diff --git a/cnc/sensors/ads111x.py b/cnc/sensors/ads111x.py
index 0831abe..f30db55 100644
--- a/cnc/sensors/ads111x.py
+++ b/cnc/sensors/ads111x.py
@@ -8,26 +8,36 @@ import threading
 ADS111x_ADDRESS = 0x48
 I2C_SLAVE = 0x0703
 
-# Initialize i2c interface and register it for closing on exit.
-__i2c_dev = os.open("/dev/i2c-1", os.O_SYNC | os.O_RDWR)
+
+class __I2CDev(object):
+    def __init__(self):
+        self._os_close = os.close
+        # Initialize i2c interface and register it for closing on exit.
+        self._dev = os.open("/dev/i2c-1", os.O_SYNC | os.O_RDWR)
+        if self._dev < 0:
+            raise ImportError("i2c device not found")
+        else:
+            if fcntl.ioctl(self._dev, I2C_SLAVE, ADS111x_ADDRESS) < 0:
+                self._close()
+                raise ImportError("Failed to set up i2c address")
+            else:
+                atexit.register(self._close)
+
+    def _close(self):
+        self._os_close(self._dev)
+
+    def write(self, data):
+        os.write(self._dev, data)
+
+    def read(self, n):
+        os.read(self._dev, n)
+
+i2c = __I2CDev()
 
 # mutex for multi threading requests
 lock = threading.Lock()
 
 
-def __close():
-    os.close(__i2c_dev)
-
-if __i2c_dev < 0:
-    raise ImportError("i2c device not found")
-else:
-    if fcntl.ioctl(__i2c_dev, I2C_SLAVE, ADS111x_ADDRESS) < 0:
-        __close()
-        raise ImportError("Failed to set up i2c address")
-    else:
-        atexit.register(__close)
-
-
 def measure(channel):
     """
     Measure voltage on chip input.
@@ -36,7 +46,7 @@ def measure(channel):
     :param channel: chip channel to use.
     :return: Voltage in Volts.
     """
-    global __i2c_dev
+    global i2c
     if channel < 0 or channel > 3:
         raise ValueError("Wrong channel")
     lock.acquire()
@@ -46,16 +56,16 @@ def measure(channel):
                        # single shot mode, +-4.096V, AINN = GND
                        ((0b100 | channel) << 12) | 0x8380
                        )
-    os.write(__i2c_dev, data)
+    i2c.write(data)
     # wait for conversion
     while True:
-        os.write(__i2c_dev, struct.pack("B", 0x01))
-        if struct.unpack(">H", os.read(__i2c_dev, 2))[0] & 0x8000 != 0:
+        i2c.write(data, struct.pack("B", 0x01))
+        if struct.unpack(">H", i2c.read(data, 2))[0] & 0x8000 != 0:
             break
         time.sleep(0.0001)
     # read result
-    os.write(__i2c_dev, struct.pack("B", 0x00))  # conversion register
-    v = struct.unpack(">h", os.read(__i2c_dev, 2))[0]
+    i2c.write(data, struct.pack("B", 0x00))  # conversion register
+    v = struct.unpack(">h", i2c.read(data, 2))[0]
     lock.release()
     return v / 8000.0  # / 32768.0 * 4.096 according to specified range