added lib submodule

.gitmodules

@@ -0,0 +1,3 @@
+[submodule "lib/PCA9685-Arduino"]
+	path = lib/PCA9685-Arduino
+	url = https://github.com/NachtRaveVL/PCA9685-Arduino

include/pwm.h

@@ -13,7 +13,7 @@ class Treppe {
     uint8_t state = 0;
     uint8_t switch_state = 0;
 
-
+    // initialize with i2c-Address 0, use Wire Library
     PCA9685 pwmController;     
     uint8_t softstart_led(uint8_t led, uint16_t startval, uint16_t stopval);
     void ledsequence();

src/pwm.cpp

@@ -93,7 +93,11 @@ void Treppe::ledsequence(){
 
 void Treppe::setup(){
     pwmController.resetDevices();
-    pwmController.init();
+    
+    // Deactive PCA9685 due to LED Flickering
+    // https://github.com/NachtRaveVL/PCA9685-Arduino/issues/15
+    // see also lib/PCA9685-Arduin/PCA9685.h:204
+    pwmController.init(PCA9685_PhaseBalancer_None);
     pwmController.setPWMFrequency(200);
     Serial.println("Hello from Treppe");
     Serial.print("Treppe: initial parameters: stairs=");