A while back, I was daydreaming of a nifty wristwatch. It would have years of battery life, with an MSP430 microcontroller and RPN calculator. It would be able to receive and transmit on amateur radio frequencies, in a variety of digital modes. It would look spiffy. So I built the damned thing, and it’s called the GoodWatch.
I began by disassembling the Casio 3208 watch module from a Casio CA-53W calculator watch, and measuring its circuit board which you can see on the right. Pieces of sticky note over a pad would cause segments to fail, allowing me to learn the pinout before making my own board, shown on the left.
I then assembled a watch with this board, writing firmware libraries for the LCD, keypad, and power management.
The CC430F6137 that I chose can’t quite control all of the pixels, but with three commons and all available segment pins, I was able to get everything except for the day-of-week pixels in the upper right corner.
After that, it wasn’t much work to toss together applications. Each application consists of a quick bit of C code, with handler functions for entry, exit, and refreshing the screen.
In idle mode, the GoodWatch10 (shown on the left) can easily implement all features of the original Casio. It has ~5 years of battery life, knows days of the week for the next two thousand years, and has a handy RPN calculator.
It also has a hex editor, because no proper lady or gentleman would be caught in public without one on the wrist. Here the hex editor is diagnosing a clock fault by reading the appropriate register. (Now there’s a test case for that, of course.)
“But Travis,” you say, “What about a disassembler? What if you’re stuck in an hour-long SCRUM meeting and need to reverse engineer your watch’s firmware with pen and paper to retain your own sanity?”
An MSP430 disassembler is built-in, of course.
And while the GoodWatch10 was certainly the coolest hex editor watch to wear last month, things can be niftier. In this photo, it a GoodWatch20 is beaconing my ham radio callsign to a Yaesu 817 as Morse code.
This tiny green wire–the only cosmetic blemish of the watch–uses the stainless steel watchband as a random wire antenna. It’s not well tuned, but it gets the job done.
The firmware also includes a serial debug monitor, so after flashing firmware and a codeplug of radio frequencies, you can self-test the device or send and receive packets from the air.
The radio is based on the same CC1101 core that the GirlTech IMME used, so all the old IMME hacks are portable. My reflexive jammer for P25, Mike Ossmann’s iClicker emulator, and Samy’s OpenSesame can all be adapted to this platform.
You can’t leave the receiver idly receiving in the background for power budget reasons, but otherwise the radio is fully functional. Receive and transmit, everything from CW to 4FSK.
The codeplug is compiled from a textfile and loaded into Info Flash, where it won’t be accidentally overwritten by firmware updates. Writing a CHIRP plugin won’t be much trouble.
Firmware for the watch is written in clean C89, designed to compile with GCC on Debian/Stable with no weird third-party packages or commercial compilers. The radio features gracefully disable on watches without a 26MHz crystal.
Because it can be a pain to debug radio configurations in device firmware, the UART monitor provides easy Python access to all the radio functions. You can mock up a working prototype of your radio application in host-side python, then rather directly port to C.
Full hardware CAD and source code are available on github. PCBs will be available soon. See the wiki for assembly instructions. A lecture on the GoodWatch will be presented in the Build It track at ShmooCon 2018 in Washngton, DC the weekend of January 19th.