teams: Initial implementation

The driver adds support for the Veris TEAMS Temperature Transmitter.

It provides it's output via a 4-20ma current loop.  The supported
temperature range is 10C to 35C.

This sensor was developed with a Cooking Hacks (Libelium)
4-channel 4-20ma Arduino interface shield.  For this interface,
the receiver resistance (rResistor) was specified as 165.0
ohms.

Signed-off-by: Jon Trulson <jtrulson@ics.com>
Signed-off-by: Abhishek Malik <abhishek.malik@intel.com>

src/teams/teams.cxx

@@ -0,0 +1,125 @@
+/*
+ * 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 "teams.h"
+
+using namespace upm;
+using namespace std;
+
+// for current loop reads that seems a little noisy, we average over
+// several aio reads.
+static const int maxSamples = 50;
+
+// conversion from celcius to fahrenheit
+
+static float c2f(float c)
+{
+  return (c * (9.0 / 5.0) + 32.0);
+}
+
+
+TEAMS::TEAMS(int tPin, float rResistor, float aref) :
+  m_aioTemp(tPin)
+{
+  if (rResistor < 0.0)
+    {
+      throw std::out_of_range(std::string(__FUNCTION__) +
+                              ": rResistor must be >= 0.0");
+    }
+
+  m_aResTemp = (1 << m_aioTemp.getBit());
+
+  m_temperature = 0.0;
+
+  m_aref = aref;
+  m_rResistor = rResistor;
+  m_connected = false;
+
+  // this will only be non-zero when using a direct 4-20ma interface
+  // like libelium
+  m_rawMilliamps = 0.0;
+
+  m_offset = 0.0;
+}
+
+TEAMS::~TEAMS()
+{
+}
+
+void TEAMS::update()
+{
+  float milliamps = 0.0;
+
+  int val = average(maxSamples);
+  float volts = (float(val) * (m_aref / m_aResTemp));
+
+  // valid temp range is 25.0 (35C - 10C), current loop range is 16ma
+  // (20ma - 4ma)
+  if (m_rResistor)
+    {
+      // direct 4-20 current loop interface
+      milliamps = (volts / m_rResistor * 1000.0) + m_offset;
+      m_rawMilliamps = milliamps;
+
+      // subtract 0 (4ma) value
+      milliamps -= 4.0;
+      if (milliamps < 0.0) // not connected
+        {
+          milliamps = 0.0;
+          m_connected = false;
+        }
+      else
+        m_connected = true;
+
+      m_temperature = (milliamps * (25.0 / 16.0)) + 10.0;
+    }
+  else
+    {
+      // normal analog read, already scaled to 0-5v, always connected
+      m_temperature = ((volts / m_aref) * 25.0) + 10.0;
+      m_connected = true;
+    }
+}
+
+float TEAMS::getTemperature(bool fahrenheit)
+{
+  if (fahrenheit)
+    return c2f(m_temperature);
+  else
+    return m_temperature;
+}
+
+int TEAMS::average(int samples)
+{
+  if (samples <= 0)
+    samples = 1;
+
+  int avg = 0;
+  for (int i=0; i<samples; i++)
+    avg += m_aioTemp.read();
+
+  return (avg / samples);
+}