A watch for Curiosity’s drivers

Eight long years ago, when the Martian rovers Spirit and Opportunity were steaming towards our dusty neighbor, JPL systems engineers [Julie Townsend] and [Scott Doudrick] were stuck trying to solve a very strange problem. After the twin rovers landed, the rover drivers would have to live on Mars time. Because a Martian day lasts 24 hours, 39 minutes, rover team members would have to report to work 39 minutes later than the previous day. After much cajoling, a watchmaker by the name of [Garo Anserlian] was convinced to create a mechanical watch that lost 39 minutes per day, giving the team responsible for driving Spirit and Opportunity across the Martian desert these last eight years a temporal connection to the task at hand.

Of course, a lot happens in eight years. Now we have incredibly inexpensive, fully programmable TI Chronos watch, used by [Arko] to make a wristwatch set to Martian solar time. Instead of a master watchmaker selling the slowest wristwatch ever for hundreds of dollars, staying on Curiosity time is a simple matter of reprogramming a $50 wrist-mounted computer.

The build began by taking the default firmware for the Texas Instruments EZ430 Chronos wristwatch. In its stock configuration, the Chronos takes a 32.768khz clock signal, counts out clock pulses, and increments the number of seconds every time a counter reaches 32,768.

Because a Martian Sol is 24 hours, 39 minutes and 35 seconds of Earth time, [Arko] needed to program the seconds display to change every 1.027 Earth seconds. This meant changing the seconds every 33,668.833 clock cycles, instead of the Earth-oriented 32,768 clock cycles.

There’s one small glitch with that plan: the timer in the Chronos wristwatch can’t deal with floating point numbers, meaning [Arko] had to settle for incrementing the number of seconds ever 33,668 or 33,669 clock cycles. After a bit of math, [Arko] found using a value of 33,669 would mean his Martian time watch would only lose about 2 seconds a day, a minute after 78 Martian Sols, or 8.57 Martian minutes after one Martian year.

The build only took [Arko] five hours in front of his computer, and he doesn’t consider this to be a finished product. He plans on adding a few bells and whistles such as being able to display both Earth and Mars time. Still, an awesome build if your job description includes driving a rover across the Martian plains.

Using a watch to control Ms. Pacman

Recently, [Alan] broke out the ‘ol Atari 2600 to relive his childhood with a bit of Yar’s Revenge and Adventure, but after looking at his new TI EZ430 Chronos watch, he figured he could add a bit of motion control from this classic game system. He used the accelerometer in this watch to play Ms. Pacman by tilting his wrist, an awesome build that really shows off the power of his new wrist worn device.

The watch is running stock firmware and communicates to a PC via an RF module attached to his computer’s USB port. The accelerometer data is fed into a VB.net app to convert the movements of the wrist into up, down, left, and right commands. These commands are then sent out over a serial port to an Arduino to translate those commands into something the Atari joystick port can understand.

Sure, it may be a roundabout way of playing Ms. Pacman, but considering the TI Chronos has been used for very serious work such as stopping SIDS and helping out soccer referees, we’re happy to see a more frivolous application for this neat watch.

You can check out [Alan]‘s video after the break, or get the VB and Arduino source here and here.

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