diff --git a/main.ino b/main.ino
new file mode 100644
index 00000000..bf66ae58
--- /dev/null
+++ b/main.ino
@@ -0,0 +1,35 @@
+const int LED { 17 };
+const char S_OK { 0xaa };
+const char S_ERR { 0xff };
+
+void setup() {
+    pinMode(LED, OUTPUT);
+
+    // register "on_receive" as callback for RX event
+    USBSerial.onEvent(ARDUINO_HW_CDC_RX_EVENT, on_receive);
+    USBSerial.begin(9600);
+}
+char state { USBSerial.read() };
+if (!(state == LOW || state == HIGH)) {
+    USBSerial.write(S_ERR);
+    return;
+}
+with Serial('/your/port', 9600) as ser:
+    ser.write(bytes([0x1]))
+    input()
+void on_receive(void* event_handler_arg, esp_event_base_t event_base, int32_t event_id, void* event_data) {
+    // read one byte
+    char state { USBSerial.read() };
+
+    // guard byte is valid LED state
+    if (!(state == LOW || state == HIGH)) {
+        // invalid byte received
+        // report error
+        USBSerial.write(S_ERR);
+        return;
+    }
+
+    // update LED with valid state
+    digitalWrite(LED, state);
+    USBSerial.write(S_OK);
+}