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>

src/dfrorp/dfrorp.h

@@ -0,0 +1,181 @@
+/*
+ * 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.
+ */
+
+#pragma once
+
+#include <stdint.h>
+#include "upm.h"
+#include "mraa/aio.h"
+#include "mraa/gpio.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+  /**
+   * @brief UPM C API for the DFRobot ORP (Oxidation/Reduction
+   * Potential) Sensor
+   *
+   * The driver was tested with the DFRobot ORP Analog Sensor.
+   *
+   * 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.
+   *
+   * @snippet dfrorp.c Interesting
+   */
+
+  /**
+   * Device context
+   */
+  typedef struct _dfrorp_context {
+    mraa_aio_context    aio;
+
+    // analog ADC resolution
+    float               a_res;
+
+    // analog reference voltage
+    float               a_ref;
+
+    // for external offset and scaling of the results
+    float               offset;
+    float               scale;
+
+    // For sensor interface board calibration
+    float               orp_cal_offset;
+
+    // our measurements
+
+    // ORP measurement (mV)
+    float               orp;
+
+    // volts
+    float               volts;
+
+    // normalized ADC
+    float               normalized;
+  } *dfrorp_context;
+
+  /**
+   * DFRORP Initializer
+   *
+   * @param apin Analog pin to use.
+   * @param a_ref The analog reference voltage in use
+   */
+  dfrorp_context dfrorp_init(unsigned int apin, float a_ref);
+
+  /**
+   * DFRORP sensor close function
+   */
+  void dfrorp_close(dfrorp_context dev);
+
+  /**
+   * Read the sensor status and update internal state.  dfrorp_update()
+   * must have been called before calling dfrorp_get_orp(),
+   * dfrorp_get_normalized(), or dfrorp_get_volts().
+   *
+   * @param dev sensor context
+   * @return UPM result
+   */
+  upm_result_t dfrorp_update(const dfrorp_context dev);
+
+  /**
+   * Set sensor offset.  This offset is applied to the ORP value
+   * before scaling.  Default is 0.0.
+   *
+   * @param dev sensor context pointer
+   * @param offset Offset to apply to the computed ORP value
+   */
+  void dfrorp_set_offset(const dfrorp_context dev, float offset);
+
+  /**
+   * Set sensor scale.  The ORP return value is scaled by this value
+   * before the offset is applied.  Default is 1.0.
+   *
+   * @param dev sensor context pointer
+   * @param scale The scale to apply to the computed ORP value
+   */
+  void dfrorp_set_scale(const dfrorp_context dev, float scale);
+
+  /**
+   * Get computed ORP (in millivolts) value from the
+   * sensor. dfrorp_update() must have been called prior to calling
+   * this function.
+   *
+   * @param dev sensor context pointer
+   * @return ORP value in millivolts
+   */
+  float dfrorp_get_orp(const dfrorp_context dev);
+
+  /**
+   * Set the calibration offset for the device.  This is
+   * determined by disconnecting the sensor probe (but leaving 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.
+   *
+   * This (low) ORP value is what you should supply to this function.
+   * 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.
+   *
+   * @param dev sensor context pointer
+   * @param offset The ORP offset obtained during calibration.
+   */
+  void dfrorp_set_calibration_offset(const dfrorp_context dev, float offset);
+
+  /**
+   * Get the raw measured volts from the sensor. dfrorp_update() must
+   * have been called prior to calling this function.
+   *
+   * @param dev sensor context pointer
+   * @return voltage read from the sensor
+   */
+  float dfrorp_get_volts(const dfrorp_context dev);
+
+  /**
+   * Get the raw normalized ADC values from the sensor.
+   * dfrorp_update() must have been called prior to calling this
+   * function.
+   *
+   * @param dev sensor context pointer
+   * @return normalized ADC value read from the sensor
+   */
+  float dfrorp_get_normalized(const dfrorp_context dev);
+
+#ifdef __cplusplus
+}
+#endif