hx711: Initial implementation HX711 24bit ADC module

Signed-off-by: Rafael Neri <rafael.neri@gmail.com>
Signed-off-by: Mihai Tudor Panu <mihai.tudor.panu@intel.com>

src/hx711/hx711.h

@@ -0,0 +1,135 @@
+/*
+*
+* Author: Rafael da Mata Neri <rafael.neri@gmail.com>
+* Copyright (c) 2015 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 <unistd.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <string.h>
+#include <mraa/gpio.h>
+
+namespace upm {
+
+     /**
+      * @brief HX711 24bit ADC library
+      * @defgroup hx711 libupm-hx711
+      */
+
+     /**
+      * @brief C++ API for HX711
+      *
+      * [HX711](http://www.dfrobot.com/image/data/SEN0160/hx711_english.pdf) is 
+      * a precision 24-bit analog- to-digital converter (ADC) designed for weigh
+      * scales and industrial control applications to interface directly with a 
+      * bridge sensor. This module was tested on the Intel Galileo Gen2.
+      *
+      * @ingroup hx711 hx711
+      * @snippet hx711.cxx Interesting
+      * @image html hx711.jpeg
+      */
+      class HX711 {
+      public:
+            /**
+            * HX711 module constructor
+            *
+            * @param data define the data pin
+            * @param sck define the clock pin
+            * @param gain define the gain factor
+            * Valid values are 128 or 64 for channel A; channel B works with 32 gain factor only
+            */
+            HX711(uint8_t data, uint8_t sck, uint8_t gain = 128);
+
+            /**
+            * HX711 module Destructor
+            */
+            ~HX711();
+
+
+            /**
+            * Waits for the chip to be ready and returns a reading
+            *
+            * @return raw adc read
+            */
+            unsigned long read();
+
+            /**
+            * Set the gain factor; takes effect only after a call to read()
+            * channel A can be set for a 128 or 64 gain; channel B has a fixed 32 gain
+            * depending on the parameter, the channel is also set to either A or B
+            * @param gain define the gain factor
+            */
+            void setGain(uint8_t gain = 128);
+
+            /**
+            * Returns an average reading
+            * @param times define how many times to read
+            * @return the avarage reading
+            */
+            unsigned long readAverage(uint8_t times = 10);
+
+            /**
+            * Returns (readAverage() - OFFSET)
+            * @param times define how many readings to do
+            * @return the current value without the tare weight
+            */
+            double getValue(uint8_t times = 10);
+
+            /**
+            * Returns getValue() divided by SCALE
+            * @param times define how many readings to do
+            * @return the raw value divided by a value obtained via calibration
+            */
+            float getUnits(uint8_t times = 1);
+
+            /**
+            * Set the OFFSET value for tare weight
+            * @param times define how many times to read the tare value
+            */
+            void tare(uint8_t times = 10);
+
+            /**
+            * Set the SCALE value 
+            * This value is used to convert the raw data to "human readable" data (measure units)
+            * @param scale value obtained via calibration
+            */
+            void setScale(float scale = 1.f);
+       private:
+            mraa_gpio_context m_sckPinCtx; // Power Down and Serial Clock Input Pin
+            mraa_gpio_context m_dataPinCtx; // Serial Data Output Pin
+            
+            uint8_t GAIN; // amplification factor
+            unsigned long OFFSET; // used for tare weight
+            float SCALE; // used to return weight in grams, kg, ounces, whatever
+
+            
+            /**
+            * Set the OFFSET value 
+            * The value that's subtracted from the actual reading (tare weight)
+            * @param scale value obtained via calibration
+            */
+            void setOffset(long offset = 0);
+     };
+
+}