diff --git a/ports/stm32f4/common-hal/pulseio/PulseIn.c b/ports/stm32f4/common-hal/pulseio/PulseIn.c
index 068936bdd0..d361a1e9a7 100644
--- a/ports/stm32f4/common-hal/pulseio/PulseIn.c
+++ b/ports/stm32f4/common-hal/pulseio/PulseIn.c
@@ -34,46 +34,295 @@
 #include "shared-bindings/pulseio/PulseIn.h"
 #include "tick.h"
 
+#include "stm32f4xx_hal.h"
+
+#define STM32_GPIO_PORT_SIZE 16
+
+static pulseio_pulsein_obj_t* _objs[STM32_GPIO_PORT_SIZE];
+
+static void assign_EXTI_Interrupt(pulseio_pulsein_obj_t* self, uint8_t num);
+
+static void pulsein_handler(uint8_t num) {
+    // Grab the current time first.
+    uint32_t current_us;
+    uint64_t current_ms;
+    current_tick(&current_ms, &current_us);
+
+    // current_tick gives us the remaining us until the next tick but we want the number since the last ms.
+    current_us = 1000 - current_us;
+
+    pulseio_pulsein_obj_t* self = _objs[num];
+    if ( !self ) return;
+
+    if (self->first_edge) {
+        // first pulse is opposite state from idle
+        bool state = HAL_GPIO_ReadPin(pin_port(self->pin->port), pin_mask(self->pin->number));
+        if ( self->idle_state != state ) {
+            self->first_edge = false;
+        }
+    } else {
+        uint32_t ms_diff = current_ms - self->last_ms;
+        uint16_t us_diff = current_us - self->last_us;
+        uint32_t total_diff = us_diff;
+
+        if (self->last_us > current_us) {
+            total_diff = 1000 + current_us - self->last_us;
+            if (ms_diff > 1) {
+                total_diff += (ms_diff - 1) * 1000;
+            }
+        } else {
+            total_diff += ms_diff * 1000;
+        }
+        uint16_t duration = 0xffff;
+        if (total_diff < duration) {
+            duration = total_diff;
+        }
+
+        uint16_t i = (self->start + self->len) % self->maxlen;
+        self->buffer[i] = duration;
+        if (self->len < self->maxlen) {
+            self->len++;
+        } else {
+            self->start++;
+        }
+    }
+
+    self->last_ms = current_ms;
+    self->last_us = current_us;
+}
+
 void pulsein_reset(void) {
+    // Disable all active interrupts and clear array
+    for (uint i = 0; i < STM32_GPIO_PORT_SIZE; i++) {
+        if (_objs[i] != NULL) {
+            HAL_NVIC_DisableIRQ(_objs[i]->irq);
+        }
+    }
+    memset(_objs, 0, sizeof(_objs));
 }
 
 void common_hal_pulseio_pulsein_construct(pulseio_pulsein_obj_t* self, const mcu_pin_obj_t* pin,
                                              uint16_t maxlen, bool idle_state) {
-    mp_raise_NotImplementedError(translate("PulseIn not yet supported"));
+    // STM32 has one shared EXTI for each pin number, 0-15
+    uint8_t p_num = pin->number;
+    if(_objs[p_num]) {
+        mp_raise_ValueError(translate("Pin number already reserved by EXTI"));
+    }
+    _objs[p_num] = self;
+
+    // Allocate pulse buffer
+    self->buffer = (uint16_t *) m_malloc(maxlen * sizeof(uint16_t), false);
+    if (self->buffer == NULL) {
+        mp_raise_msg_varg(&mp_type_MemoryError, translate("Failed to allocate RX buffer of %d bytes"), 
+                          maxlen * sizeof(uint16_t));
+    }
+    
+    // Set internal variables
+    self->pin = pin;
+    self->maxlen = maxlen;
+    self->idle_state = idle_state;
+    self->start = 0;
+    self->len = 0;
+    self->first_edge = true;
+    self->paused = false;
+    self->last_us = 0;
+    self->last_ms = 0;
+
+    // EXTI pins can also be read as an input
+    GPIO_InitTypeDef GPIO_InitStruct = {0};
+    GPIO_InitStruct.Pin = pin_mask(pin->number);
+    GPIO_InitStruct.Mode = GPIO_MODE_IT_RISING_FALLING;
+    GPIO_InitStruct.Pull = GPIO_NOPULL;
+    HAL_GPIO_Init(pin_port(pin->port), &GPIO_InitStruct);
+
+    // Interrupt starts immediately
+    assign_EXTI_Interrupt(self, pin->number);
+    HAL_NVIC_EnableIRQ(self->irq);
+    claim_pin(pin);
 }
 
