Build Log

Spread Sheet Disaster!

Sun, 13 Jul 2008 15:48:10 -0600

See that image? That’s the result of a tiny miscalculation back in march :-( It’s still smaller than my first try, but it was supposed to be much smaller. See the “chin” on the bottom? It’s supposed to be the same size as the smaller “forehead” above.

This mistake goes back to when I picked a new OLED display. The idea was to make the smallest possible watch with the display centered. Because the display isn’t symetrical vertically (there has to be room on one side for the chip and the electrical connector), this isn’t as simple as it would seem... in fact, it’s so hard, that Albert Einstein might have had trouble with this at age 3. So, when I messed up the calculation in Excel, I didn’t notice until it was too late.

I designed and made the PC Board in a bit of a rush to take it to the Maker’s Faire. I didn’t want to damage the screen, so I avoided handling it -- it wasn’t until I got the PC board and the screen together that I realized the problem. But, even though it’s not as aesthetically pleasing, there was still stuff to learn by continuing on (not to mention that those PC boards were expensive!).

So, I’m making a case for the second version so that I can wear it as a watch. This one will hopefully have buttons (I need to machine this), and it’ll serve as a testbed for using the accelerometer as a user interface. A lot of the components are all new (but similar to ones that I’ve used before), so I’ll be testing those. And, finally, I’ve got a much better charging system connector to try (I’ll write about this later when I get some good pictures).

This second version as an attempt at thinness & a bigger battery - it would have worked, if I hadn’t made the case so big!! I didn’t have components under the battery, so I saved 1mm of thickness. But, one drawback this left was that I had a lot of wasted space above the circuitry - hopefully I can optimize it with the new design to eliminate that waste.

Next week it’s off for a whirlwind one week/three city vacation - I’ll be attending the Hope conference in NYC (not speaking this year - I spoke at Hope 6). I’ll catch a taping of The Daily Show, then visit my parents, and then attend the wedding of a good friend.

If you’re at Hope or in NYC July 18th-21st 2008 , drop me a line! john at maushammer and then dot com. Or, look for me at the show - I’m hard to miss with my shiny red backpack.

Second PC Board & New Parts

Sat, 26 Apr 2008 22:18:34 -0600

I’ve been speeding up development so that I’ll have some more stuff to show at the Maker’s Faire next weekend (I’ll be presenting Sunday at 1:00). Since the new design is a lot more complicated, I had the PC board professionally made rather than make it myself.

I finished up the board design monday night & got the boards yesterday (it’s great how much more automated PC board manufacturing has gotten). I eagerly soldered it up this morning. I tested the power supplies before adding the rest of the circuit so that, if they had been incorrectly set, they wouldn’t have fried anything. With everything in place (except the battery), it looked like this:

It looks dirty because I used a lot of flux to make sure the solder flowed where I wanted to; this will clean off easily with alcohol. I used yellow kapton tape to hold the OLED in the correct place while I soldered it, but it doesn’t have to be there; I’m leaving it on just as extra protection against bumping while it’s out of the case. Lastly, the OLED looks really dirty because it still has a soft protective film on it.

A quick tour of the PC board: First, it’s just a little bigger than a square inch. See the vertical line slightly to the right of center? All the parts are mounted to the right of that line so that the battery can occupy the left side. By doing this, I can make the watch a millimeter thinner. Lastly, the large rectangle at the bottom is a cutout for the IC that’s part of the display. The quick-turn PC Board manufacturing I used wouldn’t allow for cutouts, so I dremeled it out -- that explains the rough edge.

Although I’ve reused a lot from previous prototypes, this board is mostly new components. Both the OLED and the processor are parts I’ve never tested before, but they’re based on older versions that I’m familiar with. Other new parts include an updated accelerometer, a better battery charger, and a new +12v power supply (although this one is basically interchangeable with the old one). New features include two buttons, static protection on the charging port, a new way of connecting the charging port (still not wireless - if I had more time, I’d investigate that), and the possibility for loading new software in to the watch without ever opening it up.

That’s a lot of updates, so I’ll cover them in a new post. But, right now my main focus* is the Maker Faire - if you’ll be there, give me an email - john at maushammer, then dot com. I’ll be there both days (& probably thursday and friday too). I’ll also be helping some friends teach soldering classes.

