drivers: Add onewire driver and ds18x20 temperature sensor driver.

1 files changed, 104 insertions, 0 deletions

diff --git a/drivers/onewire/ds18x20.py b/drivers/onewire/ds18x20.py
new file mode 100644
index 000000000..06c9fc968
--- /dev/null
+++ b/drivers/onewire/ds18x20.py
@@ -0,0 +1,104 @@
+"""
+DS18x20 temperature sensor driver for MicroPython.
+
+This driver uses the OneWire driver to control DS18S20 and DS18B20
+temperature sensors.  It supports multiple devices on the same 1-wire bus.
+
+The following example assumes the ground of your DS18x20 is connected to
+Y11, vcc is connected to Y9 and the data pin is connected to Y10.
+
+>>> gnd = Pin('Y11')
+>>> gnd.init(Pin.OUT_PP)
+>>> gnd.low()
+        
+>>> vcc = Pin('Y9')
+>>> vcc.init(Pin.OUT_PP)
+>>> vcc.high()
+
+>>> d = DS18X20(Pin('Y10'))
+
+Call read_temps to read all sensors:
+
+>>> result = d.read_temps()
+>>> print(result)
+[20.875, 20.8125]
+
+Call read_temp to read the temperature of a specific sensor:
+
+>>> result = d.read_temp(d.roms[0])
+>>> print(result)
+20.25
+
+If only one DS18x20 is attached to the bus, then you don't need to 
+pass a ROM to read_temp:
+
+>>> result = d.read_temp()
+>>> print(result)
+20.25
+
+"""
+
+from onewire import OneWire
+
+class DS18X20(object):
+    def __init__(self, pin):
+        self.ow = OneWire(pin)
+        # Scan the 1-wire devices, but only keep those which have the
+        # correct # first byte in their rom for a DS18x20 device.
+        self.roms = [rom for rom in self.ow.scan() if rom[0] == 0x10 or rom[0] == 0x28]
+
+    def _select_rom(self, rom):
+        if rom:
+            self.ow.select_rom(rom)
+        else:
+            self.ow.skip_rom()
+
+    def read_temp(self, rom=None):
+        """
+        Read and return the temperature of one DS18x20 device.
+        Pass the 8-byte bytes object with the ROM of the specific device you want to read.
+        If only one DS18x20 device is attached to the bus you may omit the rom parameter.
+        """
+        ow = self.ow
+        ow.reset()
+        self._select_rom(rom)
+        ow.write_byte(0x44)  # Convert Temp
+        while True:
+            if ow.read_bit():
+                break
+        ow.reset()
+        self._select_rom(rom)
+        ow.write_byte(0xbe)  # Read scratch
+        data = ow.read_bytes(9)
+        return self.convert_temp(rom[0], data)
+
+    def read_temps(self):
+        """
+        Read and return the temperatures of all attached DS18x20 devices.
+        """
+        temps = []
+        for rom in self.roms:
+            temps.append(self.read_temp(rom))
+        return temps
+
+    def convert_temp(self, rom0, data):
+        """
+        Convert the raw temperature data into degrees celsius and return as a float.
+        """
+        temp_lsb = data[0]
+        temp_msb = data[1]
+        if rom0 == 0x10:
+            if temp_msb != 0:
+                # convert negative number
+                temp_read = temp_lsb >> 1 | 0x80  # truncate bit 0 by shifting, fill high bit with 1.
+                temp_read = -((~temp_read + 1) & 0xff) # now convert from two's complement
+            else:
+                temp_read = temp_lsb >> 1  # truncate bit 0 by shifting
+            count_remain = data[6]
+            count_per_c = data[7]
+            temp = temp_read - 0.25 + (count_per_c - count_remain) / count_per_c
+            return temp
+        elif rom0 == 0x28:
+            return (temp_msb << 8 | temp_lsb) / 16
+        else:
+            assert False