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jerryneedelljerryneedell
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create private functions for pulseio and bitbang version of getting pulses
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‎adafruit_dht.py

+61-54
Original file line numberDiff line numberDiff line change
@@ -91,7 +91,7 @@ def _pulses_to_binary(self, pulses, start, stop):
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return binary
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94-
def _get_pulses(self):
94+
def _get_pulses_pulseio(self):
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""" _get_pulses implements the communication protcol for
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DHT11 and DHT22 type devices. It sends a start signal
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of a specific length and listens and measures the
@@ -102,54 +102,61 @@ def _get_pulses(self):
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pulses will have 81 elements for the DHT11/22 type devices.
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"""
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pulses = array.array('H')
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# create the PulseIn object using context manager
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with pulseio.PulseIn(self._pin, 81, True) as pulse_in:
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# The DHT type device use a specialize 1-wire protocol
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# The microprocessor first sends a LOW signal for a
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# specific length of time. Then the device sends back a
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# series HIGH and LOW signals. The length the HIGH signals
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# represents the device values.
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pulse_in.pause()
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pulse_in.clear()
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pulse_in.resume(self._trig_wait)
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# loop until we get the return pulse we need or
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# time out after 1/4 second
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tmono = time.monotonic()
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while time.monotonic() - tmono < 0.25:
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pass # time out after 1/4 seconds
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pulse_in.pause()
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while pulse_in:
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pulses.append(pulse_in.popleft())
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pulse_in.resume()
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return pulses
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126+
def _get_pulses_bitbang(self):
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""" _get_pulses implements the communication protcol for
128+
DHT11 and DHT22 type devices. It sends a start signal
129+
of a specific length and listens and measures the
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return signal lengths.
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106-
if _USE_PULSEIO:
107-
# create the PulseIn object using context manager
108-
with pulseio.PulseIn(self._pin, 81, True) as pulse_in:
109-
110-
# The DHT type device use a specialize 1-wire protocol
111-
# The microprocessor first sends a LOW signal for a
112-
# specific length of time. Then the device sends back a
113-
# series HIGH and LOW signals. The length the HIGH signals
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# represents the device values.
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pulse_in.pause()
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pulse_in.clear()
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pulse_in.resume(self._trig_wait)
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# loop until we get the return pulse we need or
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# time out after 1/4 second
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tmono = time.monotonic()
122-
while time.monotonic() - tmono < 0.25:
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pass # time out after 1/4 seconds
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pulse_in.pause()
125-
while pulse_in:
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pulses.append(pulse_in.popleft())
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pulse_in.resume()
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else:
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with DigitalInOut(self._pin) as dhtpin:
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# we will bitbang if no pulsein capability
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transitions = []
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# Signal by setting pin high, then low, and releasing
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dhtpin.direction = Direction.OUTPUT
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dhtpin.value = True
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time.sleep(0.1)
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dhtpin.value = False
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time.sleep(0.001)
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timestamp = time.monotonic() # take timestamp
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dhtval = True # start with dht pin true because its pulled up
141-
dhtpin.direction = Direction.INPUT
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dhtpin.pull = Pull.UP
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while time.monotonic() - timestamp < 0.25:
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if dhtval != dhtpin.value:
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dhtval = not dhtval # we toggled
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transitions.append(time.monotonic()) # save the timestamp
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# convert transtions to microsecond delta pulses:
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# use last 81 pulses
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transition_start = max(1, len(transitions) - 81)
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for i in range(transition_start, len(transitions)):
151-
pulses_micro_sec = int(1000000 * (transitions[i] - transitions[i-1]))
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pulses.append(min(pulses_micro_sec, 65535))
132+
return pulses (array.array uint16) contains alternating high and low
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transition times starting with a low transition time. Normally
134+
pulses will have 81 elements for the DHT11/22 type devices.
135+
"""
136+
pulses = array.array('H')
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with DigitalInOut(self._pin) as dhtpin:
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# we will bitbang if no pulsein capability
139+
transitions = []
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# Signal by setting pin high, then low, and releasing
141+
dhtpin.direction = Direction.OUTPUT
142+
dhtpin.value = True
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time.sleep(0.1)
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dhtpin.value = False
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time.sleep(0.001)
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timestamp = time.monotonic() # take timestamp
147+
dhtval = True # start with dht pin true because its pulled up
148+
dhtpin.direction = Direction.INPUT
149+
dhtpin.pull = Pull.UP
150+
while time.monotonic() - timestamp < 0.25:
151+
if dhtval != dhtpin.value:
152+
dhtval = not dhtval # we toggled
153+
transitions.append(time.monotonic()) # save the timestamp
154+
# convert transtions to microsecond delta pulses:
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# use last 81 pulses
156+
transition_start = max(1, len(transitions) - 81)
157+
for i in range(transition_start, len(transitions)):
158+
pulses_micro_sec = int(1000000 * (transitions[i] - transitions[i-1]))
159+
pulses.append(min(pulses_micro_sec, 65535))
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return pulses
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def measure(self):
@@ -168,7 +175,10 @@ def measure(self):
168175
(time.monotonic()-self._last_called) > delay_between_readings):
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self._last_called = time.monotonic()
170177

171-
pulses = self._get_pulses()
178+
if _USE_PULSEIO:
179+
pulses = self._get_pulses_pulseio()
180+
else:
181+
pulses = self._get_pulses_bitbang()
172182
#print(len(pulses), "pulses:", [x for x in pulses])
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174184
if len(pulses) >= 80:
@@ -179,14 +189,11 @@ def measure(self):
179189
if self._dht11:
180190
# humidity is 1 byte
181191
self._humidity = buf[0]
182-
else:
183-
# humidity is 2 bytes
184-
self._humidity = ((buf[0]<<8) | buf[1]) / 10
185-
186-
if self._dht11:
187192
# temperature is 1 byte
188193
self._temperature = buf[2]
189194
else:
195+
# humidity is 2 bytes
196+
self._humidity = ((buf[0]<<8) | buf[1]) / 10
190197
# temperature is 2 bytes
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# MSB is sign, bits 0-14 are magnitude)
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raw_temperature = (((buf[2] & 0x7f)<<8) | buf[3]) / 10

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