dfrorp: Initial implementation

This module implements support for the DFRobot Analog ORP
(Oxidation/Reduction Potential) Meter.

It requires 5.0 volts, but the more accurate the voltage specified (to
the constructor), the more accurate the meter (paraphrased from the
wiki).

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

examples/c/CMakeLists.txt

@@ -93,6 +93,7 @@ add_example (bh1750)
 add_example (urm37)
 add_example (urm37-uart)
 add_example (hka5)
+add_example (dfrorp)
 
 # Custom examples
 add_custom_example (nmea_gps_i2c-example-c nmea_gps_i2c.c nmea_gps)

examples/c/dfrorp.c

@@ -0,0 +1,86 @@
+/*
+ * 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 <unistd.h>
+#include <signal.h>
+
+#include "dfrorp.h"
+
+bool shouldRun = true;
+
+void sig_handler(int signo)
+{
+  if (signo == SIGINT)
+    shouldRun = false;
+}
+
+int main()
+{
+  signal(SIGINT, sig_handler);
+
+//! [Interesting]
+
+  // Instantiate a DFRobot ORP sensor on analog pin A0 with an analog
+  // reference voltage of 5.0.
+  dfrorp_context sensor = dfrorp_init(0, 5.0);
+
+  if (!sensor)
+    {
+      printf("dfrorp_init() failed.\n");
+      return(1);
+    }
+
+  // To calibrate:
+  //
+  // Disconnect the sensor probe (but leave the sensor interface board
+  // connected).  Then run one of the examples while holding down the
+  // 'calibrate' button on the device.  Read the ORP value reported
+  // (it should be fairly small).
+  //
+  // This value is what you should supply to
+  // dfrorp_set_orp_cal_offset().  Then reconnect the probe to the
+  // interface board and you should be ready to go.
+  //
+  // DO NOT press the calibrate button on the interface board while
+  // the probe is attached or you can permanently damage the probe.
+  dfrorp_set_calibration_offset(sensor, 0.97);
+
+  // Every second, update and print values
+  while (shouldRun)
+    {
+      dfrorp_update(sensor);
+
+      printf("ORP = %f mV\n", dfrorp_get_orp(sensor));
+
+      sleep(1);
+    }
+
+//! [Interesting]
+
+  printf("Exiting...\n");
+
+  dfrorp_close(sensor);
+
+  return 0;
+}