dfrec: Initial implementation

This module implements support for the DFRobot EC (Electrical
Conductivity) meter.  It relies on the use of the DS18B20 UPM C module
for temperature gathering.

It has a pretty complicated calibration procedure which is somewhat
documented on the DFRobot wiki.  Functions have been added to support
changing the various coefficients as desired.

Signed-off-by: Jon Trulson <jtrulson@ics.com>

examples/java/DFREC_Example.java

@@ -0,0 +1,59 @@
+/*
+ * 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.
+ */
+
+import upm_dfrec.DFREC;
+
+public class DFREC_Example
+{
+    public static void main(String[] args) throws InterruptedException
+    {
+// ! [Interesting]
+
+        // Instantiate a DFRobot EC sensor on analog pin A0, with a ds18b20
+        // temperature sensor connected to UART 0, and a device index (for
+        // the ds1820b uart bus) of 0, and an analog reference voltage of
+        // 5.0.
+        DFREC sensor = new DFREC(0, 0, 0, 5.0f);
+
+        // Every 2 seconds, update and print values
+        while (true)
+            {
+                sensor.update();
+
+                System.out.println("EC = "
+                                   + sensor.getEC()
+                                   + " ms/cm");
+                System.out.println("Volts = "
+                                   + sensor.getVolts()
+                                   + ", Temperature = "
+                                   + sensor.getTemperature()
+                                   + " C");
+
+                System.out.println();
+                Thread.sleep(2000);
+            }
+
+// ! [Interesting]
+    }
+}