UserButton example added

STM32/libraries/BoardExamples/examples/Discovery407VG/UserButton/UserButton.ino

@@ -0,0 +1,34 @@
+// show user button state with blinking LEDs
+// STM32F4 Discovery has one user button
+//
+// red LED:   button pressed
+// grenn LED: button not pressed
+
+#define USERBUTTON               PA0
+
+#define GREENLED                PD12
+#define ORANGELED               PD13
+#define REDLED                  PD14
+#define BLUELED                 PD15
+#define REDLEDOTGOVERCURRENT     PD5
+
+void setup()
+{
+  pinMode(USERBUTTON, INPUT); // mandatory for STM MCUs, on Arduino Uno working without
+  pinMode(GREENLED,  OUTPUT);
+  pinMode(REDLED,    OUTPUT);
+}
+
+void loop()
+{
+  if  ( digitalRead(USERBUTTON) )digitalWrite(REDLED  , HIGH);
+  else                           digitalWrite(GREENLED, HIGH);
+  
+  delay(100);
+
+  // leds off
+  digitalWrite(GREENLED, LOW);
+  digitalWrite(REDLED  , LOW);
+  
+  delay(100);
+}