diff --git a/Core/Inc/FanControl.h b/Core/Inc/FanControl.h
index 6d0eef0..a9fdfca 100644
--- a/Core/Inc/FanControl.h
+++ b/Core/Inc/FanControl.h
@@ -5,8 +5,14 @@
 #include "stm32f4xx_hal_def.h"
 #include "stm32f4xx_hal_tim.h"
 
+typedef enum { FANS_OFF, FANS_ON } FanState;
+
+extern FanState fan_state;
+
 HAL_StatusTypeDef fan_ctrl_init(TIM_HandleTypeDef* handle, uint32_t channel);
 
+void fan_ctrl_update();
+
 /**
  * @brief Set the power of the fan (0 -> off, 100 -> full power).
  */
diff --git a/Core/Inc/main.h b/Core/Inc/main.h
index 88b5bfb..44e1912 100644
--- a/Core/Inc/main.h
+++ b/Core/Inc/main.h
@@ -59,6 +59,10 @@ extern uint8_t slave_id;
 #define THRESH_OV 55050        /* 4.2V */
 #define THRESH_UT 0            /* 0C */
 #define THRESH_OT 880          /* 55C */
+
+#define THRESH_FANS_ON_HALF 640 /* 40C */
+#define THRESH_FANS_ON_FULL 800 /* 50C */
+#define THRESH_FANS_OFF 560     /* 35C */
 /* USER CODE END EM */
 
 void HAL_TIM_MspPostInit(TIM_HandleTypeDef* htim);
diff --git a/Core/Src/FanControl.c b/Core/Src/FanControl.c
index 7258526..f7c74be 100644
--- a/Core/Src/FanControl.c
+++ b/Core/Src/FanControl.c
@@ -1,18 +1,48 @@
 #include "FanControl.h"
 
+#include "TMP144.h"
+#include "main.h"
+
 #include "stm32f4xx_hal_def.h"
 #include "stm32f4xx_hal_tim.h"
 
+#include <stdint.h>
+
 TIM_HandleTypeDef* timer;
 uint32_t channel;
+FanState fan_state;
 
 HAL_StatusTypeDef fan_ctrl_init(TIM_HandleTypeDef* handle, uint32_t channel_) {
   timer = handle;
   channel = channel_;
+  fan_state = FANS_OFF;
 
   return HAL_TIM_PWM_Start(timer, channel);
 }
 
+void fan_ctrl_update() {
+  if (fan_state == FANS_OFF && max_temperature > THRESH_FANS_ON_HALF) {
+    fan_state = FANS_ON;
+  } else if (fan_state == FANS_ON && max_temperature < THRESH_FANS_OFF) {
+    fan_state = FANS_OFF;
+  }
+
+  uint32_t power;
+  if (fan_state == FANS_OFF) {
+    power = 0;
+  } else {
+    if (max_temperature < THRESH_FANS_ON_HALF) {
+      power = 50;
+    } else if (max_temperature > THRESH_FANS_ON_FULL) {
+      power = 100;
+    } else {
+      power = (100 * (max_temperature - THRESH_FANS_ON_HALF)) /
+              (THRESH_FANS_ON_FULL - THRESH_FANS_ON_HALF);
+    }
+  }
+  fan_ctrl_set_power(power);
+}
+
 void fan_ctrl_set_power(uint32_t percent) {
   if (percent > 100) {
     percent = 100;
diff --git a/Core/Src/main.c b/Core/Src/main.c
index a572064..5a7aabd 100644
--- a/Core/Src/main.c
+++ b/Core/Src/main.c
@@ -188,6 +188,7 @@ int main(void) {
     afe_measure();
     tmp144_read_temps();
     check_error_conditions();
+    fan_ctrl_update();
     delay_period();
   }
   /* USER CODE END 3 */