INA219 voltage/current sensor + OLED

/*By: Randy N. Cañada, 29/11/2025
Simple Arduino, INA219 voltage/current sensor + OLED +arduino UNO

Connections:
INA219- refer to image file, SDA=A4 , SCL= A5
SSD1306  SDA = A4, SCL = A5, GND(ARDUINO)-GROUND(SSD1306),3.3VDC/5VDC(ARDUINO)-SSD1306 VCC


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*/

#include <Wire.h>
#include <Adafruit_INA219.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>

// INA219 object
Adafruit_INA219 ina219;

// OLED setup
#define SCREEN_WIDTH 128 // OLED display width, in pixels
#define SCREEN_HEIGHT 64 // OLED display height, in pixels
Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, -1);

// --- Battery thresholds (adjust for your test supply) ---
const float VBAT_MIN = 1.42;   // Example: cutoff
const float VBAT_MAX = 1.50;   // Example: full charge

int buzzer = A2;
int greenLED = 7;
int redLED = 6;

void setup() {
  Serial.begin(9600);
  pinMode(buzzer,OUTPUT);
  pinMode(greenLED,OUTPUT);
  pinMode(redLED,OUTPUT);

  // INA219 init
  if (!ina219.begin()) {
    Serial.println("Failed to find INA219 chip");
    while (1);
  }
  ina219.setCalibration_32V_2A();
  Serial.println("INA219 ready!");

  // OLED init
  if (!display.begin(SSD1306_SWITCHCAPVCC, 0x3C)) { // 0x3C is default I2C addr
    Serial.println("SSD1306 allocation failed");
    while (1);
  }
  display.clearDisplay();
  display.setTextSize(2);      // Normal 1:1 pixel scale
  display.setTextColor(SSD1306_WHITE);
  display.setCursor(0,0);
  display.println("OLED Ready");
  display.display();
  delay(1000);
}

void loop() {
  float busVoltage = ina219.getBusVoltage_V();      // Voltage across load
  float current_mA = ina219.getCurrent_mA();        // Current draw
  float power_mW = ina219.getPower_mW();            // Power consumption

  int pct = batteryPercent(busVoltage);

  // --- Serial output (3 decimal places) ---
  Serial.print("Bus Voltage: "); Serial.print(busVoltage, 3); Serial.println(" V");
  Serial.print("Current: "); Serial.print(current_mA, 3); Serial.println(" mA");
  Serial.print("Power: "); Serial.print(power_mW/1000.0, 3); Serial.println(" W");
  Serial.print("Battery %: "); Serial.print(pct); Serial.println("%");
  if (pct <= 5) {
    Serial.println("⚠️ WARNING: Battery low!");
    digitalWrite(redLED, HIGH);
    digitalWrite(greenLED, LOW);
    digitalWrite(buzzer,!digitalRead(buzzer));

  }else{
    digitalWrite(greenLED, HIGH);
    digitalWrite(redLED, LOW);
    digitalWrite(buzzer, LOW);

  }
  Serial.println("-----------------------------");

  // --- OLED output ---
  display.clearDisplay();
  display.setCursor(0,0);
  display.setTextSize(2);
  display.print("V: "); display.print(busVoltage, 2); display.println(" V");
  display.print("I: "); display.print(current_mA, 1); display.println(" mA");
  display.print("P: "); display.print(power_mW, 1); display.println(" mW");

  // ✅ Battery line
  display.fillRect(0, 48, 128, 16, SSD1306_BLACK);
  display.setCursor(0,48);
  char buffer[12];
  sprintf(buffer, "Batt:%3d%%", pct);
  display.print(buffer);

  // ✅ Trigger low battery by percentage threshold
  if (pct <= 5) {
    display.clearDisplay();
    display.setTextSize(2);
    display.setCursor(52,1);
    display.print("LOW");
    display.setCursor(28,32);
    display.print("BATTERY!");
  }
  display.display();

  delay(1000);
}

int batteryPercent(float vbat) {
  if (vbat <= VBAT_MIN) return 0;
  if (vbat >= VBAT_MAX) return 100;
  return (int)((vbat - VBAT_MIN) * 100.0 / (VBAT_MAX - VBAT_MIN));
}