Expose serial number & device type properties

LICENSE

@@ -1,6 +1,6 @@
 The MIT License (MIT)
 
-Copyright (c) 2017 Radomir Dopieralski, written for Adafruit Industries
+Copyright (c) 2017 Radomir Dopieralski, written for Adafruit Industries, and (c) 2016 Chris Balmer
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal

adafruit_si7021.py

@@ -8,7 +8,7 @@
 
 This is a CircuitPython driver for the SI7021 temperature and humidity sensor.
 
-* Author(s): Radomir Dopieralski
+* Author(s): Radomir Dopieralski, Chris Balmer, Ian Grant
 
 Implementation Notes
 --------------------
@@ -40,6 +40,8 @@
 _RESET = const(0xFE)
 _READ_USER1 = const(0xE7)
 _USER1_VAL = const(0x3A)
+_ID1_CMD = bytearray([0xFA, 0x0F])
+_ID2_CMD = bytearray([0xFC, 0xC9])
 
 
 def _crc(data):
@@ -55,6 +57,36 @@ def _crc(data):
     return crc
 
 
+def _convert_to_integer(bytes_to_convert):
+    """Use bitwise operators to convert the bytes into integers."""
+    integer = None
+    for chunk in bytes_to_convert:
+        if not integer:
+            integer = chunk
+        else:
+            integer = integer << 8
+            integer = integer | chunk
+    return integer
+
+
+def _get_device_identifier(identifier_byte):
+    """
+    Convert the identifier byte to a device identifier (model type).
+    Values are based on the information from page 24 of the datasheet.
+    """
+    if identifier_byte in (0x00, 0xFF):
+        identifier_string = "Engineering sample"
+    elif identifier_byte == 0x0D:
+        identifier_string = "Si7013"
+    elif identifier_byte == 0x14:
+        identifier_string = "Si7020"
+    elif identifier_byte == 0x15:
+        identifier_string = "Si7021"
+    else:
+        identifier_string = "Unknown"
+    return identifier_string
+
+
 class SI7021:
     """
     A driver for the SI7021 temperature and humidity sensor.
@@ -141,3 +173,38 @@ def start_measurement(self, what):
         elif self._measurement != what:
             raise RuntimeError("other measurement in progress")
         self._measurement = what
+
+    @property
+    def serial_number(self):
+        """The device's unique ID (serial number)."""
+        return self._get_device_info()[0]
+
+    @property
+    def device_identifier(self):
+        """A device identifier (model type) string."""
+        return self._get_device_info()[1]
+
+    def _get_device_info(self):
+        """
+        Get the serial number and the sensor identifier (model type).
+        The identifier is part of the bytes returned for the serial number.
+        Source: https://github.com/chrisbalmer/micropython-si7021
+        """
+        # Serial 1st half
+        data = _ID1_CMD
+        id1 = bytearray(8)
+        with self.i2c_device as i2c:
+            i2c.write_then_readinto(data, id1)
+        # Serial 2nd half
+        data = _ID2_CMD
+        id2 = bytearray(6)
+        with self.i2c_device as i2c:
+            i2c.write_then_readinto(data, id2)
+        # Combine the two halves
+        combined_id = bytearray(
+            [id1[0], id1[2], id1[4], id1[6], id2[0], id2[1], id2[3], id2[4]]
+        )
+        # Convert serial number and extract identifier part
+        serial = _convert_to_integer(combined_id)
+        identifier = _get_device_identifier(id2[0])
+        return serial, identifier