We’re changing it up this week with a reverse engineering fail which [Itay] pointed out to us. A couple of years ago [Nate] over at Sparkfun agreed to help a friend with a project that required precise distance measurement. He knew that laser rangefinders are a good way to go and mentions their use in golfing and the building trades. He picked up this handheld version billed as a laser tape measure. He put up a valiant effort to reverse engineer the PCB in hopes of finding a hook for the measurement data.
Obviously his endeavor failed or we wouldn’t be talking about it in this column. But there’s a lot to learn about his methods, and a few of the comments associated with his original post help to shed light on a couple of extra things to try.
First off, this thing isn’t cheap — ringing in for at least $90. That’s not a bad thing as the electronics are both well engineered and well designed. [Nate] was right to assume there’s some type of debugging information available from the board, he just had to find it. After spending some time with a continuity tester he was able to figure out what the test pads shown above go to and he soldered some pins onto them in order to connect his test equipment.
So what’s next? Using a logic sniffer is the next logical step in the reverse engineering process. [Nate] made a ton of captures and ended up stumbling upon a tiny snippet of serial data. The software he was using identified it as 19543 baud which is close enough to the 19200 standard to call it a match. But further efforts to send or receive more than the ‘? \n \r’ which the device was putting out failed.
So what’s going on here? Some of the ideas already posted on the original thread include the need to ground a line to get the chip talking, flow control problems, attempts at using AT commands, and the possibility that a fuse on the RX line was burnt during programming to prevent tampering/reading the firmware. Of course we’d like to hear what you think below!
Fail of the Week is a Hackaday column which runs every Wednesday. Help keep the fun rolling by writing about your past failures and sending us a link to the story — or sending in links to fail write ups you find in your Internet travels.