Shmoocon: Advanced Low Power Techniques And A Watch


Real quick question: how do you increase productivity at work? The greatest (highest paid) minds would just say: do agile or scrum or something. What’s scrum? That’s where you gather ’round every morning for a waste of time meeting that kills your every desire to be productive. A while back, [Travis Goodspeed] was stuck in some lesser circle of hell like this and in an effort to be polite by not looking at his phone too much, looked at his watch too much. This led to the creation of the Goodwatch, a new bit of hardware that replaces the guts of a Casio calculator watch with a hex editor, ISM-band radio, MSP430 disassembler, and of course an RPN calculator.

[Travis] has already introduced the GoodWatch to the world. We took a look back in December but haven’t heard anything since. His talk at Shmoocon 2018 put a little more light on how this project came to be.

The key bit of hardware in the Goodwatch is the CC430 from TI, an honestly astonishing little microcontroller that includes an LCD driver, a 16-bit MSP430 microcontroller, ADC, a surprising amount of Flash and RAM, and of course a CC1101 radio capable of transmitting in the usual ISM bands. This chip is already found in a few popular projects including the Faraday Open Source digital radio, but the real draw here is the incredible intersection of a peripheral set, low power consumption, and radio.

So, how do you clone a tiny PCB from a calculator watch? The mechanical design of this project was actually the easiest and is decidedly un-clever — just grab some calipers and draw something in a CAD package. Decoding the pinout for the LCD is quite a bit more complicated.

These LCDs have four common pins and more than two dozen segment pins. After figuring out the common pins, [Travis] didn’t really want to open up the watch dozens of times to figure out the LCD, so he simply wrote a bit of code to light up a pixel and clear a pixel. Yes, it still requires a pixel ‘map’ for each pin combination, but thanks to the MSP430’s nifty memory mapped I/O, this code is very simple and very useful once the map is complete.

Right now, [Travis] has a real, working calculator watch PCB that drops right into the Casio CA-53W watch body that nearly anyone can build for themselves. There are some caveats — the radio doesn’t work with the black wristbands because of the oxide layer, and these are miniscule QFN and 0201 components — but this is a proper RPN calculator watch that’s also a radio transmitter. It doesn’t get better than that.


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