Battery Packs and Defects

January 7th, 2008

Recently, someone on the chumby forum noted that the Energizer ER-PHOTO battery pack works with the chumby. The ER-PHOTO is a handy little device that essentially emulates a 12V DC wallwart with a pass-through mode, so you can continue to use whatever is plugged into the battery pack while it charges. There’s a lot of devices out there that run off of 12V and use that classic 5.5mm DC barrel jack, so they are certainly handy to have around. As you can see in the photo below, the pack consists of 3x 1800mAh Li-Ion cells, which gives a nominal capacity of 20 Wh; of course, the step-up regulator is probably only 90% efficient or so, and the circuitry in the pack is fairly simple, so maybe it lacks the electronics to safely milk the last drop out of the batteries, resulting in a reduced delivered capacity.

Scott Janousek has a nice little writeup about how you can install the battery pack inside a chumby, although I’d be more than a little bit wary about doing what he’s written up–he’s taken the raw Lithium Ion cells out of their protective plastic housing. The electrical tape wrapping won’t provide adequate protection against puncture or impact (which is possible if you’re carrying around a chumby and you drop it). This can lead to cells catching fire in a way that can’t be put out easily (only class D fire extinguishers work on these fires, and many homes and small offices have only type ABC extinguishers).

I had a “near fire” experience once where my electric Braun shaver developed a loose connection to the rechargeable cell (it’s cold-welded on, and the continuous vibration of my luggage being dragged over cobblestones in Italy eventually wore the metal tab down) so that the charging circuitry saw a substantial series resistance in its path–my guess is it was trying to do current mode charging without paying attention to the voltage–and the shaver got extremely hot and started to carbonize the potting glue used around the components. I ripped the shaver apart and sprayed the battery down with freeze-spray to keep it from going into thermal runaway. I’ve also had a few Dell Latitude battery packs get scary-hot during charging–hot potato hot, where I had to juggle it from hand to hand while I ran it to the freezer to cool it down.

At any rate, I encountered a surprising defect in an Energizer battery pack the other day. One of the folks at the chumby office got one to evaluate, charged it, but it didn’t seem to work. So I took it apart, and lo and behold, the battery terminals weren’t soldered into the motherboard. Click on the photo for a larger version of the picture, to see the defect clearly.

I’m not quite sure how this got through QA–almost certainly there is a 100% unit test at the end of the line. Maybe the tabs made just enough contact for it to pass final test, and then vibration during shipping displaced them. It’s a very scary defect, however, as loose wires in battery packs can lead to hazardous conditions.

I can definitely see how a bug like this can happen in the process; I can just imagine two operators in China sitting next to each other, one of them stuffing the terminals and the other soldering them in, and then during shift change one of the stuffed but unsoldered devices gets mixed in with the soldered batch. Most factories put controls in place to try to avoid these kinds of process omissions–but mistakes do happen. To be clear, we all live in glass houses, as mistakes sometimes happen when building chumbys as well. Whenever I see a teardown of a chumby posted on the net, I take a keen look at the photos to see if all of the procedures were followed during the construction of the chumby device.

Name that Ware December 2007

January 7th, 2008

The ware for December 2007 is shown below. Click on the image for a much larger version.

I’m guessing this ware shouldn’t be too hard. However, if anyone happens to know where I can get a datasheet for the MT8303 chip on the PCB, I’d appreciate a link. I have a high-level sense of what the chip contains but I haven’t been able to find any detailed architectural diagrams or reference manuals for the chip.

I’m also going to try something a little bit new for this competition. I’m going to stick with the original rules of Name That Ware–e.g., prizes awarded based on my personal, subjective opinion of “best analysis” merits–but for now I’m going to up the prize stakes. Now that chumbys are shipping to customers, we have a few misfit chumbys that get sent back. Thankfully, we don’t have enough of these returns to make it worthwhile to implement a rework program, so for now they just sit in inventory, gathering dust. Many of these units are “hacker-functional” e.g., a hacker would be happy to get one, but they do not meet the chumby quality standard for some cosmetic reason, such as a loose screw rattling around on the inside. I figure one of the best things we could do for these misfit chumbys is to find them a home in the hands of someone that can breathe new life into them–someone who can hack them and create something new and interesting out of them. Significantly, the unit would not come with any of the packaging or accessories that are part of the usual chumby experience–they would just be a chumby and a power supply in a brown box.