 bool common_hal_pulseio_pulsein_deinited(pulseio_pulsein_obj_t* self) {
-  return true;
+    return (self->pin == NULL);
 }
 
 void common_hal_pulseio_pulsein_deinit(pulseio_pulsein_obj_t* self) {
+    if (common_hal_pulseio_pulsein_deinited(self)) {
+        return;
+    }
+    HAL_NVIC_DisableIRQ(self->irq);
+    _objs[self->pin->number] = NULL;
+    reset_pin_number(self->pin->port, self->pin->number);
+    self->pin = NULL;
 }
 
 void common_hal_pulseio_pulsein_pause(pulseio_pulsein_obj_t* self) {
+    HAL_NVIC_DisableIRQ(self->irq);
+    self->paused = true;
 }
 
 void common_hal_pulseio_pulsein_resume(pulseio_pulsein_obj_t* self, uint16_t trigger_duration) {
+    // Make sure we're paused.
+    if ( !self->paused ) {
+        common_hal_pulseio_pulsein_pause(self);
+    }
+
+    // Send the trigger pulse.
+    if (trigger_duration > 0) {
+        GPIO_InitTypeDef GPIO_InitStruct = {0};
+        GPIO_InitStruct.Pin = pin_mask(self->pin->number);
+        GPIO_InitStruct.Mode = GPIO_MODE_OUTPUT_PP;
+        GPIO_InitStruct.Pull = GPIO_NOPULL;
+        GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;
+        HAL_GPIO_Init(pin_port(self->pin->port), &GPIO_InitStruct);
+
+        HAL_GPIO_WritePin(pin_port(self->pin->port), pin_mask(self->pin->number), !self->idle_state);
+        common_hal_mcu_delay_us((uint32_t)trigger_duration);
+        HAL_GPIO_WritePin(pin_port(self->pin->port), pin_mask(self->pin->number), self->idle_state);
+
+        GPIO_InitStruct.Pin = pin_mask(self->pin->number);
+        GPIO_InitStruct.Mode = GPIO_MODE_IT_RISING_FALLING;
+        GPIO_InitStruct.Pull = GPIO_NOPULL;
+        HAL_GPIO_Init(pin_port(self->pin->port), &GPIO_InitStruct);
+    }
+
+    self->first_edge = true;
+    self->paused = false;
+    self->last_ms = 0;
+    self->last_us = 0;
+
+    HAL_NVIC_EnableIRQ(self->irq);
 }
 
 void common_hal_pulseio_pulsein_clear(pulseio_pulsein_obj_t* self) {
+    HAL_NVIC_DisableIRQ(self->irq);
+    self->start = 0;
+    self->len = 0;
+    HAL_NVIC_EnableIRQ(self->irq);
 }
 
 uint16_t common_hal_pulseio_pulsein_get_item(pulseio_pulsein_obj_t* self, int16_t index) {
-    return 0;
+    HAL_NVIC_DisableIRQ(self->irq);
+    if (index < 0) {
+        index += self->len;
+    }
+    if (index < 0 || index >= self->len) {
+        HAL_NVIC_EnableIRQ(self->irq);
+        mp_raise_IndexError(translate("index out of range"));
+    }
+    uint16_t value = self->buffer[(self->start + index) % self->maxlen];
+    HAL_NVIC_EnableIRQ(self->irq);
+    return value;
 }
 
 uint16_t common_hal_pulseio_pulsein_popleft(pulseio_pulsein_obj_t* self) {
-    return 0;
+    if (self->len == 0) {
+        mp_raise_IndexError(translate("pop from an empty PulseIn"));
+    }
+    HAL_NVIC_DisableIRQ(self->irq);
+    uint16_t value = self->buffer[self->start];
+    self->start = (self->start + 1) % self->maxlen;
+    self->len--;
+    HAL_NVIC_EnableIRQ(self->irq);
+
+    return value;
 }
 
 uint16_t common_hal_pulseio_pulsein_get_maxlen(pulseio_pulsein_obj_t* self) {
-    return 0;
+    return self->maxlen;
 }
 
 bool common_hal_pulseio_pulsein_get_paused(pulseio_pulsein_obj_t* self) {
-    return 0;
+    return self->paused;
 }
 
