Add support for HTU21D/SHT21 temperature and humidity sensors

app/include/user_modules.h

@@ -42,6 +42,7 @@
 //#define LUA_USE_MODULES_HDC1080
 //#define LUA_USE_MODULES_HMC5883L
 //#define LUA_USE_MODULES_HTTP
+//#define LUA_USE_MODULES_HTU21
 //#define LUA_USE_MODULES_HX711
 #define LUA_USE_MODULES_I2C
 //#define LUA_USE_MODULES_L3G4200D

app/modules/htu21.c

@@ -0,0 +1,101 @@
+/*
+ * Driver for HTU21D/SHT21 humidity/temperature sensor.
+ *
+ */
+#include "module.h"
+#include "lauxlib.h"
+#include "platform.h"
+
+#define HTU21_ADDRESS           0x40
+/* HTU21 Commands */
+#define HTU21_T_MEASUREMENT_HM    0xE3
+#define HTU21_RH_MEASUREMENT_HM    0xE5
+#define HTU21_CRC_ERROR (uint16_t) 1
+
+//Give this function the 2 byte message (measurement) and the check_value byte from the HTU21D
+//If it returns 0, then the transmission was good
+//If it returns something other than 0, then the communication was corrupted
+//From: http://www.nongnu.org/avr-libc/user-manual/group__util__crc.html
+//POLYNOMIAL = 0x0131 = x^8 + x^5 + x^4 + 1 : http://en.wikipedia.org/wiki/Computation_of_cyclic_redundancy_checks
+#define SHIFTED_DIVISOR 0x988000 //This is the 0x0131 polynomial shifted to farthest left of three bytes
+
+static inline int32_t htu21_temp_ticks_to_millicelsius(uint32_t ticks)
+{
+  ticks &= ~0x0003; /* clear status bits */
+  /*
+   * Formula T = -46.85 + 175.72 * ST / 2^16 from datasheet p14,
+   * optimized for integer fixed point (3 digits) arithmetic
+   */
+  return ((21965 * ticks) >> 13) - 46850;
+}
+
+static inline int32_t htu21_rh_ticks_to_per_cent_mille(uint32_t ticks)
+{
+  ticks &= ~0x0003; /* clear status bits */
+  /*
+   * Formula RH = -6 + 125 * SRH / 2^16 from datasheet p14,
+   * optimized for integer fixed point (3 digits) arithmetic
+   */
+  return ((15625 * ticks) >> 13) - 6000;
+}
+
+static uint8_t checkCRC(uint16_t ravValue, uint8_t checksum)
+{
+  uint32_t remainder = (uint32_t) ravValue << 8; //Pad with 8 bits because we have to add in the check value
+  remainder |= checksum; //Add on the check value
+
+  uint32_t divsor = (uint32_t) SHIFTED_DIVISOR;
+
+  //Operate on only 16 positions of max 24. The remaining 8 are our remainder and should be zero when we're done.
+  for (int i = 0; i < 16; i++)
+  {
+    if (remainder & (uint32_t) 1 << (23 - i)) //Check if there is a one in the left position
+      remainder ^= divsor;
+
+    divsor >>= 1; //Rotate the divsor max 16 times so that we have 8 bits left of a remainder
+  }
+
+  return (uint8_t) remainder;
+}
+
+static uint16_t read_with_crc_check(lua_State *L, uint8_t reg)
+{
+  uint16_t rawValue;
+  uint8_t checksum;
+
+  platform_i2c_send_start(0);
+  platform_i2c_send_address(0, HTU21_ADDRESS, PLATFORM_I2C_DIRECTION_TRANSMITTER);
+  platform_i2c_send_byte(0, reg);
+  platform_i2c_send_start(0);
+  platform_i2c_send_address(0, HTU21_ADDRESS, PLATFORM_I2C_DIRECTION_RECEIVER);
+
+  rawValue = (uint16_t) platform_i2c_recv_byte(0, 1) << 8;
+  rawValue |= platform_i2c_recv_byte(0, 1);
+  checksum = (uint8_t) platform_i2c_recv_byte(0, 0);
+
+  platform_i2c_send_stop(0);
+
+  return checkCRC(rawValue, checksum) != 0 ? HTU21_CRC_ERROR : rawValue;
+}
+
+static int htu21_read(lua_State *L)
+{
+  uint16_t rawT = read_with_crc_check(L, HTU21_T_MEASUREMENT_HM);
+  uint16_t rawRH = read_with_crc_check(L, HTU21_RH_MEASUREMENT_HM);
+
+  if (rawT == HTU21_CRC_ERROR || rawRH == HTU21_CRC_ERROR) {
+    luaL_error(L, "htu21 invalid CRC");
+  }
+
+  lua_pushinteger(L, htu21_temp_ticks_to_millicelsius(rawT));
+  lua_pushinteger(L, htu21_rh_ticks_to_per_cent_mille(rawRH));
+
+  return 2;
+}
+
+static const LUA_REG_TYPE htu21_map[] = {
+    {LSTRKEY("read"), LFUNCVAL(htu21_read)},
+    {LNILKEY, LNILVAL}
+};
+
+NODEMCU_MODULE(HTU21, "htu21", htu21_map, NULL);

docs/en/modules/htu21.md

@@ -0,0 +1,25 @@
+# HTU21 Module
+| Since  | Origin / Contributor  | Maintainer  | Source  |
+| :----- | :-------------------- | :---------- | :------ |
+| 2017-02-03 | [Pawel Switalski](https://github.com/s-pw) | [Pawel Switalski](https://github.com/s-pw) | [htu21.c](../../../app/modules/htu21.c)|
+
+
+This module provides access to the [HTU21D](https://www.sparkfun.com/products/13763) temperature and humidity sensor. The module also works with SHT21.
+
+## htu21.read()
+Samples the sensor then returns temperature and humidity value.
+
+#### Syntax
+`htu21.read()`
+
+#### Returns
+Temperature data in millidegree Celsius and humidity data in per cent mille
+
+#### Example
+```lua
+local sda, scl = 1, 2
+i2c.setup(0, sda, scl, i2c.SLOW)  -- call i2c.setup() only once
+local temperature, humidity = htu21.read()
+print(temperature / 1000 .. '°C')
+print(humidity / 1000 .. '%')
+```

mkdocs.yml

@@ -59,6 +59,7 @@ pages:
         - 'hdc1080': 'en/modules/hdc1080.md'
         - 'hmc5883l': 'en/modules/hmc5883l.md'
         - 'http': 'en/modules/http.md'
+        - 'htu21': 'en/modules/htu21.md'
         - 'hx711' : 'en/modules/hx711.md'
         - 'i2c' : 'en/modules/i2c.md'
         - 'l3g4200d' : 'en/modules/l3g4200d.md'