The key caveat is if you win and choose it as a prize, then you also promise not to resell the unit, since it is technically defective. I’ll be tracking the serialization information for the misfit units so we’ll know where they came from if another customer calls in with a complaint about a defective chumby they bought off of eBay. If you just intend to resell the unit, please claim one of the alternate prizes available. It’s on the honor system, so don’t be the one who ruins it for everyone else. If we start having problems (or if we run out of defective units to give away for some reason, e.g., we start a rework program), I’ll have to stop offering these as prizes!

OLPC XO-1

January 6th, 2008

I got an OLPC XO-1 a few days ago in the mail as part of the give one, get one program. Hopefully some child out there is enjoying their new laptop–there’s a certain amount of opacity in the process so I have no idea even if this laptop went to some needy far-flung village in a developing nation, as most of the propaganda would have you believe. I don’t mean to be too critical; I recognize that proper allocation of charitable resources is one of the most difficult tasks anyone can attempt, but a donation the magnitude of the laptop, even if it is only $200, is big money in the most needy countries. I somehow hesitate to think if I shouldn’t have just given a check to UNICEF instead to provide medicine to newborns. Then again, as long as one laptop is being delivered to somewhere that’s needy, I’m not doing bad compared to some other charities, where often more than half the donation is retained to cover management fees and fundraising costs. I also got a laptop out of this…so for whatever reason, Negroponte’s logic was successful in convincing me.

Well, the point of this blog isn’t to discuss the merits of charities. We like hardware, and the OLPC XO-1 is an interesting piece of hardware. There are plenty of teardowns for the OLPC XO-1 (including one on the OLPC wiki itself), so I won’t repeat the tedium of what screw comes out of where and just cut to what I thought were interesting highlights.

If I were to make one general comment about the OLPC XO-1, it’s that its mechanical design is brilliant. It’s a fairly clean-sheet redesign of traditional notebook PC mechanics around the goal of survivability, serviceability, and robustness (then again, I’ve never taken apart any of the ruggedized notebooks out there). When closed up for “travel”, all the ports are covered, and the cooling system is extremely simple so it should survive in dusty and dirty environments. Significantly, the port coverings aren’t done with rubberized end caps that you can lose or forget to put on–they are done using the wifi antennae, and the basic design causes the user to swivel them back to cover the ports when they are packing up the laptop to go. That’s thoughtful design.

The OLPC is one of the first devices to use the Li-Fe-P battery chemistry. My understanding is that it’s safer than normal Lithium Ions (and those who have been reading the chumby fora are aware of my liability and safety concerns around putting a Lithium Ion battery into any device), but it has a lower capacity.

Unlike most other laptops, the OLPC is easy to take apart and service–something important for a device you are sending to a remote region of the world. The LCD, which is shock mounted, was clearly designed to be easy to replace if it was broken–a few screws to remove, some panels to slide off, and you’re done. This is unlike my T60p, where even the trained tech who did the warranty repair on it couldn’t quite put humpty dumpty back together again.

The display is made by Chilin (which is related to Chi Mei, one of the major LCD glass manufacturers–the current chumby’s glass is made by them as well). I had the fortune of meeting Scott Song from Chilin at China FOO, and he was telling me some of the interesting yet lesser-known features about the LCD. In addition to the celebrated dual-mode monochrome/color transreflective layer stack used by the panel, it also features a removeable backlight LED bar. Aside from mechanical abuse, the most common failure mode for an LCD is the backlight burning out. Most LED backlights are rated for only about 10,000 hours–if that–and it’s expensive to trash a whole LCD for the failure of a fifty cent component. Therefore, the backlight bar was designed to be easily replaced.

