If it reads a constant 255 then it is either defective or wired incorrectly... If you are also using the 5v regulator that comes with the developer's kit make sure it is plugged in the right way round as well... I blew my 5v regulator by plugging it in reversed so this stopped my ping from functioning...

Thank you for confirming the ultrasonic detector's constant reading of 255. Is your's a 4-wire or 3-wire? Mine is a 4-wire, and I connnected D21 trigger and D22 echo per the tutorial.

T. Cotter

I had a 4 wire... reversing the echo and trigger will cause the ping to not work... But I assume you checked to make sure the ping is correctly wired? Also a stab in the dark but you might want to try another port just to be sure.... If you have a multimeter you should check the output of the voltage reg to make sure it is outputting 5V.... Remember you can't use the 4 wire ping without the voltage regulator or it die from too high of a voltage... Good news is pings are dirt cheap so if it is dead you could always order the new ping here in the store... I prefer the new ping as it has the voltage reg built in already... eBay has the 4 wire old style pings for next to nothing as well. If you want to go that route...

EZ-robot supplied a new 3-wire UD under warranty. Installed the 3-wire UD, and distance sensing and collision avoidance is working.