diff --git a/app/include/user_modules.h b/app/include/user_modules.h
index d6d92f19..de910614 100644
--- a/app/include/user_modules.h
+++ b/app/include/user_modules.h
@@ -53,6 +53,7 @@
 //#define LUA_USE_MODULES_RTCFIFO
 //#define LUA_USE_MODULES_RTCMEM
 //#define LUA_USE_MODULES_RTCTIME
+//#define LUA_USE_MODULES_SI7021
 //#define LUA_USE_MODULES_SIGMA_DELTA
 //#define LUA_USE_MODULES_SJSON
 //#define LUA_USE_MODULES_SNTP
diff --git a/app/modules/si7021.c b/app/modules/si7021.c
new file mode 100644
index 00000000..fbcbebc4
--- /dev/null
+++ b/app/modules/si7021.c
@@ -0,0 +1,265 @@
+//***************************************************************************
+// Si7021 module for ESP8266 with nodeMCU
+// fetchbot @github
+// MIT license, http://opensource.org/licenses/MIT
+//***************************************************************************
+
+#include "module.h"
+#include "lauxlib.h"
+#include "platform.h"
+#include "osapi.h"
+
+//***************************************************************************
+// I2C ADDRESS DEFINITON
+//***************************************************************************
+
+#define SI7021_I2C_ADDRESS				(0x40)
+
+//***************************************************************************
+// COMMAND DEFINITON
+//***************************************************************************
+
+#define SI7021_CMD_MEASURE_RH_HOLD		(0xE5)
+#define SI7021_CMD_MEASURE_RH_NOHOLD	(0xF5)
+#define SI7021_CMD_MEASURE_TEMP_HOLD	(0xE3)
+#define SI7021_CMD_MEASURE_TEMP_NOHOLD	(0xF3)
+#define SI7021_CMD_READ_PREV_TEMP		(0xE0)
+#define SI7021_CMD_RESET				(0xFE)
+#define SI7021_CMD_WRITE_RHT_REG		(0xE6)
+#define SI7021_CMD_READ_RHT_REG			(0xE7)
+#define SI7021_CMD_WRITE_HEATER_REG		(0x51)
+#define SI7021_CMD_READ_HEATER_REG		(0x11)
+#define SI7021_CMD_ID1					(0xFA0F)
+#define SI7021_CMD_ID2					(0xFCC9)
+#define SI7021_CMD_FIRM_REV				(0x84B8)
+
+//***************************************************************************
+// REGISTER DEFINITON
+//***************************************************************************
+
+#define SI7021_RH12_TEMP14				(0x00)
+#define SI7021_RH08_TEMP12				(0x01)
+#define SI7021_RH10_TEMP13				(0x80)
+#define SI7021_RH11_TEMP11				(0x81)
+#define SI7021_HEATER_ENABLE			(0x04)
+#define SI7021_HEATER_DISABLE			(0x00)
+
+//***************************************************************************
+
+static const uint32_t si7021_i2c_id = 0;
+static uint8_t si7021_i2c_addr = SI7021_I2C_ADDRESS;
+static uint8_t si7021_res = 0x00;
+static uint8_t si7021_config = 0x3A;
+static uint8_t si7021_heater = 0x00;
+static uint8_t si7021_heater_setting = 0x00;
+
+static uint8_t write_byte(uint8_t reg) {
+	platform_i2c_send_start(si7021_i2c_id);
