Add asynchhronous functions

adafruit_ds18x20.py

@@ -40,6 +40,8 @@
 _WR_SCRATCH = b'\x4E'
 _CONVERSION_TIMEOUT = const(1)
 RESOLUTION = (9, 10, 11, 12)
+# Maximum conversion delay in seconds, from DS18B20 datasheet.
+_CONVERSION_DELAY = {9:0.09375, 10:0.1875, 11:0.375, 12:0.750}
 
 class DS18X20(object):
     """Class which provides interface to DS18X20 temperature sensor."""
@@ -49,6 +51,7 @@ def __init__(self, bus, address):
             self._address = address
             self._device = OneWireDevice(bus, address)
             self._buf = bytearray(9)
+            self._conv_delay = _CONVERSION_DELAY[12]  # pessimistic default
         else:
             raise ValueError('Incorrect family code in device address.')
 
@@ -111,3 +114,15 @@ def _write_scratch(self, buf):
         with self._device as dev:
             dev.write(_WR_SCRATCH)
             dev.write(buf, end=3)
+
+    def start_temperature_read(self):
+        """Start asynchronous conversion, returns immediately.
+        Returns maximum conversion delay [seconds] based on resolution."""
+        with self._device as dev:
+            dev.write(_CONVERT)
+        return _CONVERSION_DELAY[self.resolution]
+
+    def read_temperature(self):
+        """Read the temperature. No polling of the conversion busy bit
+        (assumes that the conversion has completed)."""
+        return self._read_temp()

docs/examples.rst

@@ -1,8 +1,12 @@
 Simple test
 ------------
 
-Ensure your device works with this simple test.
+Ensure your device works with these simple tests.
 
 .. literalinclude:: ../examples/ds18x20_simpletest.py
     :caption: examples/ds18x20_simpletest.py
     :linenos:
+
+.. literalinclude:: ../examples/ds18x20_asynctest.py
+    :caption: examples/ds18x20_asynctest.py
+    :linenos:

examples/ds18x20_asynctest.py

@@ -0,0 +1,31 @@
+# Simple demo of printing the temperature from the first found DS18x20 sensor every second.
+# Using the asynchronous functions start_temperature_read() and
+# read_temperature() to allow the main loop to keep processing while
+# the conversion is in progress.
+# Author: Louis Bertrand, based on original by Tony DiCola
+
+import time
+
+import board
+
+from adafruit_onewire.bus import OneWireBus
+from adafruit_ds18x20 import DS18X20
+
+
+# Initialize one-wire bus on board pin D1.
+ow_bus = OneWireBus(board.D1)
+
+# Scan for sensors and grab the first one found.
+ds18 = DS18X20(ow_bus, ow_bus.scan()[0])
+ds18.resolution = 12
+
+# Main loop to print the temperature every second.
+while True:
+    conversion_delay = ds18.start_temperature_read()
+    conversion_ready_at = time.monotonic() + conversion_delay
+    print("waiting", end="")
+    while time.monotonic() < conversion_ready_at:
+        print(".", end="")
+        time.sleep(0.1)
+    print('\nTemperature: {0:0.3f}C\n'.format(ds18.read_temperature()))
+    time.sleep(1.0)