Added PWM signal example that keeps the LED at const defined brightness

lab2/lab2_demo_pwm_const/lab2_demo_pwm_const.ino

+// PWM toega viik LEDi juhtimiseks
+#define LED_PIN 3
+
+const int brightness = 170;
+
+void setup() 
+{
+  // LEDi ereduse määrab PWM signaal
+  analogWrite(LED_PIN, brightness);
+}
+
+void loop() 
+{
+  
+}
\ No newline at end of file