Updated thermistor constant.

[kokare.git] / kokare.c

diff --git a/kokare.c b/kokare.c
index b81842e..f7033d8 100644 (file)
--- a/kokare.c
+++ b/kokare.c
@@ -1,5 +1,6 @@
 #include <avr/io.h>
 #include <avr/interrupt.h>
+#include <avr/eeprom.h>
 #include <inttypes.h>
 #include <math.h>
 
@@ -227,16 +228,23 @@ void convcycle(void)
      * Theoretically:
      *  t = RC * ln(2) => R = t / (C * ln(2))
      *  R = A * exp(B / T) => T = B / ln(R / A)
-     *  T = B / ln(R / (A * C * ln(2)))
-     * In the following: 
+     *  T = B / ln(t / (A * C * ln(2)))
+     * Where:
+     *  t = The measured time (s)
+     *  R = The resistance of the thermistor (Ohm)
+     *  C = The capacitance of the capacitor (F)
+     *  T = The temperature (K)
+     *  A, B are the thermistor-specific constants
+     *
+     * In the following code:
      *  a = ttimea as float
-     *  C = 1e6 / (A * C * ln(2))
+     *  C = 1e-6 / (A * C * ln(2))
      *  ra = a * C
      *  l = ln(ra)
      *  t = B / l
      * Note, temperature is in Kelvin
      */
-#define C 9.792934
+#define C 10.819112      /* A is 0.1333469 */
 #define B 4020.0
     if(state == 0) {
        if((mnow - last > 200000) && tavgok) {
@@ -266,13 +274,21 @@ int main(void)
     int state, cur, run, rstate, delta;
     unsigned long utime;
     
-    state = 0;
-    cur = 100;
+    state = 1;
+    cur = eeprom_read_byte(0);
+    if(cur < 0)
+       cur = 0;
+    if(cur > 100)
+       cur = 100;
     run = 0;
     rstate = 0;
+    utime = getticks();
     init();
     sei();
-    display(0, 0, 0);
+    if(cur < 100)
+       display(cur, 0, 0);
+    else
+       dsp[0] = dsp[1] = SEGG;
 
     while(1) {
        mnow = getticks();
@@ -313,20 +329,22 @@ int main(void)
                    cur = 0;
                if(cur > 100)
                    cur = 100;
-               if(cur < 100) {
-                   display(cur, 0, run);
-               } else {
-                   dsp[0] = SEGG;
-                   dsp[1] = SEGG | (run?SEGP:0);
-               }
                utime = mnow;
            }
-           if(mnow - utime > 1000000)
+           if(mnow - utime > 2000000) {
                state = 0;
+               eeprom_write_byte(0, cur);
+           }
            if(sstate == 2) {
                run = !run;
                sstate = 0;
            }
+           if(cur < 100) {
+               display(cur, 0, run);
+           } else {
+               dsp[0] = SEGG;
+               dsp[1] = SEGG | (run?SEGP:0);
+           }
        } else if(state == 2) {
            /* Display raw temp time reading */
            if(ttimea < 20000) {
@@ -353,7 +371,7 @@ int main(void)
                         * ms. */
                        trdelay = 7;
                    } else {
-                       trdelay = 79 - (delta * 9);
+                       trdelay = 75 - (delta * 5);
                    }
                } else {
                    tron = 0;