void setup() {
  Serial1.setTX(4);  // Match GP4 (TX) from diagram
  Serial1.setRX(5);  // Match GP5 (RX)
  Serial1.begin(115200);
  Serial.begin(115200);
  Serial.println("Pico ready");
}

void loop() {
  if (Serial1.available()) {
    char c = Serial1.read();
    Serial.print("From Uno: ");
    Serial.println(c);
  }

  // Send message every second
  Serial1.println("Hi from Pico");
  delay(1000);
}