+	platform_i2c_send_address(si7021_i2c_id, si7021_i2c_addr, PLATFORM_I2C_DIRECTION_TRANSMITTER);
+	platform_i2c_send_byte(si7021_i2c_id, reg);
+	platform_i2c_send_stop(si7021_i2c_id);
+}
+
+static uint8_t write_reg(uint8_t reg, uint8_t data) {
+	platform_i2c_send_start(si7021_i2c_id);
+	platform_i2c_send_address(si7021_i2c_id, si7021_i2c_addr, PLATFORM_I2C_DIRECTION_TRANSMITTER);
+	platform_i2c_send_byte(si7021_i2c_id, reg);
+	platform_i2c_send_byte(si7021_i2c_id, data);
+	platform_i2c_send_stop(si7021_i2c_id);
+}
+
+static uint8_t read_reg(uint8_t reg, uint8_t *buf, uint8_t size) {
+	platform_i2c_send_start(si7021_i2c_id);
+	platform_i2c_send_address(si7021_i2c_id, si7021_i2c_addr, PLATFORM_I2C_DIRECTION_TRANSMITTER);
+	platform_i2c_send_byte(si7021_i2c_id, reg);
+	platform_i2c_send_stop(si7021_i2c_id);
+	platform_i2c_send_start(si7021_i2c_id);
+	platform_i2c_send_address(si7021_i2c_id, si7021_i2c_addr, PLATFORM_I2C_DIRECTION_RECEIVER);
+	os_delay_us(25000);
+	while (size-- > 0)
+		*buf++ = platform_i2c_recv_byte(si7021_i2c_id, size > 0);
+	platform_i2c_send_stop(si7021_i2c_id);
+	return 1;
+}
+
+static uint8_t read_serial(uint16_t reg, uint8_t *buf, uint8_t size) {
+	platform_i2c_send_start(si7021_i2c_id);
+	platform_i2c_send_address(si7021_i2c_id, si7021_i2c_addr, PLATFORM_I2C_DIRECTION_TRANSMITTER);
+	platform_i2c_send_byte(si7021_i2c_id, (uint8_t)(reg >> 8));
+	platform_i2c_send_byte(si7021_i2c_id, (uint8_t)(reg & 0xFF));
+	// platform_i2c_send_stop(si7021_i2c_id);
+	platform_i2c_send_start(si7021_i2c_id);
+	platform_i2c_send_address(si7021_i2c_id, si7021_i2c_addr, PLATFORM_I2C_DIRECTION_RECEIVER);
+	while (size-- > 0)
+		*buf++ = platform_i2c_recv_byte(si7021_i2c_id, size > 0);
+	platform_i2c_send_stop(si7021_i2c_id);
+	return 1;
+}
+
+// CRC8
+uint8_t si7021_crc8(uint8_t crc, uint8_t *buf, uint8_t size) {
+	while (size--) {
+		crc ^= *buf++;
+		for (uint8_t i = 0; i < 8; i++) {
+			if (crc & 0x80) {
+				crc = (crc << 1) ^ 0x31;
+			} else crc <<= 1;
+		}
+	}
+	return crc;
+}
+
+static int si7021_lua_setup(lua_State* L) {
+
+	write_byte(SI7021_CMD_RESET);
+	os_delay_us(50000);
+
+	// check for device on i2c bus
+	uint8_t buf_r[1];
+	read_reg(SI7021_CMD_READ_RHT_REG, buf_r, 1);
+	if (buf_r[0] != 0x3A)
+		return luaL_error(L, "found no device");
+
+	return 0;
+}
+
+// Change sensor settings and returns them
+// Lua: 	res, vdds, heater[, heater_set] = si7021.settings(RESOLUTION[,HEATER,HEATER_SETTING])
+static int si7021_lua_setting(lua_State* L) {
+
+	// check variable
+	if (!lua_isnumber(L, 1)) {
+		return luaL_error(L, "wrong arg range");
+	}
+
+	si7021_res = luaL_checkinteger(L, 1);
