diff --git a/ltr329.c b/ltr329.c
index 6918d7d..62f3869 100644
--- a/ltr329.c
+++ b/ltr329.c
@@ -5,7 +5,19 @@
  *      Author: david
  */
 #include "ltr329.h"
-#include "main.h" /* for uart_disable_interrupts() */
+
+/*
+ * Functions to be implemented by user
+ */
+
+/* I2C */
+int8_t ltr329_i2c_transmit(uint8_t address, uint8_t *buffer, int len) __attribute__((weak));
+int8_t ltr329_i2c_receive(uint8_t address, uint8_t *buffer, int len) __attribute__((weak)); 
+/* Interrupts */
+int8_t ltr329_disable_interrupts(void) __attribute__((weak));
+int8_t ltr329_enable_interrupts(void) __attribute__((weak));
+/* delay function */
+void delay_ms(int delay_ms) __attribute__((weak));
 
 static int8_t ltr329_read_register (ltr329_cmd_t register_addr, uint8_t *register_data )
 {
@@ -16,17 +28,17 @@ static int8_t ltr329_read_register (ltr329_cmd_t register_addr, uint8_t *registe
 	// start measurement
 	tx_buffer[0] = register_addr;
 	/* disable interrupts to prevent modbus/i2c conflict */
-	uart_disable_interrupts();
-	result = i2c_transmit(LTR329_I2C_ADDRESS<<1, tx_buffer, 1);
-	uart_enable_interrupts();
+	ltr329_disable_interrupts();
+	result = ltr329_i2c_transmit(LTR329_I2C_ADDRESS<<1, tx_buffer, 1);
+	ltr329_enable_interrupts();
 	if (result != I2C_OK) {
 		return LTR329_ERROR;
 	}
-	LL_mDelay(10); /* 10 ms should be enough */
+	delay_ms(10); /* 10 ms should be enough */
 	/* read out */
-	uart_disable_interrupts();
-	result = i2c_receive(LTR329_I2C_ADDRESS<<1, rx_buffer, 1);
-	uart_enable_interrupts();
+	ltr329_disable_interrupts();
+	result = ltr329_i2c_receive(LTR329_I2C_ADDRESS<<1, rx_buffer, 1);
+	ltr329_enable_interrupts();
 	if (result != I2C_OK) {
 		return LTR329_ERROR;
 	}
@@ -44,9 +56,9 @@ static int8_t ltr329_write_register (ltr329_cmd_t register_addr, uint8_t registe
 	tx_buffer[0] = register_addr;
 	tx_buffer[1] = register_data;
 	/* disable interrupts to prevent modbus/i2c conflict */
-	uart_disable_interrupts();
-	result = i2c_transmit(LTR329_I2C_ADDRESS<<1, tx_buffer, 2);
-	uart_enable_interrupts();
+	ltr329_disable_interrupts();
+	result = ltr329_i2c_transmit(LTR329_I2C_ADDRESS<<1, tx_buffer, 2);
+	ltr329_enable_interrupts();
 	if (result != I2C_OK) {
 		return LTR329_ERROR;
 	}