I am troubleshooting my blimpduino in autonomous mode. I have tracked it down to the ultrasonic sensor. I am using the serial console while manually holding the assembled gondola. My ultrasonic sensor returns an altitude of 0 almost all the time. Occasionally I will get a reading of something around ~250 and then within 3 - 4 system_refresh() prints, it goes back to zero. This is regardless of what I have the sensor pointing at (the roof, the floor, or even my hand about 12" in front of it).I think I have found another issue, but it could just be my noob status with arduino. I have read the MaxSonar EZ4 datasheet and I think I have a pretty solid grasp on the timing and how to use the PW and RX ports, which is what the blimpduino code is using to get the distance reading. What has really thrown me for a loop though is that its using pin 15 as the EZ4 "RX" pin and pin 16 as the EZ4 "PW" pin. Call me crazy, but the atmega168 doesn't have digital pins 15 and 16. According to http://arduino.cc/en/Hacking/PinMapping168 it only has up to pin 13. I know the link to that chip is a different package style than the one on the blimpduino, but shouldn't the pin naming be the same? ( I was mapping blimpduino pins to the above referenced diagram using the naming found in the datasheet at http://www.atmel.com/dyn/resources/prod_documents/doc2545.pdf )For that matter, I see some of the LEDs using pins higher than 13 as well (east led is using pin 17 for example).What gives? Is there some funky pin configuration on the blimpduino or should it be like any other atmega168 arduino pinout?If all this pin stuff is correct and I just don't understand it, then why is my ultrasonic sensor acting this way?