diff --git a/fw/Core/Src/led.c b/fw/Core/Src/led.c
index 7914e04..0cc7f91 100644
--- a/fw/Core/Src/led.c
+++ b/fw/Core/Src/led.c
@@ -46,6 +46,22 @@ void led_set_color(uint8_t red, uint8_t green, uint8_t blue)
 	led_blue_intensity = (int)blue * led_pwm_max / 255;
 }
 
+void led_gpio_off(GPIO_TypeDef *port, uint32_t pin_mask)
+{
+	uint32_t port_value;
+	port_value = LL_GPIO_ReadInputPort(port);
+	port_value &= ~pin_mask;
+	LL_GPIO_WriteOutputPort(port, port_value);
+}
+
+void led_gpio_on(GPIO_TypeDef *port, uint32_t pin_mask)
+{
+	uint32_t port_value;
+	port_value = LL_GPIO_ReadInputPort(port);
+	port_value |= pin_mask;
+	LL_GPIO_WriteOutputPort(port, port_value);
+}
+
 /*
  * led_off():
  * Set LED intensity to 0 for each color
@@ -123,4 +139,8 @@ void led_init(led_context_t *context, int pwm_freq, int pwm_handler_freq)
 	// e.g. for 1 kHz handler freq and 25 Hz PWM freq, we only have
 	// resolution of 40 steps for pwm
 	led_pwm_max = pwm_handler_freq / pwm_freq;
+	// turn off all LEDs (inverted)
+	led_gpio_on(led_context->red_led_port, led_context->red_led_pin);
+	led_gpio_on(led_context->green_led_port, led_context->green_led_pin);
+	led_gpio_on(led_context->blue_led_port, led_context->blue_led_pin);
 }
diff --git a/fw/Core/Src/main.c b/fw/Core/Src/main.c
index 6007773..2b27a57 100644
--- a/fw/Core/Src/main.c
+++ b/fw/Core/Src/main.c
@@ -107,7 +107,7 @@ int main(void)
   led_context.green_led_pin = LED_G_Pin;
   led_context.blue_led_pin = LED_B_Pin;
   led_init(&led_context, 50, 1000);
-  led_set_color(80, 0, 0);
+  led_set_color(0, 20, 0);
   /* I2C context init (for SHT4x and SCD4x) */
   i2c_context_t i2c_context;
   i2c_context.i2c = I2C1;
@@ -120,7 +120,6 @@ int main(void)
   sht4x_measure(&T, &RH);
   while (1)
   {
-	led_pwm_handler(); // TODO temporary, should be placed in timer interrupt (SysTick)
     /* USER CODE END WHILE */
     /* USER CODE BEGIN 3 */
   }
diff --git a/fw/Core/Src/sht4x.c b/fw/Core/Src/sht4x.c
index 9f14b54..50521da 100644
--- a/fw/Core/Src/sht4x.c
+++ b/fw/Core/Src/sht4x.c
@@ -28,8 +28,7 @@ int sht4x_measure(int *temperature, int *relative_humidity)
 	if (result != I2C_OK) {
 		return SHT4X_ERROR;
 	}
-	// busy delay (LL_mDelay uses SysTick which doesn't work at the moment) TODO
-	for (volatile int j = 0; j < 100000; j++);
+	LL_mDelay(100); // 10 ms should be enough
 	// read out
 	result = i2c_receive(SHT4X_I2C_ADDRESS, buffer, 6);
 	if (result != I2C_OK) {
diff --git a/fw/Core/Src/stm32l0xx_it.c b/fw/Core/Src/stm32l0xx_it.c
index 9009e6d..063906f 100644
--- a/fw/Core/Src/stm32l0xx_it.c
+++ b/fw/Core/Src/stm32l0xx_it.c
@@ -131,7 +131,7 @@ void SysTick_Handler(void)
   /* USER CODE END SysTick_IRQn 0 */
 
   /* USER CODE BEGIN SysTick_IRQn 1 */
-//  led_pwm_handler();
+  led_pwm_handler();
   /* USER CODE END SysTick_IRQn 1 */
 }
 
diff --git a/fw/Drivers/STM32L0xx_HAL_Driver/Inc/stm32l0xx_ll_utils.h b/fw/Drivers/STM32L0xx_HAL_Driver/Inc/stm32l0xx_ll_utils.h
index 129bd8b..e6861f0 100644
--- a/fw/Drivers/STM32L0xx_HAL_Driver/Inc/stm32l0xx_ll_utils.h
+++ b/fw/Drivers/STM32L0xx_HAL_Driver/Inc/stm32l0xx_ll_utils.h
@@ -223,6 +223,7 @@ __STATIC_INLINE void LL_InitTick(uint32_t HCLKFrequency, uint32_t Ticks)
   SysTick->LOAD  = (uint32_t)((HCLKFrequency / Ticks) - 1UL);  /* set reload register */
   SysTick->VAL   = 0UL;                                       /* Load the SysTick Counter Value */
   SysTick->CTRL  = SysTick_CTRL_CLKSOURCE_Msk |
+		  	  	   SysTick_CTRL_TICKINT_Msk |
                    SysTick_CTRL_ENABLE_Msk;                   /* Enable the Systick Timer */
 }