It works, but at low resolution...

src/main.cpp

@@ -0,0 +1,18 @@
+#include <Arduino.h>
+
+// put function declarations here:
+int myFunction(int, int);
+
+void setup() {
+  // put your setup code here, to run once:
+  Serial.begin(115200);
+  pinMode(4,OUTPUT);
+}
+
+void loop() {
+  Serial.write("#");
+  digitalWrite(4,HIGH);
+  delay(500);
+  digitalWrite(4,LOW);
+  delay(500);
+}