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Diff: WindVane.cpp
- Revision:
- 0:457832d52954
diff -r 000000000000 -r 457832d52954 WindVane.cpp --- /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; +}