drivers/sensor/sht: Add driver for SHT3x/SHT4x sensors

Author: yvo64

micropython/drivers/sensor/sht/manifest.py

@@ -0,0 +1,3 @@
+metadata(description="SHT3x/SHT4x temperature/humidity sensor driver.", version="0.1.0")
+
+module("sht.py", opt=3)

micropython/drivers/sensor/sht/sht.py

@@ -0,0 +1,122 @@
+# Micropython driver for temperature/humidity sensors SHT3x/SHT4x
+#
+# Example usage on picoboard:
+# @code{.py}
+#    from machine import Pin, I2C
+#    from sht import SHT
+#    import time
+#    i2c = I2C(0, scl=Pin(5), sda=Pin(4))
+#    sensor = SHT(i2c)
+#    sensor.start_measure(2)
+#    while True:
+#        time.sleep(0.01)
+#        t_raw, t_val, h_raw, h_val, isvalid = sensor.get_measure_results()
+#        if isvalid is not None:
+#            break
+#    print(f'{t_raw}, {t_val} °C, {h_raw}, {h_val} %RH, isvalid')
+# @endcode
+#
+
+from machine import I2C
+import time
+
+
+class SHT:
+
+    SHT3x = (0x30)
+    SHT4x = (0x40)
+
+    # Init SHT
+    # @param i2c  I2C interface
+    # @param addr I2C addr (default = 0x44)
+    # @param sht  SHT type
+    #             0x00 (autodetect SHT type)
+    #             self.SHT3x
+    #             self.SHT4x
+    def __init__(self, i2c, addr=0x44, sht=0x00):
+        self.i2c = i2c
+        self.i2c_addr = addr
+        self.sht = sht
+        if self.sht == 0x00:
+            self.sht = self.detect_sht_type()
+        else:
+            self.sht = sht
+
+    # Verify checksum
+    # @param data     data bytes
+    # @param checksum received crc
+    # @return crc status
+    #     0 = crc does not match
+    #     1 = crc ok
+    def _check_crc(self, data, checksum):
+        crc = 0xFF
+        for byte in data:
+            crc ^= byte
+            for _ in range(8):
+                if crc & 0x80:
+                    crc = (crc << 1) ^ 0x31
+                else:
+                    crc = crc << 1
+        crc = crc & 0xFF
+        return checksum == crc
+
+    # Autodetect SHT type
+    # @return SHT type
+    #     self.SHT3x = SHT30/31/35
+    #     self.SHT4x = SHT40/41/45
+    #     0xFF = unknown
+    def detect_sht_type(self):
+        sht = 0xFF
+        # try reading status of SHT3x
+        try:
+            self.i2c.writeto(self.i2c_addr, b'\xF3\x2D', False)
+            time.sleep(0.01)
+            response = self.i2c.readfrom(self.i2c_addr, 3)
+            if self._check_crc(response[0:2],response[2]):
+                sht = self.SHT3x
+        except OSError as error :
+            pass
+        if sht == 0xFF:
+            # try reading serial number of SHT4x
+            try:
+                self.i2c.writeto(self.i2c_addr, b'\x89', False)
+                time.sleep(0.01)
+                response = self.i2c.readfrom(self.i2c_addr, 6)
+                if self._check_crc(response[3:5],response[5]):
+                    sht = self.SHT4x
+            except OSError as error :
+                pass
+        return sht
+
+    # Start measurement
+    # @param precision 0..2 [Low, Medlium, High]
+    # @return None
+    def start_measure(self, precision):
+        if self.sht == self.SHT3x:
+            p_byte = [b'\x16',b'\x0B',b'\x00']
+            self.i2c.writeto(self.i2c_addr, b'\x24' + p_byte[precision], False)
+        if self.sht == self.SHT4x:
+            cmd = [b'\xE0',b'\xF6',b'\xFD']
+            self.i2c.writeto(self.i2c_addr, cmd[precision], False)
+
+    # Get the measurement values
+    # @details
+    #   As long as no values available all return parameter are None.
+    #   If values not equal None are returned the measurement has been completed
+    #   and needs to be restarted again for a new measurement.
+    # @return temperature[raw], temperature[°C], humidity[raw], humidity[%RH]
+    def get_measure_results(self):
+        try:
+            response = self.i2c.readfrom(self.i2c_addr, 6)
+            t_bytes = response[0:2]
+            t_raw = int.from_bytes(t_bytes, "big")
+            t_val = (175 * t_raw) / 0xFFFF - 45
+            isvalid = self._check_crc(t_bytes,response[2])
+            h_bytes = response[3:5]
+            h_raw = int.from_bytes(h_bytes, "big")
+            h_val = (100 * h_raw) / 0xFFFF
+            isvalid &= self._check_crc(h_bytes,response[5])
+            return t_raw, round(t_val,2), h_raw, round(h_val,2), bool(isvalid)
+        except OSError as error :
+            # OSError: [Errno 5] EIO as long as measurement has not completed
+            return None, None, None, None, None