HX711.cpp

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 #include "mbed.h"
00020 #include "HX711.h"
00021 
00022 /**
00023  * Class for communication with the HX711 24-Bit Analog-to-Digital converter (ADC)
00024  * (Developed for Weigh Scales by AVIA Semiconductor but can be used generally.)
00025  * This library is based on the library at https://github.com/bogde/HX711
00026  */
00027 
00028 /**
00029  * @brief   Sets gain
00030  * @note
00031  * @param   gain Selected gain (128, 64 or 32)
00032  * @retval
00033  */
00034 void HX711::setGain(uint8_t gain)
00035 {
00036     _gain = gain;
00037 
00038     switch (gain) {
00039         case 128:   // channel A, gain factor 128
00040             _mode = 1;
00041             break;
00042 
00043         case 64:    // channel A, gain factor 64
00044             _mode = 3;
00045             break;
00046 
00047         case 32:    // channel B, gain factor 32
00048             _mode = 2;
00049             break;
00050     }
00051 
00052     _sck.write(0);
00053 }
00054 
00055 /**
00056  * @brief   Obtains digital value of measured analog input voltage.
00057  * @note    It's a 24-bit two's complement integer.
00058  * @retval  Digital value of measured analog input voltage.
00059  */
00060 uint32_t HX711::readInt()
00061 {
00062     uint32_t    value = 0;
00063     for (uint8_t i = 0; i < 24; ++i) {
00064         _sck.write(1);
00065         value = value << 1;
00066         value |= _dout.read();
00067         _sck.write(0);
00068     }
00069 
00070     // set the channel and the gain factor for the next reading using the clock pin
00071     for (unsigned int i = 0; i < _mode; i++) {
00072         _sck.write(1);
00073         _sck.write(0);
00074     }
00075 
00076     return value;
00077 }
00078 
00079 /**
00080  * @brief   Converts a 32-bit signed fixed point integer to floating point value
00081  * @note    The 32-bit unsigned integer argument represnts actually a 24-bit signed fixed point value:
00082  *          two’s complement and the LSB of the 24-bit binary number represents 1/8,388,608th of a unit).
00083  * @param   32-bit unsigned integer
00084  * @retval  Floating point value ranging from -1 to +1
00085  */
00086 float HX711::_toFloat(uint32_t dword)
00087 {
00088     if (dword & 0x800000)
00089         return(-float((~dword + 1) & 0xFFFFFF) / 8388608.0f);
00090     else
00091         return(float(dword) / 8388607.0f);
00092 }
00093 
00094 /**
00095  * @brief   Converts normalised value to voltage.
00096  * @note
00097  * @param   val     Normalised measured value (ranging from -1.0f to + 1.0f)
00098  * @retval  Input   voltage in Volts [V]
00099  */
00100 float HX711::toVolt(float val)
00101 {
00102     return((val * _avdd) / _gain / 2);
00103 }
00104 
00105 /**
00106  * @brief   Obtains HX711's input voltage in mV.
00107  * @note
00108  * @retval  Measured voltage in mV.
00109  */
00110 float HX711::read()
00111 {
00112     return(toVolt(_toFloat(readInt())) * 1000 - _drift);
00113 }