+	if (!((si7021_res == SI7021_RH12_TEMP14) || (si7021_res == SI7021_RH08_TEMP12) || (si7021_res == SI7021_RH10_TEMP13) || (si7021_res == SI7021_RH11_TEMP11))) {
+		return luaL_error(L, "Invalid argument: resolution");
+	}
+
+	si7021_config = (si7021_res | 0x3A);
+	write_reg(SI7021_CMD_WRITE_RHT_REG,si7021_config);
+
+	// Parse optional parameters
+	if (lua_isnumber(L, 2)) {
+
+		if (!lua_isnumber(L, 2) || !lua_isnumber(L, 3)) {
+			return luaL_error(L, "wrong arg range");
+		}
+
+		si7021_heater = luaL_checkinteger(L, 2);
+		if (!((si7021_heater == SI7021_HEATER_ENABLE) || (si7021_heater == SI7021_HEATER_DISABLE))) {
+			return luaL_error(L, "Invalid argument: heater");
+		}
+
+		si7021_heater_setting = luaL_checkinteger(L, 3);
+		if ((si7021_heater_setting < 0x00) || (si7021_heater_setting > 0x0F)) {
+			return luaL_error(L, "Invalid argument: heater_setting");
+		}
+
+		si7021_config = (si7021_res | si7021_heater | 0x3A);
+		write_reg(SI7021_CMD_WRITE_RHT_REG,si7021_config);
+		write_reg(SI7021_CMD_WRITE_HEATER_REG,(si7021_heater_setting & 0x0F));
+	}
+
+	uint8_t buf_c[1];
+	uint8_t buf_h[1];
+	read_reg(SI7021_CMD_READ_RHT_REG, buf_c, 1);
+	read_reg(SI7021_CMD_READ_HEATER_REG, buf_h, 1);
+
+	lua_pushinteger(L, ((buf_c[0] >> 6) + (buf_c[0] & 0x01)));
+	lua_pushinteger(L, ((buf_c[0] >> 6) & 0x01));
+	lua_pushinteger(L, ((buf_c[0] >> 2) & 0x01));
+	lua_pushinteger(L, (buf_h[0] & 0x0F));
+
+	return 4;
+}
+
+// Reads sensor values from device and returns them
+// Lua: 	hum, temp, humdec, tempdec = si7021.read()
+static int si7021_lua_read(lua_State* L) {
+
+	uint8_t buf_h[3];	// first two byte data, third byte crc
+	read_reg(SI7021_CMD_MEASURE_RH_HOLD, buf_h, 3);
+	if (buf_h[2] != si7021_crc8(0, buf_h, 2))	//crc check
+		return luaL_error(L, "crc error");
+	double hum = (uint16_t)((buf_h[0] << 8) | buf_h[1]);
+	hum = ((hum * 125) / 65536 - 6);
+	int humdec = (int)((hum - (int)hum) * 1000);
+
+	uint8_t buf_t[2];	// two byte data, no crc on combined temp measurement
+	read_reg(SI7021_CMD_READ_PREV_TEMP, buf_t, 2);
+	double temp = (uint16_t)((buf_t[0] << 8) | buf_t[1]);
+	temp = ((temp * 175.72) / 65536 - 46.85);
+	int tempdec = (int)((temp - (int)temp) * 1000);
+
+	lua_pushnumber(L, hum);
+	lua_pushnumber(L, temp);
+	lua_pushinteger(L, humdec);
+	lua_pushinteger(L, tempdec);
+
+	return 4;
+}
+
+// Reads electronic serial number from device and returns them
+// Lua: 	serial = si7021.serial()
+static int si7021_lua_serial(lua_State* L) {
+
+	uint32_t serial_a;
+	uint8_t crc = 0;
+	uint8_t buf_s_1[8];	// every second byte contains crc
+	read_serial(SI7021_CMD_ID1, buf_s_1, 8);
+	for(uint8_t i = 0; i <= 6; i+=2) {
+		crc = si7021_crc8(crc, buf_s_1+i, 1);
+		if (buf_s_1[i+1] != crc)
+			return luaL_error(L, "crc error");
+		serial_a = (serial_a << 8) + buf_s_1[i];
