HX711.h

00001 /*
00002  * Copyright (c) 2020 Zoltan Hudak <hudakz@outlook.com>
00003  * All rights reserved.
00004  *
00005  * This program is free software: you can redistribute it and/or modify
00006  * it under the terms of the GNU General Public License as published by
00007  * the Free Software Foundation, either version 3 of the License, or
00008  * (at your option) any later version.
00009  *
00010  * This program is distributed in the hope that it will be useful,
00011  * but WITHOUT ANY WARRANTY; without even the implied warranty of
00012  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
00013  * GNU General Public License for more details.
00014  *
00015  * You should have received a copy of the GNU General Public License
00016  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
00017  */
00018 
00019 #ifndef _HX711_H_
00020 #define _HX711_H_
00021 #include "mbed.h"
00022 
00023 /**
00024  * Class for communication with the HX711 24-Bit Analog-to-Digital converter (ADC)
00025  * (Developed for Weigh Scales by AVIA Semiconductor.)
00026  * This library is based on the library at https://github.com/bogde/HX711
00027  */
00028 class   HX711
00029 {
00030 public:
00031     /**
00032      * Creates an HX711 object
00033      * @param avdd Analog power supply voltage [V]
00034      * @param sck PinName of the clock pin (digital output)
00035      * @param dout PinName of the data pin (digital input)
00036      * @param drift Chip's input offset drift [V]
00037      * @param gain Channel selection is made by passing the associated gain:
00038      *      128 or 64 for channel A, 32 for channel B
00039      */
00040     HX711(float avdd, PinName sck, PinName dout, uint8_t gain, float drift = 0) :
00041     _avdd(avdd),
00042     _sck(sck),
00043     _dout(dout, PullUp),
00044     _drift(drift)
00045     {
00046         setGain(gain);
00047     }
00048 
00049     /**
00050      * Check if the sensor is ready.
00051      * From the datasheet: When output data is not ready for retrieval,
00052      * digital output pin _dout is high. Serial clock input _sck should be low.
00053      * When _dout goes low, it indicates data is ready for retrieval.
00054      * @return true if _dout.read() == 0
00055      */
00056     bool isReady() { return _dout.read() == 0; }
00057 
00058     /**
00059      * Returns a raw int reading
00060      * @return int sensor output value
00061      */
00062     uint32_t readInt();
00063 
00064     /**
00065      * Obtains input voltage in mV biased by chip's input offset drift
00066      * @return float
00067      */
00068     float read();
00069 
00070     /**
00071      * Puts the chip into power down mode
00072      */
00073     void powerDown() { _sck.write(0); _sck.write(1); }
00074 
00075     /**
00076      * Wakes up the chip after power down mode
00077      */
00078     void powerUp() { _sck.write(0); }
00079 
00080     /**
00081      * Set the gain factor; takes effect only after a call to read()
00082      * channel A can be set for a 128 or 64 gain; channel B has a fixed 32 gain
00083      * depending on the parameter, the channel is also set to either A or B
00084      * Ensures that gain_ = 128, 64 or 32
00085      * @param gain 128, 64 or 32
00086      */
00087     void setGain(uint8_t gain = 128);
00088 
00089     /**
00090      * Obtain current gain
00091      * @return gain_
00092      */
00093     uint8_t getGain() { return _mode; }
00094 
00095     /**
00096      * Get sensor's analog power supply voltage
00097      * @return power supply voltage
00098      */
00099     float getAvdd() { return _avdd; }
00100 
00101     /**
00102      * Sets the chip's input offset drift
00103      * @param drift The input offset drift [mV]
00104      */
00105     void setDrift(float drift = 0) { _drift = drift; }
00106 
00107     /**
00108      * Gets chip's input offset drift
00109      * @return Chip's input offset drift [mV]
00110      */
00111     int getDrift() { return(_drift); }
00112 
00113 private:
00114     float       _avdd;      // analog power supply voltage [V]
00115     DigitalOut  _sck;       // HX711 clock input line
00116     DigitalIn   _dout;      // HX711 data output line
00117     uint8_t     _gain;      // amplification factor of HX711
00118     uint8_t     _mode;      // operating mode of HX711
00119     float       _drift;     // chip's input offset drift [mV]
00120 
00121     /**
00122      * @brief   Converts a 32-bit signed fixed point integer to floating point value
00123      * @note    The 32-bit unsigned integer argument represnts actually a 24-bit signed fixed point value:
00124      *          two’s complement and the LSB of the 24-bit binary number represents 1/8,388,608th of a unit).
00125      * @param   32-bit unsigned integer
00126      * @retval  Floating point value ranging from -1 to +1
00127      */
00128     float       _toFloat(uint32_t dword);
00129 
00130     /**
00131      * Converts floating point value to input voltage
00132      * @param val Floating point value ranging from -1.0 to +1.0
00133      * @return Voltage at input [V]
00134      */
00135     float toVolt(float val);
00136 };
00137 #endif