I gave it a whirl on the OLPC, and it certainly lived up to its expectations. Usually, to get to the backlight bar, you have to risk destroying the LCD panel, but in this case, two screws was all it took.

I decided to fire up the backlight outside the display, and let me tell you, that sucka is bright.

Note that the photo above wasn’t taken in the dark–it’s just that the camera shutter had to tighten up so much so that the background looked dark. If I were in the third world, I probably would say screw the laptop, I’m taking the backlight bar out and lighting my home with it!

Here again is a close-up of the pixel array used by the transreflective display (click on the image for a much larger version).

One very slick thing about the OLPC software is that I can hit a button on the lower left hand corner and it will rotate the display rendering by 90 degrees each press of the button. This allows me to easily fold the display back and use it as a sunlight-readable eBook device.

Thanks in part to the low power of the Geode CPU, the design mounts the motherboard against the LCD, unlike most laptops where the motherboard is under the keyboard. This configuration has some simplicity advantages, especially considering the flexibility required by the display unit that can be flipped 180 degrees in either direction. The heatsink for the CPU consists simply of a thin metal heat spreader, which is in close proximity to the plastic casing: no cooling holes, fins, or fans to collect dust and break (notice how the Intel Classmate PC features prominent cooling holes for its under-keyboard CPU module). It also doesn’t burn your lap up while you are using it (although the display still does get quite warm when you use it–I tucked it into my jacket once to keep me warm while running around outside in the cold).

Here’s a photo of the motherboard with the heat spreader on:

And here’s a hi-res photo of it with the heat spreader off (click on the image to access the hi-res version):

Notice how both of the large BGA chips are underfilled to provide better shock and vibration robustness. I actually have never seen an underfill like this before–it seems to be oozing out of the edges–and it also doesn’t seem to be very uniform (some spots seem to have a little underfill missing). Most underfills I’m familiar with to attempt to cover every gap and void underneath a chip (which is actually a very hard process problem); maybe this is some new kind of underfilling technique that expands a little bit upon cure to help cover voids and its robust to a few missing spots. If a reader is familiar with this type of underfill technique, I’d appreciate a link to it.

Here’s the backside of the motherboard, nice and simple (again, click for the hi-res version):

And here are some detail shots, first of the camera:

And of the wifi:

A little trivia here–this is the same chipset used inside the Microsoft Xbox360 Wireless Networking Adapter.

Presumably Microsoft doesn’t use the programmable ARM core in the Marvell 88W8388 to do something as magnanimous as bringing mesh wifi networking to the third world–probably it’s used to help implement security authentication to support their high ASPs for their closed accessories and to implement Microsoft-enhanced protocol tweaks that helps lock out competitors. Engineers make guns, they don’t tell you where to point them–that’s up to the marketing guys. Hackers take these guns apart and use the barrels and stocks as tubing and lumber to build functional art. Sometimes the art includes a bigger gun or a barrel that points backwards, and often it’s up to the media to interpret what this cryptic art means. Really, most of the time, it was done just because it’s fun to make art, but that doesn’t sell copy.

The OLPC’s wifi sensitivity is really quite excellent–the dual antennae clear of the laptop’s body do wonders for sensitivity. On the other hand, I had some trouble getting the native UI to associate the OLPC to my access point, and to get it to stay there. Overall, the software on the OLPC is clever but very “appliance-like”: there are some pre-loaded applications and it’s not immediately obvious how to add new applications using the native UI (it’s hackable from the command line but that’s not very beginner-friendly). Then again, it does include some education-oriented scripting languages that kids can use to write programs, even if it does lack a local gcc installation, and it includes the basic infrastructure for chat, video, audio, and photo sharing functionalities. If anything, I think the OLPC could play an important part in helping people keep in touch better in remote parts of the world, with some software improvements in that area (I don’t have two of these so I wasn’t able to test how easy it is to share files or connect to each other over other protocols). It also didn’t have an easy way to reconfigure the keyboard to the dvorak format that I type (I probably have to go in and hack the X configuration files via the commandline) and the keyboard is not at all comfortable for adult hands to type on–maybe I will have to plug a full-sized keyboard into the USB port to do anything extensive with the device, which sort of voids the portability aspect of the laptop. Then again, the laptop was designed for children with smaller hands, and not adults like me. Wait, I’m an adult? Crap!

