Initial test setup

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diff --git a/README.md b/README.md
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+# hello-t-energy-s3
+
+Minimal test sketch for LilyGo T-Energy-S3 board.
+
+## Setup (one-time)
+
+```bash
+# Add ESP32 board manager
+arduino-cli config init
+arduino-cli config add board_manager.additional_urls https://espressif.github.io/arduino-esp32/package_esp32_index.json
+
+# Install ESP32 core
+arduino-cli core update-index
+arduino-cli core install esp32:esp32
+```
+
+## Build & Upload
+
+```bash
+# Find your port
+arduino-cli board list
+
+# Compile
+arduino-cli compile --fqbn "esp32:esp32:esp32s3:CDCOnBoot=cdc,FlashSize=16M,PSRAM=opi" .
+
+# Upload (replace /dev/ttyACM0 with your port)
+arduino-cli upload --fqbn "esp32:esp32:esp32s3:CDCOnBoot=cdc,FlashSize=16M,PSRAM=opi" --port /dev/ttyACM0 .
+
+# Monitor
+arduino-cli monitor --port /dev/ttyACM0 --config baudrate=115200
+```
+
+## Expected Output
+
+```
+Hello T-Energy-S3!
+Battery: 4200 mV
+Battery: 4200 mV
+...
+```
diff --git a/hello-t-energy-s3.ino b/hello-t-energy-s3.ino
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+// Minimal T-Energy-S3 test
+// Reads battery voltage and prints to USB serial
+
+#define BATTERY_PIN 3
+
+void setup() {
+    Serial.begin(115200);
+    delay(2000);  // Wait for USB CDC to initialize
+
+    Serial.println("Hello T-Energy-S3!");
+
+    pinMode(BATTERY_PIN, INPUT);
+    analogReadResolution(12);
+    analogSetPinAttenuation(BATTERY_PIN, ADC_11db);
+}
+
+void loop() {
+    int mv = analogReadMilliVolts(BATTERY_PIN) * 2;  // Voltage divider on board
+    Serial.printf("Battery: %d mV\n", mv);
+    delay(2000);
+}