From 29a48d22a7cbbcb68f4551745a965ff9382e4ec9 Mon Sep 17 00:00:00 2001
From: Moritz Ruffer <m.ruffer@fasttube.de>
Date: Wed, 26 Mar 2025 18:17:39 +0100
Subject: [PATCH] smaller temp calc

---
 AMS_Master_Code/Core/Inc/NTC.h | 25 ++++++++-----------------
 1 file changed, 8 insertions(+), 17 deletions(-)

diff --git a/AMS_Master_Code/Core/Inc/NTC.h b/AMS_Master_Code/Core/Inc/NTC.h
index 52d8445..a47dcac 100644
--- a/AMS_Master_Code/Core/Inc/NTC.h
+++ b/AMS_Master_Code/Core/Inc/NTC.h
@@ -4,24 +4,15 @@
 #define NTC_B1 0.000300131f
 #define NTC_C1 5.08516E-06f
 #define NTC_D1 2.18765E-07f
-#define NTC_R25 10000.0f // 10k ohm at 25C
   
-#define NTC_R_DIVIDER 10000.0f
-#define NTC_V_DIVIDER 3.000f // 3V
+#define VREF 3000.0
 
-[[gnu::always_inline]]
-static inline float ntc_ohms_to_celsius(float ohms) {
-  float log_ohms = logf(ohms / NTC_R25);
+// More efficient (?) calc using:
+// R_T = R_Pullup / (V_REF / ADC - 1)
+// With R_T/R_0 and R_0 = R_T@25C
+// R_T/R_0 = 1 / V_REF / ADC - 1
+
+static inline int ntc_mv_to_celsius(int16_t adc) {
+  float log_ohms = logf(1/((VREF/adc)-1));
   return 1.0f / (NTC_A1 + NTC_B1 * log_ohms + NTC_C1 * log_ohms * log_ohms + NTC_D1 * log_ohms * log_ohms * log_ohms) - 273.15f;
-}
-
-[[gnu::always_inline]]
-static inline float ohms_from_ntc_v(float v) {
-  return (NTC_R_DIVIDER * v) / (NTC_V_DIVIDER - v);
-}
-
-[[maybe_unused]]
-static int ntc_mv_to_celsius(int mv) {
-  float v = (float)mv * 0.001f;
-  return (int)ntc_ohms_to_celsius(ohms_from_ntc_v(v));
 }
\ No newline at end of file