diff --git a/arduino/main.ino b/arduino/main.ino
new file mode 100644
index 0000000..2ea7c88
--- /dev/null
+++ b/arduino/main.ino
@@ -0,0 +1,41 @@
+// Vehicle Voltage Monitor
+// Reads 12V-14.4V battery via voltage divider on A0
+// Outputs to Serial for PC monitoring
+
+// Pin definitions
+const int PIN_VBAT = A0;  // Vehicle voltage input (via divider)
+
+// Voltage divider constants
+// Divider: 100k upper (to Vin), 47k lower (to GND)
+// Vout = Vin * (47k / (100k + 47k)) = Vin * 0.3197
+// So Vin = Vout / 0.3197
+// At 12V: ADC sees 3.84V | At 14.4V: ADC sees 4.60V
+const float DIVIDER_RATIO = 47.0 / (100.0 + 47.0);  // ~0.3197
+const float ADC_REF = 5.0;
+const int ADC_MAX = 1023;
+
+void setup() {
+  Serial.begin(9600);
+  pinMode(LED_BUILTIN, OUTPUT);
+}
+
+void loop() {
+  // Read and calculate voltage
+  int rawAdc = analogRead(PIN_VBAT);
+  float vDivider = (rawAdc / (float)ADC_MAX) * ADC_REF;
+  float vBattery = vDivider / DIVIDER_RATIO;
+
+  // Output to serial
+  Serial.print("ADC: ");
+  Serial.print(rawAdc);
+  Serial.print(" | V_bat: ");
+  Serial.print(vBattery, 2);
+  Serial.println("V");
+
+  // Heartbeat blink
+  digitalWrite(LED_BUILTIN, HIGH);
+  delay(50);
+  digitalWrite(LED_BUILTIN, LOW);
+
+  delay(1000);  // 1Hz update rate
+}