thermo/temperature.c

   1 /*
   2  * get voltage (drop) -> resistance => estimate temperature
   3  *
   4  * author: hackbard@hackdaworld.org
   5  */
   6
   7 #include <stdio.h>
   8 #include <string.h>
   9 #include <unistd.h>
  10 #include <sys/types.h>
  11 #include <sys/stat.h>
  12 #include <fcntl.h>
  13 #include <termios.h>
  14 #include <sys/ioctl.h>
  15 #include <errno.h>
  16 #include <math.h>
  17
  18 /*
  19  * user defineable values of used components, you want to edit this!
  20  */
  21
  22 #define COUNTER (256*256)
  23 #define PRESCALE 64
  24 #define FREQ 8000000
  25 #define CAP 0.0001
  26 #define RES_NEXT_CAP 10000
  27 #define U0 5.0
  28 #define RES_NTC 3550
  29 #define NTC_R_TO_T(x)  (-3e-5*(x)*(x)+0.2388*(x)-110.09)
  30
  31 #define MAGIC_U 0.2
  32
  33 int main(int argc,char **argv) {
  34
  35         int fd,ret;
  36         unsigned short c;
  37         unsigned int sum,count;
  38         unsigned char hl[2];
  39         double max,u_ntc,r_ntc;
  40         struct termios term;
  41
  42         if(argc!=2) {
  43                 printf("usage: %s <serial device>\n",argv[0]);
  44                 return -1;
  45         }
  46
  47         max=U0*(1.0-exp(-1.0*COUNTER*PRESCALE/FREQ/(RES_NEXT_CAP*CAP)));
  48
  49         memset(&term,0,sizeof(struct termios));
  50
  51         fd=open(argv[1],O_RDONLY);
  52         if(fd<0) {
  53                 perror("open call");
  54                 return -1;
  55         }
  56
  57         tcgetattr(fd,&term);
  58
  59         cfsetispeed(&term,B9600);
  60         cfsetospeed(&term,B9600);
  61
  62         term.c_cflag&=~PARENB;
  63         term.c_cflag&=~CSTOPB;
  64         term.c_cflag&=~CSIZE;
  65         term.c_cflag|=CS8;
  66
  67         term.c_lflag&=~(ICANON|ECHO|ECHOE|ISIG);
  68
  69         term.c_iflag&=~(IXON|IXOFF|IXANY);
  70
  71         tcsetattr(fd,TCSANOW,&term);
  72
  73         count=0;
  74         sum=0;
  75
  76         printf("\n");
  77         printf("low cost adc using analog comparator!\n");
  78         printf("-------------------------------------\n");
  79         printf("\n");
  80         printf("this piece of code:\n");
  81         printf("  - is estimating the voltage drop V at the ntc\n");
  82         printf("  - calculates the resistance R of the ntc\n");
  83         printf("  - tells us the corresponding temperature T\n");
  84         printf("\n");
  85         printf("here we go ....\n");
  86         printf("\n");
  87
  88         while(1) {
  89
  90                 ret=read(fd,hl,2);
  91                 if(ret!=2) {
  92                         perror("read 2");
  93                         return -1;
  94                 }
  95
  96                 c=(hl[0]<<8)|hl[1];
  97                 count+=1;
  98                 sum+=c;
  99
 100                 u_ntc=MAGIC_U+c*max/COUNTER;
 101                 r_ntc=u_ntc/(U0-u_ntc)*RES_NTC;
 102
 103                 printf("\rV: %f | %f [%f]  #  R: %f  #  T: %f",
 104                        c*max/COUNTER,sum*max/(count*COUNTER),u_ntc,
 105                        r_ntc,NTC_R_TO_T(r_ntc));
 106                 fflush(stdout);
 107
 108                 if(count==5) {
 109                         sum/=count;
 110                         count=1;
 111                 }
 112         }
 113
 114         close(fd);
 115
 116         return 0;
 117 }
 118