temphum: support multiple temp/relhum sensors

4 files changed, 78 insertions, 0 deletions

diff --git a/src/home/temphum/__init__.py b/src/home/temphum/__init__.py
new file mode 100644
index 0000000..55a7e1f
--- /dev/null
+++ b/src/home/temphum/__init__.py
@@ -0,0 +1,18 @@
+from .base import SensorType, TempHumSensor
+from .si7021 import Si7021
+from .dht12 import DHT12
+
+__all__ = [
+    'SensorType',
+    'TempHumSensor',
+    'create_sensor'
+]
+
+
+def create_sensor(type: SensorType, bus: int) -> TempHumSensor:
+    if type == SensorType.Si7021:
+        return Si7021(bus)
+    elif type == SensorType.DHT12:
+        return DHT12(bus)
+    else:
+        raise ValueError('unexpected sensor type')
diff --git a/src/home/temphum/base.py b/src/home/temphum/base.py
new file mode 100644
index 0000000..e774433
--- /dev/null
+++ b/src/home/temphum/base.py
@@ -0,0 +1,25 @@
+import smbus
+
+from abc import abstractmethod, ABC
+from enum import Enum
+
+
+class TempHumSensor:
+    @abstractmethod
+    def humidity(self) -> float:
+        pass
+
+    @abstractmethod
+    def temperature(self) -> float:
+        pass
+
+
+class I2CTempHumSensor(TempHumSensor, ABC):
+    def __init__(self, bus: int):
+        super().__init__()
+        self.bus = smbus.SMBus(bus)
+
+
+class SensorType(Enum):
+    Si7021 = 'si7021'
+    DHT12 = 'dht12'
diff --git a/src/home/temphum/dht12.py b/src/home/temphum/dht12.py
new file mode 100644
index 0000000..d495766
--- /dev/null
+++ b/src/home/temphum/dht12.py
@@ -0,0 +1,22 @@
+from .base import I2CTempHumSensor
+
+
+class DHT12(I2CTempHumSensor):
+    i2c_addr = 0x5C
+        
+    def _measure(self):
+        raw = self.bus.read_i2c_block_data(self.i2c_addr, 0, 5)
+        if (raw[0] + raw[1] + raw[2] + raw[3]) & 0xff != raw[4]:
+            raise ValueError("checksum error")
+        return raw
+
+    def temperature(self) -> float:
+        raw = self._measure()
+        temp = raw[2] + (raw[3] & 0x7f) * 0.1
+        if raw[3] & 0x80:
+            temp *= -1
+        return temp
+
+    def humidity(self) -> float:
+        raw = self._measure()
+        return raw[0] + raw[1] * 0.1
diff --git a/src/home/temphum/si7021.py b/src/home/temphum/si7021.py
new file mode 100644
index 0000000..6289e15
--- /dev/null
+++ b/src/home/temphum/si7021.py
@@ -0,0 +1,13 @@
+from .base import I2CTempHumSensor
+
+
+class Si7021(I2CTempHumSensor):
+    i2c_addr = 0x40
+
+    def temperature(self) -> float:
+        raw = self.bus.read_i2c_block_data(self.i2c_addr, 0xE3, 2)
+        return 175.72 * (raw[0] << 8 | raw[1]) / 65536.0 - 46.85
+
+    def humidity(self) -> float:
+        raw = self.bus.read_i2c_block_data(self.i2c_addr, 0xE5, 2)
+        return 125.0 * (raw[0] << 8 | raw[1]) / 65536.0 - 6.0