diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..496ee2c
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+.DS_Store
\ No newline at end of file
diff --git a/include/zh_avr_ac_dimmer.h b/include/zh_avr_ac_dimmer.h
new file mode 100644
index 0000000..2dd9bc7
--- /dev/null
+++ b/include/zh_avr_ac_dimmer.h
@@ -0,0 +1,63 @@
+#pragma once
+
+// #include "FreeRTOS.h"
+// #include "semphr.h"
+#include "avr_err.h"
+#include "stdbool.h"
+#include "avr/interrupt.h"
+#include "avr/pgmspace.h"
+
+#define ZH_AVR_AC_DIMMER_INIT_CONFIG_DEFAULT() \
+    {                                          \
+        .task_priority = configMAX_PRIORITIES, \
+        .stack_size = 124,                     \
+        .queue_size = 1,                       \
+        .a_gpio_number = 0,                    \
+        .b_gpio_number = 0,                    \
+        .pullup = false,                       \
+        .encoder_min_value = -100,             \
+        .encoder_max_value = 100,              \
+        .encoder_step = 1,                     \
+        .encoder_number = 0}
+
+#ifdef __cplusplus
+extern "C"
+{
+#endif
+
+    typedef struct // Structure for initial initialization of AC dimmer.
+    {
+        uint8_t task_priority;  // Task priority for the PCF8574 expander isr processing. @note It is not recommended to set a value less than configMAX_PRIORITIES.
+        uint8_t stack_size;     // Stack size for task for the PCF8574 expander isr processing processing. @note The minimum size is 124 byte.
+        uint8_t i2c_address;    // Expander I2C address.
+        bool p0_gpio_work_mode; // Expander GPIO PO work mode. True for input, false for output.
+        bool p1_gpio_work_mode; // Expander GPIO P1 work mode. True for input, false for output.
+        bool p2_gpio_work_mode; // Expander GPIO P2 work mode. True for input, false for output.
+        bool p3_gpio_work_mode; // Expander GPIO P3 work mode. True for input, false for output.
+        bool p4_gpio_work_mode; // Expander GPIO P4 work mode. True for input, false for output.
+        bool p5_gpio_work_mode; // Expander GPIO P5 work mode. True for input, false for output.
+        bool p6_gpio_work_mode; // Expander GPIO P6 work mode. True for input, false for output.
+        bool p7_gpio_work_mode; // Expander GPIO P7 work mode. True for input, false for output.
+        uint8_t interrupt_gpio; // Interrupt GPIO. @attention Must be same for all PCF8574 expanders.
+        uint8_t interrupt_port; // Interrupt port.
+    } zh_avr_pcf8574_init_config_t;
+
+    /**
+     * @brief Initialize PCF8574 expander.
+     *
+     * @param[in] config Pointer to PCF8574 initialized configuration structure. Can point to a temporary variable.
+     * @param[out] handle Pointer to unique PCF8574 handle.
+     *
+     * @attention I2C driver must be initialized first.
+     *
+     * @note Before initialize the expander recommend initialize zh_avr_pcf8574_init_config_t structure with default values.
+     *
+     * @code zh_avr_pcf8574_init_config_t config = ZH_AVR_PCF8574_INIT_CONFIG_DEFAULT() @endcode
+     *
+     * @return AVR_OK if success or an error code otherwise.
+     */
+    avr_err_t zh_avr_pcf8574_init(const zh_avr_pcf8574_init_config_t *config, zh_avr_pcf8574_handle_t *handle);
+
+#ifdef __cplusplus
+}
+#endif
\ No newline at end of file
diff --git a/triac_400hz_delay.xlsx b/triac_400hz_delay.xlsx
new file mode 100644
index 0000000..aa41f37
Binary files /dev/null and b/triac_400hz_delay.xlsx differ
diff --git a/zh_avr_ac_dimmer.c b/zh_avr_ac_dimmer.c
new file mode 100644
index 0000000..7b5dbeb
--- /dev/null
+++ b/zh_avr_ac_dimmer.c
@@ -0,0 +1,12 @@
+#include "zh_avr_ac_dimmer.h"
+
+const static uint8_t _triac_400hz_delay[100] PROGMEM = {0, 155, 153, 152, 150, 148, 147, 145, 144, 142,
+                                                        141, 139, 137, 136, 134, 133, 131, 130, 128, 127,
+                                                        125, 123, 122, 120, 119, 117, 116, 114, 112, 111,
+                                                        109, 108, 106, 105, 103, 102, 100, 98, 97, 95,
+                                                        94, 92, 91, 89, 87, 86, 84, 83, 81, 80,
+                                                        78, 77, 75, 73, 72, 70, 69, 67, 66, 64,
+                                                        62, 61, 59, 58, 56, 55, 53, 52, 50, 48,
+                                                        47, 45, 44, 42, 41, 39, 37, 36, 34, 33,
+                                                        31, 30, 28, 27, 25, 23, 22, 20, 19, 17,
+                                                        16, 14, 12, 11, 9, 8, 6, 5, 3, 2};