Diff: WindVane.cpp

Revision:

0:457832d52954

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/WindVane.cpp	Sat Feb 25 03:23:51 2012 +0000
@@ -0,0 +1,96 @@
+/* Copyright 2012 Adam Green (http://mbed.org/users/AdamGreen/)
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+/* Declaration of class to interface with wind vane sensor Sparkfun Weather Meters: 
+    http://www.sparkfun.com/products/8942
+*/
+#include <mbed.h>
+#include "WindVane.h"
+
+
+#define REV_PER_SECOND_TO_KMPH  2.4f
+#define PARALLEL_R(R1, R2) (((R1) * (R2)) / ((R1) + (R2)))
+#define ARRAY_SIZE(X) (sizeof(X)/sizeof(X[0]))
+
+struct SDescription
+{
+    const char* DirectionString;
+    float       DirectionAngle;
+    float       SensorResistance;
+};
+
+
+static SDescription g_WindVaneDescriptionTable[16] = {
+    { "North",            0.0f,  33.0f * 1000.0f },
+    { "North North East", 22.5f, PARALLEL_R(33.0f * 1000.0f, 8.2f * 1000.0f) },
+    { "North East",       45.0f, 8.2f * 1000.0f },
+    { "East North East",  67.5f, PARALLEL_R(8.2f * 1000.0f, 1000.0f) },
+    { "East",             90.0f, 1000.0f },
+    { "East South East",  112.5f, PARALLEL_R(1000.0f, 2.2f * 1000.0f) },
+    { "South East",       135.0f, 2.2f * 1000.0f },
+    { "South South East", 157.5f, PARALLEL_R(2.2f * 1000.0f, 3.9f * 1000.0f) },
+    { "South",            180.0f, 3.9f * 1000.0f },
+    { "South South West", 202.5f, PARALLEL_R(3.9f * 1000.0f, 16.0f * 1000.0f) },
+    { "South West",       225.0f, 16.0f * 1000.0f },
+    { "West South West",  247.5f, PARALLEL_R(16.0f * 1000.0f, 120.0f * 1000.0f) },
+    { "West",             270.0f, 120.0f * 1000.0f },
+    { "West North West",  292.5f, PARALLEL_R(120.0f * 1000.0f, 64.9f * 1000.0f) },
+    { "North West",       315.0f, 64.9f * 1000.0f },
+    { "North North West", 337.5f, PARALLEL_R(64.9f * 1000.0f, 33.0f * 1000.0f) }
+};
+
+
+CWindVane::CWindVane(PinName WindVanePin, float WindVaneSeriesResistance)
+    : m_WindVaneAnalogIn(WindVanePin)
+{
+    for (size_t i = 0 ; i < ARRAY_SIZE(g_WindVaneDescriptionTable) ; i++)
+    {
+        SDescription* pDescription = &g_WindVaneDescriptionTable[i];
+
+        m_WindVaneVoltageTable[i] = pDescription->SensorResistance /
+                                    (pDescription->SensorResistance + WindVaneSeriesResistance);
+    }
+}
+
+const char* CWindVane::GetWindDirectionAsString()
+{
+    return g_WindVaneDescriptionTable[DetermineWindDirectionIndex()].DirectionString;
+}
+
+float CWindVane::GetWindDirectionAsAngle()
+{
+    return g_WindVaneDescriptionTable[DetermineWindDirectionIndex()].DirectionAngle;
+}
+
+size_t CWindVane::DetermineWindDirectionIndex()
+{
+    float WindVaneSensorVoltage = m_WindVaneAnalogIn.read();
+
+    // Default to the first entry being closest.
+    size_t ClosestIndex = 0;
+    float  ClosestDelta = fabs(m_WindVaneVoltageTable[0] - WindVaneSensorVoltage);
+    
+    // Walk the rest of the entries to see if there is another which is closer.
+    for (size_t i = 1 ; i < ARRAY_SIZE(m_WindVaneVoltageTable) ; i++)
+    {
+        float Delta = fabs(m_WindVaneVoltageTable[i] - WindVaneSensorVoltage);
+        if (Delta < ClosestDelta)
+        {
+            ClosestDelta = Delta;
+            ClosestIndex = i;
+        }
+    }
+    
+    return ClosestIndex;
+}