(* besides my family that’s visiting, and, at my full-time job, the release of some amazing software in 2 weeks)

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5/12/2008 - Maker Faire Update: I had an awesome time!!! Of course this was kindof expected because Make Magazine puts on a great show, but it always surprises me in new ways. I didn’t have a booth this year because I wanted more time to walk around and take in the other exhibitors. I was lucky to team up with the awesome folks at Evil Mad Scientist Laboratories (don’t let their name fool you - they’re fairly well tempered) and got treated to the world premier of their cool Peggy 2.0 kit. Last year I missed seeing their awesome candyfab, and this year I got to sit right next to it!. Here’s a picture of our booth.

The IEEE interviewed me about my watch - they did an excellent job of editing together my rambling descriptions - thanks! See the video here.

So, besides showing off the watch (and I’ve got a case prototype that I’ll post about), I got to meet tons of cool people from all over the world. It’s an amazing community of makers - such creativity! I also taught some soldering classes, and had an excellent student - Jake - whose first attempts were better than most professional engineers I know - he’s a natural!

Lastly, I was honored with an Editor’s Choice award from someone I really respect (that makes it all the better!), Mark Frauenfelder. We’re both members of the order of people with ridiculous last names - thanks, Mark!

If you missed the San Francisco Faire this year, there will be another one in Austin.

MP4 Watch Teardown

Fri, 4 Apr 2008 21:40:41 -0600

I love engineering, and although it’s fun to design my own stuff, it’s also fun to see how other people tackled the same challenge. The watch I’m designing is pretty unique, but there are a few others that also use an OLED display. To that end, I bought an Andalong MP4 Watch (similar to ones available from ThinkGeek) & took it apart.

This watch features a 1.5” color OLED display and plays music & videos. The screen looks awesome (the above picture is real & unretouched) and the sound quality is great. Overall, it’s nicely down, except there are two big flaws.

The first flaw is how you reset it. See these two big buttons for forward and back navigation? Don’t ever press them at the same time, or else it instantly resets and turns off!

The second flaw is important to me. This device works great as a media player, but isn’t so good at being a watch. It’s got a pretty face:

... but it’s bashful. When you’re playing music, the watch will use this as a screensaver. But, if you’re not playing music, you need to hold the play button down for 2 seconds, and then either select the time display from the menu system, or wait 15 more seconds for it to go in to the screensaver mode - it’s far easier to get my cell phone than that. If it’s not playing, it will eventually turn itself off. This timeout is adjustable, but the battery lasts only 11 hours in the time display mode.

The face of the watch is about the same size as my first watch, but it’s much thicker: 12.85 mm (vs. my watch’s thickness of 10 mm)

The case is held on with 4 small screws, which are self-tapping so they’re not too durable. The watch is also insanely *not* waterproof - I’d be afraid to sweat near it. Besides the big holes in the case, the circuit board is bare; I plan on conformally coating mine to give it a fighting chance against corrosion.

The inside is dominated by a 250 mAHr battery (my watch used a 100 mAHr battery, but it has a low-power processor and a smaller screen to drive)

Underneath that is a circuit board:

The watch is powered by a Sigmatel STMP3506 processor -- similar to the one used in the iPod Shuffle, except it adds an MP3 encoder (used for voice recording).

You can see the six buttons arranged around the edges. At the top left is the micro-usb connector used for charging and uploading music. The smaller chip at the top is the TEA5767 FM radio. To the right of that is a small microphone, and the connector for the headphones (sadly, the normal 1/8” connector didn’t fit; they use a smaller plug).

The memory is on the back of this circuit board:

The OLED display is attached at the bottom, in a method similar to what I’ll use for the second version. I’ll make my watch thinner by mounting components to only one side of the board (I’ll have a cutout for the driver chip that’s part of the OLED), and by using a thinner battery.

(I swear these are not my toes! It’s just that closeups of my
fingers look funny when squeezing something really hard!)

