From 04ffc37ce69bf3d8c175ddae51b0fda6d7848310 Mon Sep 17 00:00:00 2001
From: hackbard <hackbard>
Date: Thu, 18 Jan 2007 22:33:35 +0000
Subject: [PATCH] host computer tool to read from rs232 and compute temperature

---
 thermo/temperature.c | 118 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 118 insertions(+)
 create mode 100644 thermo/temperature.c

diff --git a/thermo/temperature.c b/thermo/temperature.c
new file mode 100644
index 0000000..1e3dd9e
--- /dev/null
+++ b/thermo/temperature.c
@@ -0,0 +1,118 @@
+/*
+ * get voltage (drop) -> resistance => estimate temperature
+ *
+ * author: hackbard@hackdaworld.org
+ */
+
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <termios.h>
+#include <sys/ioctl.h>
+#include <errno.h>
+#include <math.h>
+
+/*
+ * user defineable values of used components, you want to edit this!
+ */
+
+#define COUNTER (256*256)
+#define PRESCALE 64
+#define FREQ 8000000
+#define CAP 0.0001
+#define RES_NEXT_CAP 10000
+#define U0 5.0
+#define RES_NTC 3550
+#define NTC_R_TO_T(x)  (-3e-5*(x)*(x)+0.2388*(x)-110.09)
+
+#define MAGIC_U 0.2
+
+int main(int argc,char **argv) {
+
+	int fd,ret;
+	unsigned short c;
+	unsigned int sum,count;
+	unsigned char hl[2];
+	double max,u_ntc,r_ntc;
+	struct termios term;
+
+	if(argc!=2) {
+		printf("usage: %s <serial device>\n",argv[0]);
+		return -1;
+	}
+
+	max=U0*(1.0-exp(-1.0*COUNTER*PRESCALE/FREQ/(RES_NEXT_CAP*CAP)));
+
+	memset(&term,0,sizeof(struct termios));
+
+	fd=open(argv[1],O_RDONLY);
+	if(fd<0) {
+		perror("open call");
+		return -1;
+	}
+
+	tcgetattr(fd,&term);
+
+	cfsetispeed(&term,B9600);
+	cfsetospeed(&term,B9600);
+	
+	term.c_cflag&=~PARENB;
+	term.c_cflag&=~CSTOPB;
+	term.c_cflag&=~CSIZE;
+	term.c_cflag|=CS8;
+
+	term.c_lflag&=~(ICANON|ECHO|ECHOE|ISIG);
+
+	term.c_iflag&=~(IXON|IXOFF|IXANY);
+
+	tcsetattr(fd,TCSANOW,&term);
+
+	count=0;
+	sum=0;
+
+	printf("\n");
+	printf("low cost adc using analog comparator!\n");
+	printf("-------------------------------------\n");
+	printf("\n");
+	printf("this piece of code:\n");
+	printf("  - is estimating the voltage drop V at the ntc\n");
+	printf("  - calculates the resistance R of the ntc\n");
+	printf("  - tells us the corresponding temperature T\n");
+	printf("\n");
+	printf("here we go ....\n");
+	printf("\n");
+
+	while(1) {
+
+		ret=read(fd,hl,2);
+		if(ret!=2) {
+			perror("read 2");
+			return -1;
+		}
+
+		c=(hl[0]<<8)|hl[1];
+		count+=1;
+		sum+=c;
+
+		u_ntc=MAGIC_U+c*max/COUNTER;
+		r_ntc=u_ntc/(U0-u_ntc)*RES_NTC;
+
+		printf("\rV: %f | %f [%f]  #  R: %f  #  T: %f",
+		       c*max/COUNTER,sum*max/(count*COUNTER),u_ntc,
+		       r_ntc,NTC_R_TO_T(r_ntc));
+		fflush(stdout);
+
+		if(count==5) {
+			sum/=count;
+			count=1;
+		}
+	}
+
+	close(fd);
+
+	return 0;
+}
+
-- 
2.20.1