Merge pull request pycom#44 from pycom/features/PYFW-64-Pysense-temperature-sensor-dew-point

Updated SI7006 temperature sensor lib with dew point computation

Author: catalinio

pysense/.DS_Store

@@ -1,8 +1,17 @@
 import time
 from machine import I2C
+import math
+
+__version__ = '0.0.2'
 
 class SI7006A20:
+    """ class for handling the temperature sensor SI7006-A20
+        +/- 1 deg C error for temperature
+        +/- 5% error for relative humidity
+        datasheet available at https://www.silabs.com/documents/public/data-sheets/Si7006-A20.pdf """
+
     SI7006A20_I2C_ADDR = const(0x40)
+
     TEMP_NOHOLDMASTER = const(0xF3)
     HUMD_NOHOLDMASTER = const(0xF5)
 
@@ -16,17 +25,84 @@ def _getWord(self, high, low):
         return ((high & 0xFF) << 8) + (low & 0xFF)
 
     def temperature(self):
+        """ obtaining the temperature(degrees Celsius) measured by sensor """
         self.i2c.writeto(SI7006A20_I2C_ADDR, bytearray([0xF3]))
         time.sleep(0.5)
-        data = self.i2c.readfrom(SI7006A20_I2C_ADDR, 2)
+        data = self.i2c.readfrom(SI7006A20_I2C_ADDR, 3)
+        #print("CRC Raw temp data: " + hex(data[0]*65536 + data[1]*256 + data[2]))
         data = self._getWord(data[0], data[1])
         temp = ((175.72 * data) / 65536.0) - 46.85
         return temp
 
     def humidity(self):
+        """ obtaining the relative humidity(%) measured by sensor """
         self.i2c.writeto(SI7006A20_I2C_ADDR, bytearray([0xF5]))
         time.sleep(0.5)
         data = self.i2c.readfrom(SI7006A20_I2C_ADDR, 2)
         data = self._getWord(data[0], data[1])
         humidity = ((125.0 * data) / 65536.0) - 6.0
         return humidity
+
+    def read_user_reg(self):
+        """ reading the user configuration register """
+        self.i2c.writeto(SI7006A20_I2C_ADDR, bytearray([0xE7]))
+        time.sleep(0.5)
+        data = self.i2c.readfrom(SI7006A20_I2C_ADDR, 1)
+        return data[0]
+
+    def read_heater_reg(self):
+        """ reading the heater configuration register """
+        self.i2c.writeto(SI7006A20_I2C_ADDR, bytearray([0x11]))
+        time.sleep(0.5)
+        data = self.i2c.readfrom(SI7006A20_I2C_ADDR, 1)
+        return data[0]
+
+    def read_electronic_id(self):
+        """ reading electronic identifier """
+        self.i2c.writeto(SI7006A20_I2C_ADDR, bytearray([0xFA]) + bytearray([0x0F]))
+        time.sleep(0.5)
+        sna = self.i2c.readfrom(SI7006A20_I2C_ADDR, 4)
+        time.sleep(0.1)
+        self.i2c.writeto(SI7006A20_I2C_ADDR, bytearray([0xFC]) + bytearray([0xC9]))
+        time.sleep(0.5)
+        snb = self.i2c.readfrom(SI7006A20_I2C_ADDR, 4)
+        return [sna[0], sna[1], sna[2], sna[3], snb[0], snb[1], snb[2], snb[3]]
+
+    def read_firmware(self):
+        """ reading firmware version """
+        self.i2c.writeto(SI7006A20_I2C_ADDR, bytearray([0x84])+ bytearray([0xB8]))
+        time.sleep(0.5)
+        fw = self.i2c.readfrom(SI7006A20_I2C_ADDR, 1)
+        return fw[0]
+
+    def read_reg(self, reg_addr):
+        """ reading a register """
+        self.i2c.writeto(SI7006A20_I2C_ADDR, bytearray([reg_addr]))
+        time.sleep(0.5)
+        data = self.i2c.readfrom(SI7006A20_I2C_ADDR, 1)
+        return data[0]
+
+    def write_reg(self, reg_addr, value):
+        """ writing a register """
+        self.i2c.writeto(SI7006A20_I2C_ADDR, bytearray([reg_addr])+bytearray([value]))
+        time.sleep(0.1)
+
+    def dew_point(self):
+        """ computing the dew pointe temperature (deg C) for the current Temperature and Humidity measured pair
+            at dew-point temperature the relative humidity is 100% """
+        temp = self.temperature()
+        humid = self.humidity()
+        h = (math.log(humid, 10) - 2) / 0.4343 + (17.62 * temp) / (243.12 + temp)
+        dew_p = 243.12 * h / (17.62 - h)
+        return dew_p
+
+    def humid_ambient(self, t_ambient, dew_p = None):
+        """ returns the relative humidity compensated for the current Ambient temperature
+            for ex: T-Ambient is 24.4 degC, but sensor indicates Temperature = 31.65 degC and Humidity = 47.3%
+                    -> then the actual Relative Humidity is 72.2%
+            this is computed because the dew-point should be the same """
+        if dew_p is None:
+            dew_p = self.dew_point()
+        h = 17.62 * dew_p / (243.12 + dew_p)
+        h_ambient = math.pow(10, (h - (17.62 * t_ambient) / (243.12 + t_ambient)) * 0.4343 + 2)
+        return h_ambient

pysense/lib/SI7006A20.py

@@ -12,15 +12,20 @@
 lt = LTR329ALS01(py)
 li = LIS2HH12(py)
 
-print(mp.temperature())
-print(mp.altitude())
+print("MPL3115A2 temperature: " + str(mp.temperature()))
+print("Altitude: " + str(mp.altitude()))
 mpp = MPL3115A2(py,mode=PRESSURE) # Returns pressure in Pa. Mode may also be set to ALTITUDE, returning a value in meters
-print(mpp.pressure())
-print(si.temperature())
-print(si.humidity())
-print(lt.light())
-print(li.acceleration())
-print(li.roll())
-print(li.pitch())
+print("Pressure: " + str(mpp.pressure()))
 
-print(py.read_battery_voltage())
+print("Temperature: " + str(si.temperature())+ " deg C and Relative Humidity: " + str(si.humidity()) + " %RH")
+print("Dew point: "+ str(si.dew_point()) + " deg C")
+t_ambient = 24.4
+print("Humidity Ambient for " + str(t_ambient) + " deg C is " + str(si.humid_ambient(t_ambient)) + "%RH")
+
+print("Light (channel Blue lux, channel Red lux): " + str(lt.light()))
+
+print("Acceleration: " + str(li.acceleration()))
+print("Roll: " + str(li.roll()))
+print("Pitch: " + str(li.pitch()))
+
+print("Battery voltage: " + str(py.read_battery_voltage()))