);
         t.draw(&mut display);
         count.draw(&mut display);
         display.flush().unwrap();
 
-        // Move down+right, come back from the other side if we go off-screen
-        cx = *counter;
-        //cx += 1;
-        //if cx > (DISPLAY_W + C_RADIUS) { cx = -C_RADIUS };
+        // Control the horizontal position with the knob
+        cx = counter.min(0).max(DISPLAY_W);
+        // Wrap the ball back to the top when it falls off the bottom
         cy += 1;
         if cy > (DISPLAY_H + C_RADIUS) { cy = -C_RADIUS };
 
@@ -193,30 +201,38 @@ fn main() -> ! {
 }
 
 fn init_encoder_pins(
-    clk: PA8<Input<Floating>>,
+    mut clk: PA8<Input<Floating>>,
     dt: PA9<Input<Floating>>,
     afio: &mut afio::Parts,
     exti: &EXTI,
 ) {
-    let clk_pin = unsafe { &mut *CLK_PIN.as_mut_ptr() };
-    let dt_pin = unsafe { &mut *DT_PIN.as_mut_ptr() };
+    cortex_m::interrupt::free(|cs| {
+        clk.make_interrupt_source(afio);
+        clk.trigger_on_edge(exti, Edge::RISING_FALLING);
+        clk.enable_interrupt(exti);
 
-    *clk_pin = clk;
-    *dt_pin = dt;
-
-    clk_pin.make_interrupt_source(afio);
-    clk_pin.trigger_on_edge(exti, Edge::RISING_FALLING);
-    clk_pin.enable_interrupt(exti);
+        CLK_PIN.borrow(cs).replace(Some(clk)).unwrap();
+        DT_PIN.borrow(cs).replace(Some(dt)).unwrap();
+    });
 }
 
 #[interrupt]
 fn EXTI9_5() {
+    static mut CLK: Option<CLKPIN> = None;
+    static mut DT: Option<DTPIN> = None;
     static mut PREV_A: bool = false;
     static mut PREV_C: bool = false;
 
-    let clk_pin = unsafe { &mut *CLK_PIN.as_mut_ptr() };
-    let dt_pin = unsafe { &mut *DT_PIN.as_mut_ptr() };
-    let counter = unsafe { &mut COUNT };
+    let clk_pin = CLK.get_or_insert_with(|| {
+        cortex_m::interrupt::free(|cs| {
+            CLK_PIN.borrow(cs).replace(None).unwrap()
+        })
+    });
+    let dt_pin = DT.get_or_insert_with(|| {
+        cortex_m::interrupt::free(|cs| {
+            DT_PIN.borrow(cs).replace(None).unwrap()
+        })
+    });
 
     if clk_pin.check_interrupt() {
         let a = clk_pin.is_high().unwrap();
@@ -228,9 +244,17 @@ fn EXTI9_5() {
             if b != *PREV_C {
                 *PREV_C = b;
                 if a == b { // Up
-                    *counter = counter.wrapping_add(1);
+                    cortex_m::interrupt::free(|cs| {
+                        COUNT
+                            .borrow(cs)
+                            .replace_with(|count| count.wrapping_add(1))
+                    });
                 } else {    // Down
-                    *counter = counter.wrapping_add(-1);
+                    cortex_m::interrupt::free(|cs| {
+                        COUNT
+                            .borrow(cs)
+                            .replace_with(|count| count.wrapping_add(-1))
+                    });
                 }
             }
         }