+	}
+
+	uint32_t serial_b;
+	crc = 0;
+	uint8_t buf_s_2[6]; // every third byte contains crc
+	read_serial(SI7021_CMD_ID2, buf_s_2, 6);
+	for(uint8_t i = 0; i <=3; i+=3) {
+		crc = si7021_crc8(crc, buf_s_2+i, 2);
+		if (buf_s_2[i+2] != crc)
+			return luaL_error(L, "crc error");
+		serial_b = (serial_b << 16) + (buf_s_2[i] << 8) + buf_s_2[i+1];
+	}
+
+	lua_pushinteger(L, serial_a);
+	lua_pushinteger(L, serial_b);
+
+	return 2;
+}
+
+// Reads electronic firmware revision from device and returns them
+// Lua: 	firmware = si7021.firmware()
+static int si7021_lua_firmware(lua_State* L) {
+
+	uint8_t firmware;
+	uint8_t buf_f[1];
+	read_serial(SI7021_CMD_FIRM_REV, buf_f, 1);
+	firmware = buf_f[0];
+
+	lua_pushinteger(L, firmware);
+
+	return 1;
+}
+
+static const LUA_REG_TYPE si7021_map[] = {
+	{	LSTRKEY( "setup" ),				LFUNCVAL(si7021_lua_setup)		},
+	{	LSTRKEY( "setting" ),			LFUNCVAL(si7021_lua_setting)	},
+	{	LSTRKEY( "read" ),				LFUNCVAL(si7021_lua_read)		},
+	{	LSTRKEY( "serial" ),			LFUNCVAL(si7021_lua_serial)		},
+	{	LSTRKEY( "firmware" ),			LFUNCVAL(si7021_lua_firmware)	},
+	{	LSTRKEY( "RH12_TEMP14" ),		LNUMVAL(SI7021_RH12_TEMP14)		},
+	{	LSTRKEY( "RH08_TEMP12" ),		LNUMVAL(SI7021_RH08_TEMP12)		},
+	{	LSTRKEY( "RH10_TEMP13" ),		LNUMVAL(SI7021_RH10_TEMP13)		},
+	{	LSTRKEY( "RH11_TEMP11" ),		LNUMVAL(SI7021_RH11_TEMP11)		},
+	{	LSTRKEY( "HEATER_ENABLE" ),		LNUMVAL(SI7021_HEATER_ENABLE)	},
+	{	LSTRKEY( "HEATER_DISABLE" ),	LNUMVAL(SI7021_HEATER_DISABLE)	},
+	{	LNILKEY, LNILVAL												}
+};
+
+NODEMCU_MODULE(SI7021, "si7021", si7021_map, NULL);
diff --git a/docs/en/modules/si7021.md b/docs/en/modules/si7021.md
new file mode 100644
index 00000000..fc406bf6
--- /dev/null
+++ b/docs/en/modules/si7021.md
@@ -0,0 +1,152 @@
+# Si7021 Module
+| Since  | Origin / Contributor  | Maintainer  | Source  |
+| :----- | :-------------------- | :---------- | :------ |
+| 2017-04-19 | [fetchbot](https://github.com/fetchbot) | [fetchbot](https://github.com/fetchbot) | [si7021.c](../../../app/modules/si7021.c)|
+
+This module provides access to the Si7021 humidity and temperature sensor.
+
+## si7021.firmware()
+Read the internal firmware revision of the Si7021 sensor.
+
+#### Syntax
+`si7021.firmware()`
+
+#### Parameters
+none
+
+#### Returns
+`fwrev` Firmware version
+* `0xFF` Firmware version 1.0
+* `0x20` Firmware version 2.0
+
+#### Example
+```lua
+local sda, scl = 6, 5
+i2c.setup(0, sda, scl, i2c.SLOW) -- call i2c.setup() only once
+si7021.setup()
+
+fwrev = si7021.firmware()
+print(string.format("FW: %X\r\n", fwrev))
+```
+
+## si7021.setting()
+Settings for the sensors configuration register to adjust measurement resolution, on-chip heater and read the supply voltage status.
