/*********************************************************************************
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* Copyright: (C) 2018 LingYun IoT System Studio
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* All rights reserved.
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*
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* Filename: ds18b20.c
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* Description: This file is temperature sensor DS18B20 code
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*
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* Version: 1.0.0(2018/10/14)
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* Author: Guo Wenxue <guowenxue@gmail.com>
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* ChangeLog: 1, Release initial version on "2018/10/14 12:13:26"
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*
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********************************************************************************/
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#include <stdio.h>
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#include <stdlib.h>
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#include <unistd.h>
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#include <fcntl.h>
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#include <dirent.h>
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#include <string.h>
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#include <time.h>
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#include <errno.h>
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int ds18b20_get_temperature(float *temp);
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int main(int argc, char *argv[])
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{
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float temp;
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if( ds18b20_get_temperature(&temp) < 0 )
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{
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printf("ERROR: ds18b20 get temprature failure\n");
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return 1;
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}
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printf("DS19B20 get temperature: %f ℃\n", temp);
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return 0;
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}
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/* File Content:
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pi@raspberrypi:~/guowenxue $ cat /sys/bus/w1/devices/28-041731f7c0ff/w1_slave
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3a 01 4b 46 7f ff 0c 10 a5 : crc=a5 YES
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3a 01 4b 46 7f ff 0c 10 a5 t=19625
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*/
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int ds18b20_get_temperature(float *temp)
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{
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char w1_path[50] = "/sys/bus/w1/devices/";
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char chip[20];
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char buf[128];
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DIR *dirp;
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struct dirent *direntp;
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int fd =-1;
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char *ptr;
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float value;
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int found = 0;
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if( !temp )
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{
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return -1;
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}
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/*+-------------------------------------------------------------------+
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*| open dierectory /sys/bus/w1/devices to get chipset Serial Number |
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*+-------------------------------------------------------------------+*/
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if((dirp = opendir(w1_path)) == NULL)
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{
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printf("opendir error: %s\n", strerror(errno));
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return -2;
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}
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while((direntp = readdir(dirp)) != NULL)
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{
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if(strstr(direntp->d_name,"28-"))
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{
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/* find and get the chipset SN filename */
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strcpy(chip,direntp->d_name);
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found = 1;
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break;
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}
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}
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closedir(dirp);
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if( !found )
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{
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printf("Can not find ds18b20 in %s\n", w1_path);
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return -3;
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}
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/* get DS18B20 sample file full path: /sys/bus/w1/devices/28-xxxx/w1_slave */
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strncat(w1_path, chip, sizeof(w1_path)-strlen(w1_path));
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strncat(w1_path, "/w1_slave", sizeof(w1_path)-strlen(w1_path));
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/* open file /sys/bus/w1/devices/28-xxxx/w1_slave to get temperature */
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if( (fd=open(w1_path, O_RDONLY)) < 0 )
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{
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printf("open %s error: %s\n", w1_path, strerror(errno));
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return -4;
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}
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if(read(fd, buf, sizeof(buf)) < 0)
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{
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printf("read %s error: %s\n", w1_path, strerror(errno));
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return -5;
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}
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ptr = strstr(buf, "t=");
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if( !ptr )
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{
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printf("ERROR: Can not get temperature\n");
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return -6;
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}
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ptr+=2;
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/* convert string value to float value */
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*temp = atof(ptr)/1000;
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close(fd);
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return 0;
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}
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