The design of my second PC Board is coming along... I’ve got the processor (E$1) and accelerometer (E$2) placed, but not routed yet. I copied the power supply from my first design just to make sure it fits ... I might still tweak it. I added 4 little buttons (but I’ll probably use just two because buttons are ugly). At the bottom (in blue) is the where the OLED mounts. It looks like there’ll plenty of room, but I’ve got a few extra components to add and a lot of routing to do.

The new OLED came in today - it’s tiny! I’m anxious to try it out.

OLED Overhaul

Thu, 20 Mar 2008 21:06:17 -0600

Progress continues slowly... I’ve ported the code to the final processor, but then I found out that OSRAM is getting out of the OLED business.

So, first the processor. SiLabs didn’t have a demo board for the exact processor I wanted to use, so I’ve been getting by with a similar board. It lacked two big features of the processor I wanted to use -- it had only 8KB of memory instead of 32KB, and it lacked the real-time clock that I plan on making use of.

In my original design, the processor kept track of the time. A timer would count the crystal’s vibrations, and when it reached 16,384 cycles, it would interrupt the processor. Since the crystal vibrated at 32.768 kHz, this equaled twice a second. When interrupted, the processor would increment the seconds and checked to see if it overflowed -- if it did, it was reset to zero and the minutes incremented. If the minutes reached 60, in a similar manner, it was reset and the hours were incremented.

This original design works great, but it means that the processor can never fully sleep -- otherwise it would stop keeping track of time. It also means that if it ever loses its memory (due to a reset or a bug in the code), it’ll lose the time. For a simple program, that’s fine... but the second version is going to be much more complicated, so it’ll be good to make timekeeping more robust.

The new processor offers a built-in clock, but it doesn’t keep track of hours and minutes. This clock is just a simple counter -- it’s 47 bits (meaning it counts from 0 to about 140,737,488,000,000) and counts at a rate of 16384 Hz. This means that it can measure events as small as 1/16384th of a second, and it will count up to 2^32 seconds before overflowing. That’s a lot of seconds -- 68 years, to be precise!

So, my design now keeps track of time like most heavy-duty unix-based machines. It records the number of seconds that have ellapsed since 12:00 am January 1st, 1970. I use some math to convert this count into year/month/day/hours/minutes/seconds.

In terms of hardware, it’s far easier to make a big 47-bit counter than it is to make 6 smaller counters and have them roll over at odd intervals. Software is far more adept at handling special cases like leap year than hardware. It can also better handle the error cases -- like, say, when you have 62 seconds.

Another benefit of keeping the time in only seconds is that it’s simple to tell amount of time between two events. For example, I can tell how many days old I am by subtracting the unix times of my birth and today, and then dividing by the number of seconds in a day. It might be useful for a countdown to an alarm.

On the software side, I’ve also been working on drawing big characters. I’ve got a routine that draws characters double-sized -- this way, I can reuse my small font table (768 bytes) instead of making a big-character font table (would be 3000 bytes, or 10% of all memory). I’ve also added a huge version of the digits so that I can fill most of the display with just the time. This takes an incredible amount of memory (3800 bytes!), but I’ve got a simple compression routine that will make it fit in 1900 bytes (still a lot of space!). But, these digits look really good, and this is a watch, so I think it’ll be worth it.

- - - -

The other bit of news is that I discovered that OSRAM is getting out of the OLED market. They make the display I’ve been using & issued a notice in the summer that people needed to get their orders in before they stopped production. I didn’t notice, so it’s off to find a new supplier. There seems to be plenty of manufacturers of similar displays, and because they often use the same driver chips, they’ll probably be electrically and software-compatible. But, I liked OSRAM’s product -- it was available in small quantities from Digikey, came with a datasheet, and a hacker-friendly connector.

The OSRAM’s connector (above, center) was a ribbon cable. It mated to a small connector, and that connector soldered to the PC board. By lifting a lever on the back of the connector, the ribbon could easily be removed & the two pieces worked on individually. This is great because I glued the display in to the case -- it’s easier to work on the PC board when removed.

I was worried because a lot of OLEDs glue directly to a PC board & making that connection isn’t too hobbyist-friendly. The glueing uses special equipment to simultaneously apply heat and pressure. If you mess up this process, you’ll ruin the display and the PC board. Also, if you accidently yank the OLED away from the PC board, there’s no way to fix it. But, this process is more reliable than a connector, and it doesn’t take any room. In fact, it can glue to the back of the PC Board, leaving more room for components on top. Hopefully this means I can fit either a bigger battery (and get three glorious days out of a charge!!) or make a slimmer watch.

