ISR0 bugfix

arduino/src/ultrasonic.cpp

@@ -3,7 +3,7 @@
 struct usData_t usData[2];
 
 void us_0_isr() {
-  if(digitalRead(US_RX_0_PIN) && usData[1].state == rxPending) {
+  if(digitalRead(US_RX_0_PIN) && usData[0].state == rxPending) {
     usData[0].pulseStart = TCNT1;
     usData[0].state = counting;
   } else if(usData[0].state == counting) {