+
+#### Syntax
+`si7021.setting(RESOLUTION[, HEATER, HEATER_SETTING])`
+
+#### Parameters
+- `RESOLUTION`
+	* `si7021.RH12_TEMP14` Relative Humidity 12 bit - Temperature 14 bit (default)
+	* `si7021.RH08_TEMP12` Relative Humidity 8 bit - Temperature 12 bit
+	* `si7021.RH10_TEMP13` Relative Humidity 10 bit - Temperature 13 bit
+	* `si7021.RH11_TEMP11` Relative Humidity 11 bit - Temperature 11 bit
+- `HEATER` optional
+	* `si7021.HEATER_ENABLE` On-chip Heater Enable
+	* `si7021.HEATER_DISABLE` On-chip Heater Disable (default)
+- `HEATER_SETTING` optional
+	* `0x00` - `0x0F` 3.09 mA - 94.20 mA
+
+#### Returns
+- `resolution`
+	* `0` Relative Humidity 12 bit - Temperature 14 bit
+	* `1` Relative Humidity 8 bit - Temperature 12 bit
+	* `2` Relative Humidity 10 bit - Temperature 13 bit
+	* `3` Relative Humidity 11 bit - Temperature 11 bit
+- `vdds`
+	* `0` VDD OK (1.9V - 3.6V)
+	* `1` VDD LOW (1.8V - 1.9V)
+- `heater`
+	* `0` Disabled
+	* `1` Enabled
+- `heater_setting`
+	* `0` - `15`
+
+#### Example
+```lua
+local id, sda, scl = 0, 6, 5
+i2c.setup(id, sda, scl, i2c.SLOW) -- call i2c.setup() only once
+si7021.setup()
+
+res, vdds, heater, heater_set = si7021.setting(si7021.RH12_TEMP14)
+res, vdds, heater, heater_set = si7021.setting(si7021.RH12_TEMP14, si7021.HEATER_ENABLE, 0x01)
+```
+
+## si7021.setup()
+Initializes the device on fixed I²C device address (0x40).
+
+#### Syntax
+`si7021.setup()`
+
+#### Parameters
+none
+
+#### Returns
+`nil`
+
+#### Example
+```lua
+local sda, scl = 6, 5
+i2c.setup(0, sda, scl, i2c.SLOW) -- call i2c.setup() only once
+si7021.setup()
+```
+
+## si7021.read()
+
+#### Syntax
+`si7021.read()`
+
+#### Parameters
+none
+
+#### Returns
+- `hum` humidity (see note below)
+- `temp` temperature (see note below)
+- `hum_dec` humidity decimal
+- `temp_dec` temperature decimal
+
+!!! note
+
+	If using float firmware then `hum` and `temp` are floating point numbers. On an integer firmware, the final values have to be concatenated from `hum` and `hum_dec` / `temp` and `temp_dec`.
+
+#### Example
+```lua
+local sda, scl = 6, 5
+i2c.setup(0, sda, scl, i2c.SLOW) -- call i2c.setup() only once
+si7021.setup()
+
+hum, temp, hum_dec, temp_dec = si7021.read()
+
+-- Integer firmware using this example
+print(string.format("Humidity:\t\t%d.%03d\nTemperature:\t%d.%03d\n", hum, hum_dec, temp, temp_dec))
+
+-- Float firmware using this example
+print("Humidity: "..hum.."\n".."Temperature: "..temp)
+```
+
+## si7021.serial()
+Read the individualized 64-bit electronic serial number of the Si7021 sensor.
+
+#### Syntax
+`si7021.serial()`
+
+#### Parameters
+none
+
+#### Returns
+- `sna` 32-bit serial number part a
+- `snb` 32-bit serial number part b, upper byte contains the device identification
+	* `0x00` or `0xFF` engineering samples
+	* `0x0D` `13` Si7013
+	* `0x14` `20` Si7020
+	* `0x15` `21` Si7021
+
+#### Example
+```lua
+local sda, scl = 6, 5
+i2c.setup(0, sda, scl, i2c.SLOW) -- call i2c.setup() only once
+si7021.setup()
+
+sna, snb = si7021.serial()
+print(string.format("SN:\t\t%X%X\nDevice:\tSi70%d", sna, snb, bit.rshift(snb,24)))
+```
diff --git a/mkdocs.yml b/mkdocs.yml
index c4d69c0c..c9909ae9 100644
--- a/mkdocs.yml
+++ b/mkdocs.yml
@@ -72,6 +72,7 @@ pages:
         - 'rtcfifo': 'en/modules/rtcfifo.md'
         - 'rtcmem': 'en/modules/rtcmem.md'
         - 'rtctime': 'en/modules/rtctime.md'
+        - 'si7021' : 'en/modules/si7021'
         - 'sigma delta': 'en/modules/sigma-delta.md'
         - 'sjson': 'en/modules/sjson.md'
         - 'sntp': 'en/modules/sntp.md'