Pisrf performance fix (#309)

* performance fix

* performance fix

hardware/PiSrf/nrsrf.py

@@ -33,6 +33,12 @@ def Measure():
             Main()
     while GPIO.input(ECHO)==1:
         stop = time.time()
+        Dif = time.time() - realstart
+        if Dif > 5:
+            print("Ultrasonic Sensor Timed out, Restarting.")
+            time.sleep(0.4)
+            Main()
+
     elapsed = stop-start
     distance = (elapsed * 36000)/2
 
@@ -65,7 +71,7 @@ if len(sys.argv) > 1:
             distance = int( Measure() + 0.5 )
             if distance != OLD:
                 print(distance)
-                OLD = distance
+                OLD = distance                
             time.sleep(0.5)
         except:                     # try to clean up on exit
             print("0.0");