Temperature (#63)

* integer id interpolation

* Calculate sensor temperature based on Ri

* Sensor Ri around 25C

Co-authored-by: Andrey Gusakov <dron0gus@gmail.com>

firmware/Makefile

@@ -144,6 +144,7 @@ CPPSRC = $(ALLCPPSRC) \
           pid.cpp \
           pump_control.cpp \
           uart.cpp \
+          interpolation.cpp \
           main.cpp
 
 # List ASM source files here.

firmware/interpolation.cpp

@@ -0,0 +1,37 @@
+#include "interpolation.h"
+
+int interpolateInt(int x1, int y1, int x2, int y2, int x)
+{
+	if (x1 == x2)
+		return y1;
+
+	return (y1 + (y2 - y1) * (x - x1) / (x2 - x1));
+}
+
+int interpolateIntClamped(int x1, int y1, int x2, int y2, int x)
+{
+	if (x <= x1)
+		return y1;
+	if (x >= x2)
+		return y2;
+
+	return interpolateInt(x1, y1, x2, y2, x);
+}
+
+int interpolate_1d_int(const struct inter_point *p, int size, int x)
+{
+	int i;
+
+	/* no exterpolation */
+	if (x < p[0].x)
+		return p[0].y;
+
+	for (i = 0; i < size - 1; i++) {
+		if ((x >= p[i].x) && (x < p[i + 1].x)) {
+			return interpolateInt(p[i].x, p[i].y, p[i + 1].x, p[i + 1].y, x);
+		}
+	}
+
+	/* no exterpolation */
+	return p[size - 1].y;
+}

firmware/interpolation.h

@@ -0,0 +1,10 @@
+#pragma once
+
+struct inter_point {
+	int		x;
+	int		y;
+};
+
+int interpolateInt(int x1, int y1, int x2, int y2, int x);
+int interpolateIntClamped(int x1, int y1, int x2, int y2, int x);
+int interpolate_1d_int(const struct inter_point *p, int size, int x);

firmware/sampling.cpp

@@ -1,4 +1,5 @@
 #include "sampling.h"
+#include "interpolation.h"
 
 #include "ch.h"
 #include "hal.h"
@@ -14,6 +15,27 @@ static float nernstDc = 0;
 static float pumpCurrentSenseVoltage = 0;
 static float internalBatteryVoltage = 0;
 
+static const struct inter_point lsu49_r_to_temp[] =
+{
+    {   80, 1030},
+    {  150,  890},
+    {  200,  840},
+    {  250,  805},
+    {  300,  780},
+    {  350,  760},
+    {  400,  745},
+    {  450,  730},
+    {  550,  705},
+    {  650,  685},
+    {  800,  665},
+    { 1000,  640},
+    { 1200,  630},
+    { 2500,  565},
+    { 6000,   25}   /* measured while cold */
+};
+
+#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
+
 constexpr float f_abs(float x)
 {
     return x > 0 ? x : -x;
@@ -86,6 +108,11 @@ float GetSensorInternalResistance()
     return totalEsr - VM_RESISTOR_VALUE;
 }
 
+float GetSensorTemperature()
+{
+    return interpolate_1d_int(lsu49_r_to_temp, ARRAY_SIZE(lsu49_r_to_temp), GetSensorInternalResistance());
+}
+
 float GetNernstDc()
 {
     return nernstDc;

firmware/sampling.h

@@ -4,6 +4,7 @@ void StartSampling();
 
 float GetNernstAc();
 float GetSensorInternalResistance();
+float GetSensorTemperature();
 float GetNernstDc();
 
 float GetPumpNominalCurrent();