 uint16_t common_hal_pulseio_pulsein_get_len(pulseio_pulsein_obj_t* self) {
-    return 0;
+    return self->len;
+}
+
+static void assign_EXTI_Interrupt(pulseio_pulsein_obj_t* self, uint8_t num) {
+    if (num == 0) {
+        self->irq = EXTI0_IRQn;
+    } else if (num == 1) {
+        self->irq = EXTI1_IRQn;
+    } else if (num == 2) {
+        self->irq = EXTI2_IRQn;
+    } else if (num == 3) {
+        self->irq = EXTI3_IRQn;
+    } else if (num == 4) {
+        self->irq = EXTI4_IRQn;
+    } else if (num >= 5 && num <= 9 ) {
+        self->irq = EXTI9_5_IRQn;
+    } else if (num >= 10 && num <= 15) {
+        self->irq = EXTI15_10_IRQn;
+    }
+}
+
+void EXTI0_IRQHandler(void)
+{
+    EXTI->PR = 1 << 0;
+    pulsein_handler(0);
+}
+void EXTI1_IRQHandler(void)
+{
+    EXTI->PR = 1 << 1;
+    pulsein_handler(1);
+}
+void EXTI2_IRQHandler(void)
+{
+    EXTI->PR = 1 << 2;
+    pulsein_handler(2);
+}
+void EXTI3_IRQHandler(void)
+{
+    EXTI->PR = 1 << 3;
+    pulsein_handler(3);
+}
+void EXTI4_IRQHandler(void)
+{
+    EXTI->PR = 1 << 4;
+    pulsein_handler(4);
+}
+void EXTI9_5_IRQHandler(void)
+{
+    uint32_t pending = EXTI->PR;
+    if(pending & (1 << 5)) {
+        EXTI->PR = 1 << 5;
+        pulsein_handler(5);
+    } else if (pending & (1 << 6)) {
+        EXTI->PR = 1 << 6;
+        pulsein_handler(6);
+    } else if (pending & (1 << 7)) {
+        EXTI->PR = 1 << 7;
+        pulsein_handler(7);
+    } else if (pending & (1 << 8)) {
+        EXTI->PR = 1 << 8;
+        pulsein_handler(8);
+    } else if (pending & (1 << 9)) {
+        EXTI->PR = 1 << 9;
+        pulsein_handler(9);
+    }
+}
+
+void EXTI15_10_IRQHandler(void)
+{
+    uint32_t pending = EXTI->PR;
+    if(pending & (1 << 10)) {
+        EXTI->PR = 1 << 10;
+        pulsein_handler(10);
+    } else if (pending & (1 << 11)) {
+        EXTI->PR = 1 << 11;
+        pulsein_handler(11);
+    } else if (pending & (1 << 12)) {
+        EXTI->PR = 1 << 12;
+        pulsein_handler(12);
+    } else if (pending & (1 << 13)) {
+        EXTI->PR = 1 << 13;
+        pulsein_handler(13);
+    } else if (pending & (1 << 14)) {
+        EXTI->PR = 1 << 14;
+        pulsein_handler(14);
+    } else if (pending & (1 << 15)) {
+        EXTI->PR = 1 << 15;
+        pulsein_handler(15);
+    }
 }
diff --git a/ports/stm32f4/common-hal/pulseio/PulseIn.h b/ports/stm32f4/common-hal/pulseio/PulseIn.h
index 2538b07ab5..5456613c6a 100644
--- a/ports/stm32f4/common-hal/pulseio/PulseIn.h
+++ b/ports/stm32f4/common-hal/pulseio/PulseIn.h
@@ -34,7 +34,8 @@
 typedef struct {
     mp_obj_base_t base;
 
-    uint8_t pin;
+    const mcu_pin_obj_t* pin;
+    IRQn_Type irq;
     bool idle_state;
     bool paused;
     volatile bool first_edge;
diff --git a/ports/stm32f4/supervisor/port.c b/ports/stm32f4/supervisor/port.c
index ecb4d3d15c..948e9f2e4a 100644
--- a/ports/stm32f4/supervisor/port.c
+++ b/ports/stm32f4/supervisor/port.c
@@ -36,6 +36,7 @@
 #include "common-hal/busio/UART.h"
 #include "common-hal/pulseio/PWMOut.h"
 #include "common-hal/pulseio/PulseOut.h"
+#include "common-hal/pulseio/PulseIn.h"
 
 #include "stm32f4/clocks.h"
 #include "stm32f4/gpio.h"
@@ -62,6 +63,7 @@ void reset_port(void) {
     uart_reset();
     pwmout_reset();
     pulseout_reset();
+    pulsein_reset();
 }
 
 void reset_to_bootloader(void) {