hdxxvxta: Initial implementation

This driver was developed using the Veris HD2NVSTA1 humidity
transmitter.  The 'T' variant supports a temperature transmitter as
well.  Both signals are provided by the device as analog 0-5Vdc or
0-10Vdc outputs.

The A1 variant supports a temperature range of -40C-50C, while the A2
variant supports a range of 0C-50C.  Humidity ranges for all devices
in this device family range from 0% to 100% (non-condensing).

Temperature measurement can be disabled by passing -1 as the
temperature analog pin to the constructor.

Signed-off-by: Jon Trulson <jtrulson@ics.com>
Signed-off-by: Mihai Tudor Panu <mihai.tudor.panu@intel.com>

src/hdxxvxta/hdxxvxta.cxx

@@ -0,0 +1,122 @@
+/*
+ * Author: Jon Trulson <jtrulson@ics.com>
+ * Copyright (c) 2016 Intel Corporation.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+ * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+ * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+#include <iostream>
+
+#include "hdxxvxta.h"
+
+using namespace upm;
+using namespace std;
+
+// conversion from celcius to fahrenheit
+
+static float c2f(float c)
+{
+  return (c * (9.0 / 5.0) + 32.0);
+}
+
+
+HDXXVXTA::HDXXVXTA(int hPin, int tPin, float aref) :
+  m_aioHum(hPin), m_aioTemp(0)
+{
+  if (tPin >= 0)
+    m_hasTemp = true;
+  else
+    m_hasTemp = false;
+
+  m_temperature = 0.0;
+  m_humidity = 0.0;
+
+  if (m_hasTemp)
+    {
+      m_aioTemp = new mraa::Aio(tPin);
+      m_aResTemp = (1 << m_aioTemp->getBit());
+    }
+  else
+    m_aResTemp = 0;
+
+  m_aResHum = (1 << m_aioHum.getBit());
+  m_aref = aref;
+
+  // set the default temperature range to the A1 series (-40C-50C),
+  // regardless of whether temperature measuring is enabled
+  setRange(RANGE_MINUS40_50);
+}
+
+HDXXVXTA::~HDXXVXTA()
+{
+  if (m_aioTemp)
+    delete m_aioTemp;
+}
+
+void HDXXVXTA::update()
+{
+  // temperature
+  int val;
+  float volts;
+
+  if (m_hasTemp)
+    {
+      val = m_aioTemp->read();
+      volts = (float(val) * (m_aref / m_aResTemp));
+
+      switch (m_range)
+        {
+        case RANGE_MINUS40_50:
+          // valid range is 50 + abs(-40) = 90
+          m_temperature = ((volts / m_aref) * 90.0) - 40.0;
+          break;
+          
+        case RANGE_0_50:
+          // valid range is 50
+          m_temperature = ((volts / m_aref) * 50.0);
+          break;
+          
+        default:
+          // shouldn't happen, but...
+          throw std::out_of_range(std::string(__FUNCTION__) +
+                                  ": internal error, invalid range value");
+          break;
+        }
+    }
+
+  // humidity
+  val = m_aioHum.read();
+  volts = (float(val) * (m_aref / m_aResHum));
+  m_humidity = ((volts / m_aref) * 100.0);
+}
+
+float HDXXVXTA::getTemperature(bool fahrenheit)
+{
+  if (fahrenheit)
+    return c2f(m_temperature);
+  else
+    return m_temperature;
+}
+
+float HDXXVXTA::getHumidity()
+{
+  return m_humidity;
+}
+