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

#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 64
#define SCREEN_ADDRESS 0x3C

// --- MUX CONTROL PINS ---
const int S0 = 0; const int S1 = 1; const int S2 = 2; const int S3 = 3;
const int SIG_PIN = 26; // MUX1 (A0)

Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, -1);

void setup() {
  Wire.setSDA(6); Wire.setSCL(7); Wire.begin();
  pinMode(S0, OUTPUT); pinMode(S1, OUTPUT);
  pinMode(S2, OUTPUT); pinMode(S3, OUTPUT);
  
  analogReadResolution(10); // Standard 10-bit range (0-1023)

  if(!display.begin(SSD1306_SWITCHCAPVCC, SCREEN_ADDRESS)) for(;;);
  display.clearDisplay();
  display.setTextColor(SSD1306_WHITE);
}

void loop() {
  // Select J1 (Channel 0)
  digitalWrite(S0, LOW); digitalWrite(S1, LOW);
  digitalWrite(S2, LOW); digitalWrite(S3, LOW);
  
  delay(10); 
  int raw = analogRead(SIG_PIN);

  // Convert raw value to Voltage
  // Formula: (Raw Value / 1023.0) * 3.3 Volts
  float voltage = (raw / 1023.0) * 3.3;

  display.clearDisplay();
  
  // Header
  display.setTextSize(1);
  display.setCursor(0, 0);
  display.println("VOLTMETER MODE (J1)");
  display.println("---------------------");

  // Display Voltage
  display.setCursor(0, 25);
  display.setTextSize(2);
  display.print(voltage, 2); // Show 2 decimal places
  display.println(" V");

  // Display Raw for comparison
  display.setTextSize(1);
  display.setCursor(0, 50);
  display.print("Raw ADC: ");
  display.print(raw);

  // Visual Level Bar
  int barWidth = map(raw, 0, 1023, 0, 60);
  display.drawRect(65, 50, 60, 8, SSD1306_WHITE);
  display.fillRect(65, 50, barWidth, 8, SSD1306_WHITE);

  display.display();
  delay(100);
}