add AHT40 sensor

sensors.py

@@ -22,6 +22,13 @@ except:
     print("Adafruit SHT4X not available!")
     enable_sht = False
 
+try:
+    import AHT20
+    enable_aht = True
+except:
+    print("Adafruit SHT4X not available!")
+    enable_aht = False
+
 # TODO client: add a way to disable live plotting? server: stop
 # sending data periodically to everybody!
 
@@ -114,6 +121,9 @@ if enable_sht:
     SHT40_DEFAULT = adafruit_sht4x.Mode.NOHEAT_HIGHPRECISION
     sht.mode = SHT40_DEFAULT
 
+if enable_aht:
+    aht = AHT20.AHT20()
+
 class SHT40(Sensor):
     def __init__(self, what, every=600):
         super().__init__()
@@ -160,6 +170,31 @@ class SHT40(Sensor):
         return self.store(
             time, temperature if self.measure == 'Temperature' else relative_humidity)
 
+class AHT40(Sensor):
+    def __init__(self, what):
+        super().__init__()
+        if what not in ("Temperature", "Humidity"):
+            print("ERROR: invalid sensor value: ", what)
+            return
+        self.measure = what
+        if not enable_aht:
+            return
+
+    def is_temperature(self):
+        return self.measure == "Temperature"
+
+    def is_humidity(self):
+        return self.measure == "Humidity"
+
+    def read(self):
+        time = perf_counter()
+        if not enable_aht:
+            return (time, None)
+        return self.store(
+            time, aht20.get_temperature_crc8() if (
+                self.measure == 'Temperature'
+            ) else aht20.get_humidity_crc8())
+
 class Sensors():
     def __init__(self, history=2621440):
         self.starttime = (datetime.now(), perf_counter())
@@ -181,6 +216,8 @@ class Sensors():
             'T_food':     Temperature1W('28-06214252b671'),
             'T_ext':      SHT40('Temperature'),
             'H_ext':      SHT40('Humidity'),
+            'T_ext2':     AHT40('Temperature'),
+            'H_ext2':     AHT40('Humidity'),
             'heater':     GPIOState(22),
             'humidifier/heater2': GPIOState(17),
             'freezer':    GPIOState(14),