From 4265af272a962ce1df1f6a975fdc8210f889760a Mon Sep 17 00:00:00 2001
From: Christian Franke <nobody@nowhere.ws>
Date: Tue, 10 Dec 2013 07:01:52 +0100
Subject: Add some conversions from celsius to adc values

Luckily, this ATMega is grossly oversized, so we can
just throw in floating point arithmetic.
---
 command.c    |  8 +++++---
 controller.c | 47 +++++++++++++++++++++++++++++++++++++++++------
 controller.h |  4 ++--
 fit.py       | 23 +++++++++++++++++++++++
 4 files changed, 71 insertions(+), 11 deletions(-)
 create mode 100644 fit.py

diff --git a/command.c b/command.c
index 7d8c515..09b91ec 100644
--- a/command.c
+++ b/command.c
@@ -14,7 +14,7 @@ static void handle_set(char *buffer, uint16_t len)
 	const char *success_msg = "OK Temperature set.\r\n";
 	const char *input;
 	char *endptr;
-	long temperature;
+	double temperature;
 
 	if (len < 2) {
 		serial_send(error_msg, strlen(error_msg), 0);
@@ -22,7 +22,7 @@ static void handle_set(char *buffer, uint16_t len)
 	}
 
 	input = buffer + 1;
-	temperature = strtol(input, &endptr, 10);
+	temperature = strtod(input, &endptr);
 	if (input[0] == '\r' || input[0] == '\n' ||
 			(endptr[0] != '\r' && endptr[0] != '\n')) {
 		serial_send(error_msg, strlen(error_msg), 0);
@@ -48,8 +48,10 @@ static void handle_off(char *buffer, uint16_t len)
 static void handle_get(char *buffer, uint16_t len)
 {
 	char response[128];
+	long temp = 10 * controller_get();
 
-	snprintf(response, sizeof(response), "OK t=%ld\r\n", controller_get());
+	/* printf won't print doubles on avr */
+	snprintf(response, sizeof(response), "OK t=%ld.%ld\r\n", temp/10, temp%10);
 	serial_send(response, strlen(response), 0);
 }
 
diff --git a/controller.c b/controller.c
index bde2cac..6dee4da 100644
--- a/controller.c
+++ b/controller.c
@@ -1,9 +1,13 @@
 #include <avr/io.h>
 #include <avr/interrupt.h>
+#include <math.h>
+#include <stdio.h>
+#include <string.h>
 
 #include "controller.h"
 
 #include "bridge.h"
+#include "serial.h"
 
 static void adc_init(void)
 {
@@ -40,20 +44,43 @@ void controller_init(void)
 	timer_init();
 }
 
-int controller_set(long target)
+static long celsius_to_adc(double target_temp)
 {
-	if (target < 50 || target > 974)
+	long rv;
+
+	rv = 1203.59290 * exp(-0.0686201496 * target_temp) + 413.59437;
+	if (rv > 1017)
+		return 1017;
+	if (rv < 450)
+		return 450;
+	return rv;
+}
+
+static double adc_to_celsius(long adc)
+{
+	double rv;
+
+	rv = adc - 413.59437;
+	rv /= 1203.59290;
+	rv = log(rv);
+	rv /= -0.0686201496;
+	return rv;
+}
+
+int controller_set(double target)
+{
+	if (target < 8.0 || target > 42.0)
 		return 1;
 
-	controller_target_temp = target;
+	controller_target_temp = celsius_to_adc(target);
 	controller_num_iterations = 1;
 	controller_active = 1;
 	return 0;
 }
 
-long controller_get(void)
+double controller_get(void)
 {
-	return controller_measured_temp;
+	return adc_to_celsius(controller_measured_temp);
 }
 
 void controller_off(void)
@@ -82,8 +109,16 @@ ISR(ADC_vect)
 		return;
 
 	controller_num_iterations--;
-	if (controller_num_iterations)
+	if (controller_num_iterations) {
+#if 0
+		char buffer[128];
+		snprintf(buffer, sizeof(buffer), "DEBUG adc==%ld adc_target=%ld\r\n",
+				(long int)controller_measured_temp,
+				controller_target_temp);
+		serial_send(buffer, strlen(buffer), 0);
+#endif
 		return;
+	}
 
 	controller_num_iterations = 60;
 
diff --git a/controller.h b/controller.h
index 0b65a73..70e7f30 100644
--- a/controller.h
+++ b/controller.h
@@ -2,8 +2,8 @@
 #define CONTROLLER_H
 
 void controller_init(void);
-int controller_set(long target);
-long controller_get(void);
+int controller_set(double target);
+double controller_get(void);
 void controller_off(void);
 
 #endif
diff --git a/fit.py b/fit.py
new file mode 100644
index 0000000..1ecee1f
--- /dev/null
+++ b/fit.py
@@ -0,0 +1,23 @@
+from scipy.optimize import curve_fit
+import numpy
+import matplotlib.pyplot as pyplot
+
+
+data_x = numpy.array([   10,  13,  17,  21,  24,  31,  36,  41 ])
+data_y = numpy.array([ 1017, 898, 810, 715, 620, 547, 510, 500 ])
+
+def func(x, a, b, c):
+    return a * numpy.exp(-b*x)-c
+
+popt, pcov = curve_fit(func, data_x, data_y, maxfev=5000)
+trial_x = numpy.linspace(0, 50, 200)
+trial_y = func(trial_x, *popt)
+
+print popt
+
+pyplot.figure()
+pyplot.plot(data_x, data_y, 'ro', label='Data')
+pyplot.plot(trial_x, trial_y, 'b-', label="Exp Fit")
+pyplot.legend()
+pyplot.show()
+
-- 
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