From 338492d64200280f97e9c286f3ef6b7c29b82758 Mon Sep 17 00:00:00 2001
From: Juyoung <ohjuyoung1006@gmail.com>
Date: Sun, 24 Sep 2023 11:46:00 -0500
Subject: [PATCH] Thermistor_Driver

---
 devices/include/thermistor.h | 61 ++++++++++++++++++++++++++++++++++++
 devices/src/thermistor.cpp   | 22 +++++++++++++
 2 files changed, 83 insertions(+)
 create mode 100644 devices/include/thermistor.h
 create mode 100644 devices/src/thermistor.cpp

diff --git a/devices/include/thermistor.h b/devices/include/thermistor.h
new file mode 100644
index 0000000..89434cf
--- /dev/null
+++ b/devices/include/thermistor.h
@@ -0,0 +1,61 @@
+#ifndef __THERMISTOR_H__
+#define __THERMISTOR_H__
+
+#include "mbed.h"
+#include "mutexless_analog.h"
+
+/*
+    Thermistor voltage reading is converted to temperature in a two step process
+
+    1. Thermistor voltage must be converted into thermistor resistance.
+    This is done by solving the voltage divider equation (VCC and other resistor R are 
+    fixed by hardware) for the thermistor voltage
+
+    Measured Voltage = VCC * (Thermistor_Resistance) / (Thermistor_Resistance + R)
+
+    2. Thermistor resistance is converted to temperature through a best fit 
+    log curve built using the specific thermistor model's electrical characteristics.
+    This will involve a pair of magic numbers (mult_const and add_const) generated by
+    fitting a curve to a series of (resistance, temperature) points provided by manufacturer
+
+    Temperature = mult_const * log(Thermistor Resistance) + add_const
+*/
+typedef struct Thermistor_Constants {
+    float mult_const;
+    float add_const;
+} Thermistor_Constants;
+
+
+const Thermistor_Constants NCP21XM472J03RA_Constants = {
+    .mult_const = -27.06,
+    .add_const = 253.11
+};
+
+
+class Thermistor {
+  private:
+    float mult_const;
+    float add_const;
+    float vcc;
+    float R;
+    AnalogInMutexless thermVoltPin;
+
+  public:
+    /*
+        Constructor expects at least 2 arguments
+        constants: Struct of log translation function constants from structs above
+        therm_pin: Analog pin the thermistor is wired to
+
+        Optional arguments
+        R: Resistance of resistor in series with thermistor
+        vcc: Total voltage across R and thermistor
+    */
+    Thermistor(const Thermistor_Constants constants, PinName therm_pin, float R = 4700, float vcc = 3.3);
+
+    /*
+        Retrives current thermistor reading
+    */
+    float get_temperature();
+};
+
+#endif
\ No newline at end of file
diff --git a/devices/src/thermistor.cpp b/devices/src/thermistor.cpp
new file mode 100644
index 0000000..27bb22a
--- /dev/null
+++ b/devices/src/thermistor.cpp
@@ -0,0 +1,22 @@
+#include "thermistor.h"
+#include <math.h>
+
+/*
+    Initialize all parameters and pin
+*/
+Thermistor::Thermistor(const Thermistor_Constants constants, PinName therm_pin, float R, float vcc) : thermVoltPin(therm_pin) {
+    this->mult_const = constants.mult_const;
+    this->add_const = constants.add_const;
+    this->vcc = vcc;
+    this->R = R;
+}
+
+/*
+    Retrive new temperature reading
+*/
+float Thermistor::get_temperature() {
+    float therm_voltage = thermVoltPin.read() * 3.3;
+    float R_Therm = R / (vcc / therm_voltage - 1);
+
+    return mult_const * std::log(R_Therm) + add_const;
+}