add raspberry pi and other fast-gpio device support when no pulseio

adafruit_dht.py

@@ -30,12 +30,14 @@
 
 import array
 import time
+from digitalio import DigitalInOut, Pull, Direction
+_USE_PULSEIO = False
 try:
     import pulseio
-except ImportError as excpt:
-    print("adafruit_dht requires the pulseio library, but it failed to load."+
-          "  Note that CircuitPython does not support pulseio on all boards.")
-    raise excpt
+    _USE_PULSEIO = True
+except ImportError:
+    pass   # This is OK, we'll try to bitbang it!
+
 
 __version__ = "0.0.0-auto.0"
 __repo__ = "https://github.com/adafruit/Adafruit_CircuitPython_DHT.git"
@@ -101,30 +103,50 @@ def _get_pulses(self):
         """
         pulses = array.array('H')
 
-        # create the PulseIn object using context manager
-        with pulseio.PulseIn(self._pin, 81, True) as pulse_in:
-
-            # The DHT type device use a specialize 1-wire protocol
-            # The microprocessor first sends a LOW signal for a
-            # specific length of time.  Then the device sends back a
-            # series HIGH and LOW signals.  The length the HIGH signals
-            # represents the device values.
-            pulse_in.pause()
-            pulse_in.clear()
-            pulse_in.resume(self._trig_wait)
-
-            # loop until we get the return pulse we need or
-            # time out after 1/4 second
-            tmono = time.monotonic()
-            while True:
-                if time.monotonic()-tmono > 0.25: # time out after 1/4 seconds
-                    break
-
-            pulse_in.pause()
-            while pulse_in:
-                pulses.append(pulse_in.popleft())
-            pulse_in.resume()
-
+        if _USE_PULSEIO:
+            # create the PulseIn object using context manager
+            with pulseio.PulseIn(self._pin, 81, True) as pulse_in:
+
+                # The DHT type device use a specialize 1-wire protocol
+                # The microprocessor first sends a LOW signal for a
+                # specific length of time.  Then the device sends back a
+                # series HIGH and LOW signals.  The length the HIGH signals
+                # represents the device values.
+                pulse_in.pause()
+                pulse_in.clear()
+                pulse_in.resume(self._trig_wait)
+
+                # loop until we get the return pulse we need or
+                # time out after 1/4 second
+                tmono = time.monotonic()
+                while time.monotonic() - tmono > 0.25:
+                    pass # time out after 1/4 seconds
+                pulse_in.pause()
+                while pulse_in:
+                    pulses.append(pulse_in.popleft())
+                pulse_in.resume()
+        else:
+            with DigitalInOut(self._pin) as dhtpin:
+                # we will bitbang if no pulsein capability
+                transitions = []
+                # Signal by setting pin high, then low, and releasing
+                dhtpin.direction = Direction.OUTPUT
+                dhtpin.value = True
+                time.sleep(0.1)
+                dhtpin.value = False
+                time.sleep(0.001)
+
+                timestamp = time.monotonic() # take timestamp
+                dhtval = True   # start with dht pin true because its pulled up
+                dhtpin.direction = Direction.INPUT
+                dhtpin.pull = Pull.UP
+                while time.monotonic() - timestamp < 0.1:
+                    if dhtval != dhtpin.value:
+                        dhtval = not dhtval  # we toggled
+                        transitions.append(time.monotonic()) # save the timestamp
+                # convert transtions to microsecond delta pulses:
+                for i in range(1, len(transitions)):
+                    pulses.append(int(1000000 * (transitions[i] - transitions[i-1])))
         return pulses
 
     def measure(self):
@@ -135,13 +157,12 @@ def measure(self):
             Raises RuntimeError exception for checksum failure and for insuffcient
             data returned from the device (try again)
         """
-        delay_between_readings = 0.5
-        if self._dht11:
-            delay_between_readings = 1.0
+        delay_between_readings = 2  # 2 seconds per read according to datasheet
         if time.monotonic()-self._last_called > delay_between_readings:
             self._last_called = time.monotonic()
 
             pulses = self._get_pulses()
+            #print(len(pulses), "pulses:", [x for x in pulses])
 
             if len(pulses) >= 80:
                 buf = array.array('B')
@@ -176,9 +197,12 @@ def measure(self):
                     # check sum failed to validate
                     raise RuntimeError("Checksum did not validate. Try again.")
 
-            else:
+            elif len(pulses) >= 10:
+                # We got *some* data just not 81 bits
                 raise RuntimeError("A full buffer was not returned.  Try again.")
-
+            else:
+                # Probably a connection issue!
+                raise RuntimeError("DHT sensor not found, check wiring")
     @property
     def temperature(self):
         """ temperature current reading.  It makes sure a reading is available

examples/dht_simpletest.py

@@ -1,18 +1,21 @@
 import time
-from board import D2
+import board
 import adafruit_dht
 
-#initial the dht device
-dhtDevice = adafruit_dht.DHT22(D2)
+# Initial the dht device, with data pin connected to:
+dhtDevice = adafruit_dht.DHT22(board.D18)
 
 while True:
     try:
-        # show the values to the serial port
-        temperature = dhtDevice.temperature * (9 / 5) + 32
+        # Print the values to the serial port
+        temperature_c = dhtDevice.temperature
+        temperature_f = temperature_c * (9 / 5) + 32
         humidity = dhtDevice.humidity
-        print("Temp: {:.1f} F Humidity: {}% ".format(temperature, humidity))
+        print("Temp: {:.1f} F / {:.1f} C    Humidity: {}% "
+              .format(temperature_f, temperature_c, humidity))
 
     except RuntimeError as error:
-        print(error.args)
+        # Errors happen fairly often, DHT's are hard to read, just keep going
+        print(error.args[0])
 
     time.sleep(2.0)

examples/dht_to_led_display.py

@@ -35,6 +35,6 @@
         display.show()
 
     except RuntimeError as error:
-        print(error.args)
+        print(error.args[0])
 
     time.sleep(2.0)