coil res measure but not accurate

.vscode/arduino.json

@@ -1,5 +1,5 @@
 {
-    "port": "/dev/ttyACM27",
+    "port": "/dev/ttyACM0",
     "board": "arduino:samd:arduino_zero_native",
     "sketch": "BoxmodFirmware.ino",
     "output": "./build/"

BoxmodFirmware.ino

@@ -3,6 +3,7 @@
 #include <Adafruit_GFX.h>
 #include <Adafruit_SSD1306.h>
 #include <Fonts/FreeSans9pt7b.h>
+#include <algorithm>
 
 #define SSD1306_NO_SPLASH
 #define SCREEN_WIDTH 96
@@ -12,9 +13,12 @@
 
 #define LED_PIN 18
 
-#define batVcheckActivatePin 42
 #define batVcheckMesurePin 14
+#define batVcheckActivatePin 42
 
+#define coilVcheckMesurePin1 15
+// #define coilVcheckMesurePin2 16
+#define coilRcheckActivatePin 16
 
 
 int bat_prct = 100;
@@ -33,13 +37,20 @@ void setup() {
   // while (!SerialUSB);             // Leonardo: wait for serial monitor
   SerialUSB.println("\nBoxmodFirmware");
 
+  // debug led for fire btn
   pinMode(LED_PIN, OUTPUT);
   analogWrite(LED_PIN, 0);
 
+  // battery voltage check
   pinMode(batVcheckActivatePin, OUTPUT);
   digitalWrite(batVcheckActivatePin, HIGH);
   pinMode(batVcheckMesurePin, INPUT);
 
+  // coil restistance check
+  pinMode(coilRcheckActivatePin, OUTPUT);
+  digitalWrite(coilRcheckActivatePin, HIGH);
+  pinMode(coilVcheckMesurePin1, INPUT);
+
   if (!display.begin(SSD1306_SWITCHCAPVCC, SCREEN_ADDRESS)) {  
     SerialUSB.println(F("Échec de l'initialisation de l'écran OLED"));
     // while (true);  // Boucle infinie en cas d'échec
@@ -97,19 +108,78 @@ void checkBatteryVoltage(){
   digitalWrite(batVcheckActivatePin, LOW);
   int batv_mesure = analogRead(batVcheckMesurePin);
   digitalWrite(batVcheckActivatePin, HIGH);
-  
+  SerialUSB.print("batv_mesure: ");
-  // SerialUSB.print("batv_mesure: ");
+  SerialUSB.print(batv_mesure);
-  // SerialUSB.print(batv_mesure);
+
   double batv = (batv_mesure * 2.23/4095.0)*2;
-  // SerialUSB.print(", batv: ");
+  SerialUSB.print(", batv: ");
-  // SerialUSB.print(batv);
+  SerialUSB.print(batv);
-  // SerialUSB.println("V");
+  SerialUSB.println("V");
   // range of 3.4V to 4.1V
   bat_prct = (batv - 3.4) / (4.1 - 3.4) * 100;
   // Clamp the percentage to [0, 100]
   bat_prct = constrain(bat_prct, 0, 100);
 }
 
+void checkCoilResistance(){
+  analogReadResolution(12); // btw 0 & 4095
+  analogReference(AR_DEFAULT);
+
+  // measuring the analog input of voltage
+  digitalWrite(coilRcheckActivatePin, LOW);
+  delay(15000);
+  #define NUM_SAMPLES 30
+  int readings[NUM_SAMPLES];
+  for (size_t i = 0; i < NUM_SAMPLES; i++)
+  {
+    readings[i]= analogRead(coilVcheckMesurePin1);
+    delay(10);
+  }
+  digitalWrite(coilRcheckActivatePin, HIGH);
+  // coilV_measure = coilV_measure/range;
+  std::sort(readings, readings + NUM_SAMPLES);
+  int coilV_measure = readings[NUM_SAMPLES / 2];
+  SerialUSB.print("coilV_measure: ");
+  SerialUSB.print(coilV_measure);
+  
+  const double vref = 3.30000;
+  const double r_one = 1.070000;
+
+  // converting adc to volt
+  // 2.48/3.05 = 0.8131
+  const double adc_correction = 0.8131;
+  double v_two = (coilV_measure * vref/4095.000000) * adc_correction;
+  SerialUSB.print(", v_two: ");
+  SerialUSB.print(v_two, 6);
+  SerialUSB.print("V");
+
+  // calculate voltage accross know res
+  double v_one = vref - v_two;
+  SerialUSB.print(", v_one: ");
+  SerialUSB.print(v_one);
+  SerialUSB.print("V");
+
+  // calculate current
+  double i = v_one / r_one;
+  SerialUSB.print(", i: ");
+  SerialUSB.print(i,6);
+  SerialUSB.print("A");
+
+  // calculate Ohm
+  double r_two = v_two/ i;
+  SerialUSB.print(", r_two: ");
+  SerialUSB.print(r_two);
+  SerialUSB.println("Ohm");
+
+  // coil_res = (3.3 - v_two)-1);
+  // coil_res = (3.3 - v_two) * 14.9;
+
+  coil_res = r_two;
+  // SerialUSB.print(", coil_res: ");
+  // SerialUSB.print(coil_res);
+  // SerialUSB.println("Ohm");
+}
+
 void loop() {
   if(plusBtn.getStateOnce() == 0){
     SerialUSB.println("Plus");
@@ -135,6 +205,8 @@ void loop() {
 
   if (fireBtn.getStateOnce() == 0){
     checkBatteryVoltage();
+    delay(1000);
+    checkCoilResistance();
   }
   
 

src/Btn/Btn.cpp

@@ -17,9 +17,9 @@ void Btn::checkState(){
   }
   if ((millis() - _last_debounce_time) > _debounce_delay) {
     if (reading != _state) {
-      SerialUSB.print(_pin);
+      // SerialUSB.print(_pin);
-      SerialUSB.print(": ");
+      // SerialUSB.print(": ");
-      SerialUSB.println(_state);
+      // SerialUSB.println(_state);
       _state = reading;
     }
   }