Added HowToUseOtherDevice

HowToUseOtherDevice/README.md

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+# How to use other i2c devive at same time
+If you want to use SSD1306 and other i2c devices at the same time, please follow the guide below.   
+
+## Case 1
+Use multiple i2c devices on one i2c bus.   
+```
+I2C_NUM_0 --+-- I2C SSD1306
+            +---Any I2C Device
+```
+
+- Legacy driver
+
+We only need to run this code once.
+There is no need to memorize any data.
+DS3231 and SSD1306 use the same frequency.
+```
+        i2c_config_t i2c_config = {
+            .mode = I2C_MODE_MASTER,
+            .sda_io_num = sda,
+            .scl_io_num = scl,
+            .sda_pullup_en = GPIO_PULLUP_ENABLE,
+            .scl_pullup_en = GPIO_PULLUP_ENABLE,
+            .master.clk_speed = I2C_MASTER_FREQ_HZ
+        };
+        ESP_ERROR_CHECK(i2c_param_config(I2C_NUM, &i2c_config));
+        ESP_ERROR_CHECK(i2c_driver_install(I2C_NUM, I2C_MODE_MASTER, 0, 0, 0));
+```
+
+
+- New i2c driver
+
+We need to run this code on the first device.   
+**We need to record bus_handle somewhere.**
+But In different libraries, there is no place to record bus_handle.
+```
+    i2c_master_bus_config_t i2c_mst_config = {
+        .clk_source = I2C_CLK_SRC_DEFAULT,
+        .glitch_ignore_cnt = 7,
+        .i2c_port = I2C_NUM,
+        .scl_io_num = scl,
+        .sda_io_num = sda,
+        .flags.enable_internal_pullup = true,
+    };
+    i2c_master_bus_handle_t bus_handle;
+    ESP_ERROR_CHECK(i2c_new_master_bus(&i2c_mst_config, &bus_handle));
+
+    i2c_device_config_t dev_cfg = {
+        .dev_addr_length = I2C_ADDR_BIT_LEN_7,
+        .device_address = I2C_ADDRESS1,
+        .scl_speed_hz = I2C_MASTER_FREQ_HZ1,
+    };
+    i2c_master_dev_handle_t dev_handle;
+    ESP_ERROR_CHECK(i2c_master_bus_add_device(bus_handle, &dev_cfg, &dev_handle));
+
+    // We need to record bus_handle somewhere.
+```
+
+We need to run this code on the second device.
+**We need to load bus_handle from somewhere.**
+DS3231 and SSD1306 can use different frequencies.
+
+```
+    // We need to load bus_handle from somewhere.
+
+    i2c_device_config_t dev_cfg = {
+        .dev_addr_length = I2C_ADDR_BIT_LEN_7,
+        .device_address = I2C_ADDRESS2,
+        .scl_speed_hz = I2C_MASTER_FREQ_HZ2,
+    };
+    i2c_master_dev_handle_t dev_handle;
+    ESP_ERROR_CHECK(i2c_master_bus_add_device(bus_handle, &dev_cfg, &dev_handle));
+```
+
+---
+
+## Case 2
+Use multiple i2c devices on two i2c bus.   
+
+This is the only way to use different I2C libraries at the same time using the new i2c driver.
+ESP32C series has only one i2c bus.
+This is not available on the ESP32C series.
+Can only be used with XTENSA.
+
+```
+I2C_NUM_0 ----- I2C SSD1306
+I2C_NUM_1 ----- Any I2C Device
+```
+