UART fixes

adafruit_pm25.py

@@ -149,8 +149,8 @@ def _read_into_buffer(self):
         with self.i2c_device as i2c:
             try:
                 i2c.readinto(self._buffer)
-            except OSError:
-                raise RuntimeError("Unable to read from PM2.5 over I2C")
+            except OSError as err:
+                raise RuntimeError("Unable to read from PM2.5 over I2C") from err
 
 
 class PM25_UART(PM25):
@@ -169,6 +169,24 @@ def __init__(self, uart, reset_pin=None):
             time.sleep(1)
 
         self._uart = uart
+        # Set PM2.5 to active mode via UART command
+        self._uart.write([0x42, 0x4D, 0xE1, 0x00, 0x01, 0x01, 0x71])
+        # Check mode change response
+        r = self._uart.read(8)
+        if (len(r) == 8) and (r[0] == 0x42) and (r[1] == 0x4D):
+            if sum(r[0:6]) == struct.unpack(">H", r[6:8])[0]:
+                # print("UART active mode configured successfully")
+                time.sleep(0.1)
+            else:
+                raise RuntimeError(
+                    "Error configuring PM2.5 sensor for active reading, \
+                    checksum failure on mode change response"
+                )
+        else:
+            raise RuntimeError(
+                "Error configuring PM2.5 sensor for active reading, \
+                malformed mode change response"
+            )
         super().__init__()
 
     def _read_into_buffer(self):
@@ -186,3 +204,64 @@ def _read_into_buffer(self):
         for i in range(31):
             self._buffer[i + 1] = remain[i]
         # print([hex(i) for i in self._buffer])
+
+
+class PM25_UART_PASSIVE(PM25):
+    """
+    A driver for the PM2.5 air quality sensor over UART in passive mode
+    """
+
+    def __init__(self, uart, reset_pin=None, enable_pin=None):
+        # Reset enable pin, if present
+        if enable_pin:
+            enable_pin.direction = Direction.OUTPUT
+            enable_pin.value = False
+            time.sleep(0.1)
+            enable_pin.value = True
+            time.sleep(1)
+
+        if reset_pin:
+            reset_pin.direction = Direction.OUTPUT
+            reset_pin.value = False
+            time.sleep(0.01)
+            reset_pin.value = True
+            time.sleep(1)
+
+        self._uart = uart
+        # Set PM2.5 to passive mode via UART command
+        self._uart.write([0x42, 0x4D, 0xE1, 0x00, 0x00, 0x01, 0x70])
+        # Check mode change response
+        r = self._uart.read(8)
+        if (len(r) == 8) and (r[0] == 0x42) and (r[1] == 0x4D):
+            if sum(r[0:6]) == struct.unpack(">H", r[6:8])[0]:
+                # print("UART passive mode configured successfully")
+                time.sleep(0.1)
+            else:
+                raise RuntimeError(
+                    "Error configuring PM2.5 sensor for active reading, \
+                    checksum failure on mode change response"
+                )
+        else:
+            raise RuntimeError(
+                "Error configuring PM2.5 sensor for passive reading, \
+                malformed mode change response"
+            )
+        time.sleep(0.2)
+        super().__init__()
+
+    def _read_into_buffer(self):
+        self._uart.flushInput()
+        # Request data from PM2.5 via UART command
+        self._uart.write([0x42, 0x4D, 0xE2, 0x00, 0x00, 0x01, 0x71])
+        b = self._uart.read(32)
+        if (len(b) == 32) and (b[0] == 0x42) and (b[1] == 0x4D):
+            self._buffer = b
+        elif len(b) <= 8:
+            time.sleep(0.1)
+            self._uart.flushInput()
+            self._uart.write([0x42, 0x4D, 0xE2, 0x00, 0x00, 0x01, 0x71])
+            b = self._uart.read(32)
+            if (len(b) == 32) and (b[0] == 0x42) and (b[1] == 0x4D):
+                self._buffer(b)
+            else:
+                raise RuntimeError("Unable to read from PM2.5 (incomplete frame)")

examples/pm25_simpletest.py

@@ -35,6 +35,15 @@
 # Connect to a PM2.5 sensor over UART
 # pm25 = adafruit_pm25.PM25_UART(uart, reset_pin)
 
+# Connect to a PM2.5 sensor over UART in passive mode on Enviro+ Hat on RPi
+# enable_pin = DigitalInOut(board.D27)
+# enable_pin.direction = Direction.OUTPUT
+# reset_pin = DigitalInOut(board.D22)
+# reset_pin.direction = Direction.OUTPUT
+# import serial
+# uart = serial.Serial("/dev/ttyAMA0", baudrate=9600, stopbits=1, parity="N", timeout=4)
+# pm25 = adafruit_pm25.PM25_UART_PASSIVE(uart, pin)
+
 # Create library object, use 'slow' 100KHz frequency!
 i2c = busio.I2C(board.SCL, board.SDA, frequency=100000)
 # Connect to a PM2.5 sensor over I2C