added TESTING flag so can test over Serial Monitor

arduino/PayloadOK_Pro_Micro.ino

@@ -1,7 +1,14 @@
+//#define TESTING  // Uncomment to test code on Serial Monitor
+
 int counter = 0;
 int RXLED = 17;  // The RX LED has a defined Arduino pin
 
 void setup() {
+
+#ifdef TESTING
+    Serial.begin(9600);
+#endif
+
   Serial1.begin(9600);
 
   digitalWrite(RXLED, LOW);   // set the RX LED ON
@@ -14,7 +21,20 @@ void setup() {
 
 void loop() {
 
+#ifdef TESTING  // ? is sent over Serial Monitor for testing
   if (Serial.available() > 0) {
+    digitalWrite(RXLED, LOW);   // set the RX LED ON
+    TXLED0; //TX LED is not tied to a normally controlled pin so a macro is needed, turn LED OFF
+    delay(50);              // wait for a second
+    digitalWrite(RXLED, HIGH);   // set the RX LED ON
+    TXLED0; //TX LED is not tied to a normally controlled pin so a macro is needed, turn LED OFF
+    char result = Serial.read();
+    //    Serial1.println(result);
+    Serial.println("OK");
+    //  Serial1.println(counter++);
+  }
+#else  // ? is sent by Pi UART
+  if (Serial1.available() > 0) {
     digitalWrite(RXLED, LOW);   // set the RX LED ON
     TXLED0; //TX LED is not tied to a normally controlled pin so a macro is needed, turn LED OFF
     delay(50);              // wait for a second
@@ -25,6 +45,7 @@ void loop() {
     Serial1.println("OK");
     //  Serial1.println(counter++);
   }
+#endif
 
   delay(100);
 }