As I looked at options, I found an even better one. It’s a flex circuit that you can solder to the PC board -- it can be mass-manufactured and be done by hand. It’s flat, but not easily removable (without desoldering). So, I’ll use this type of connector. (sorry, I couldn’t find a picture)

Because the watch is designed around the OLED (both physically and aesthetically), changing it is a major overhaul. But, with this, there is opportunity: Now that I know what to look for, I can pick a slightly different display that will work a lot better.

I’ve basically narrowed the selection down to three screens. I’ve modeled how they affect the case:

From left to right:
The current Osram display: 1.3”, 96 x 64
A full color display, 0.7”, 96 x 96 (not really considering this, but it’s neat)
A white display, 1.0”, 96 x 64
A yellow display, 1.1”, 96 x 64 <-- the frontrunner

I’ve shown lots of things in the diagrams. The blue outline is the case; the red outline is the OLED module; the yellow outline is the display area of the screen. I’ve put the modules in so that they’re exactly in the center of the watch -- but since the image isn’t in the center of the module, they’re placed in a little off-center. The space between the aqua line and the display (red line) shows the unused off-center space.

The 4th display is the frontrunner because it still has a large display, but it’s shorter (shorter = less space between the straps). This will allow the watch to be shorter, too, so it’ll fit under a sleeve better.

OSRAM-based watch: 37.8 x 37.7
frontrunner design: 35 x 33.8

... so it’s off to see if I can score some samples for a prototype.

Accelerometer is a Go

Sun, 25 Nov 2007 23:16:54 -0700

I’ve added a low-power 3-axis accelerometer to my mocked-up watch. This sensor measures tilting and shaking motions and can be used for a variety of things.

For games, the sensor will measure tilt and can act like a joystick. But, because it’s inside the watch, there is nothing to break nor look ugly. I had the Pac-Man watch as a kid (the version with a joystick) and it came with 4 detachable replacement sticks because they figured you’d break or lose them.

The accelerometer can also be used to save power and extend battery life. In some modes, you might want to shake it to turn on the display. Or, positioning the watch in a certain position (like arm outstretched in front of you rather than at your side) might turn on the display... David Forbe’s Nixie Tube watch does something like this. Lastly (my favorite), the accelerometer could be used to put the watch to sleep at night simply by setting it face down.

Here’s all the gory details on the part that I’m using:
Analog Devices ADXL330 3-axis +/-3g MEMS Accelerometer Datasheet

The highlights are:
It is incredibly small (4 x 4 x 1.45 mm)
It takes very little current (320uA, or about 1/10th of my power budget)
It’s really simple to use: give it power, and it outputs 3 voltages, each representing one axis.
It’s moderately priced - about $8 - $9 in quantities of 25-100.

The good people at Sparkfun make a breakout board that allowed me to connect up to this surface-mount part easily.

So, 320uA doesn’t sound like a lot of current -- it would run for a year on a pair of AA batteries, or two weeks with my smaller watch battery. But, I’d still like to save as much power as I can, so I’m making it so that I can turn it off when not needed. During games it’ll probably be on all the time, but while it’s sleeping it might only check once a second to see if it needs to wake up. Normally a power switch like this would require an additional transistor, but since this chip is such low power, I can use one of the microprocessor’s data lines.

I improved the original version of the code (seen at the top of the post) with a bar graph:

The missing dot in each line indicates the acceleration in each axis. The X & Y axis are relatively flat, so they are near the center (0 g). The Z axis is sitting upright, so it’s registering the gravitational acceleration from the earth -- +1 g. If the part were upside down, the dot would be on the left instead of the right.

Bonus #1 - Check out this design study for a pong watch by design student Lysandre Follet:

(click to see animated version)

It looks good, if I do say so myself :-) But, alas, it’s just a study... putting it in to production might result in some compromises. 
Bonus #2 - What’s up with “Secret Code Name” text on the screen? I’ve got a name for this second version, but it’s still hush-hush :-)