Add support for Sharp 2Y0A21 sensor

Author: virtuald

robotpy_ext/common_drivers/distance_sensors.py

@@ -36,6 +36,40 @@ def getDistance(self):
         return max(min(d, 145.0), 22.5)
 
 
+class SharpIR2Y0A21:
+    """
+        Sharp GP2Y0A21YK0F is an analog IR sensor capable of measuring
+        distances from 10cm to 80cm. Output distance is measured in
+        centimeters.
+        
+        Distance is calculated using the following equation derived from
+        the graph provided in the datasheet::
+        
+            26.449*x ^ -1.226
+            
+        .. warning:: FRC Teams: the case on these sensors is conductive and
+                     grounded, and should not be mounted on a metallic
+                     surface!
+    """
+
+    def __init__(self, port):
+        """:param port: Analog port number"""
+        self.distance = wpilib.AnalogInput(port)
+
+    def getDistance(self):
+        """
+            :returns: distance in centimeters. The output is constrained to
+                      be between 10 and 80
+        """
+
+        # Don't allow zero/negative values
+        v = max(self.distance.getVoltage(), 0.00001)
+        d = 26.449 * math.pow(v, -1.226)
+
+        # Constrain output
+        return max(min(d, 80.0), 10.0)
+
+
 class SharpIRGP2Y0A41SK0F:
     """
         Sharp GP2Y0A41SK0F is an analog IR sensor capable of measuring