Finally, some screenshots of the OLPC XO-1’s OS configuration:

Interestingly, the OLPC ships with a hardware AES unit. Great for privacy, but presumably this is going to cause some troubles for the US government export controls when it comes to shipping the OLPC to certain third world countries on certain blacklists…I know I had to fill out parts of a somewhat thorny encryption questionnaire for the chumby lawyers as part of preparation for chumby’s sale.

Winner of Name that Ware November 2007

December 14th, 2007

The ware for November 2007 is shown below, taken fully apart. As you can see, the ware consists of three circuit boards.

The ware is an A+Xunchi U3 CDMA 1x RTT wireless data dongle. I paid 250 quai for this in China, lightly negotiated, and I guess I did okay because this website shows an on-line price of 290 quai. Today’s exchange rate puts 250 quai at US $33.90.

Picking the winner was a bit tough. Karl guessed the $0.50 Euro coin, but Flo got it exactly right by pointing out that there are two of them :-). I figure I might as well accept the trend that the US dollar is on its way out, and treat Euros as the currency of reference.

Seriously though, while none of the guesses got it exactly right, several got the general class of the device right (WAN data modem); in fact, EVDO is the evolution of the 1xRTT data standard, and GPRS offers comparable data rates to 1xRTT. Speaking of a shift in reference points — usually people nail my wares because they are well documented in the English-speaking world, and Google “knows all”. This actually highlights an important limitation: English speakers can’t search Chinese web pages. There are volumes of knowledge out there in Chinese that remain closed to us. As the Chinese tech sector grows, it is becoming more important to make efforts to search in Chinese. Just try searching for USB mass storage controller ASICs, or digital picture frame SoCs on Google in English, and then go and open up one of these devices and compare your findings. I bet you’ll find that the chips most frequently used in these popular devices are best searched for in Chinese.

I digress. Jered was the first to guess in this class of devices, calling it an EVDO modem, and at a price of $150. Felix is the next to guess EVDO, but finally concludes it is GPRS at $20-$30; so the price is right, and he’s got the right-generation of data technology (GPRS and 1xRTT are both 2.5G data standards). Unfortunately, Felix revises his guess to be an EVDO device (Anydata ADU-510D/Anydata ADU-610W) at a price of $250. bitrex also picks up on the EVDO modem thread as well, and guesses a price of 1 euro, but then revises the guess to a TrackStick GPS Data Logger at $100.

Normally, I think I would award the prize to the person with the best analysis, which is fundamentally the point of Name that Ware — to promote the concept of learning through reverse engineering. To that end, Felix had the best posted analysis. This doesn’t mean to say that other contestants didn’t analyze: I have to consider that I changed the rules for this instance of the contest. I had restated the rules to center around correctness, and not analysis, so perhaps some contestants did not post their thought process because it could give an edge to other readers. Ironically, I changed the rules to make the judging easier, under the assumption that multiple people would guess the exact ware outright (which is usually the case for Name that Ware), but in the end it actually made judging harder. Also, I think I have to go with only the final guess, because if I allowed multiple guesses then one could just guess lots of things randomly and increase their chance of winning. Next time, I will stick to the original “best analysis” rules, even if I’m offering a higher value prize like a chumby.

It was a tough contest to judge, but the winner is Jered! Congratulations. Please email me and let me know which color of a chumby you would like: black, brown, or white! And thanks to everyone who played. I’ll post the next ware in a couple of weeks.

Name that Ware November 2007

December 4th, 2007

The Ware for November 2007 is shown below:

I decided to play a bit with the camera angle on this one to make it a little more challenging, because the prize is extra-special this time: a chumby. You, too can be a Chumby Insider! I’ll probably do the judging within the next two weeks, to try and get the prize to the winner before Christmas! And yes, I’ll pay for shipping to you even if you’re not in the US, although you are responsible for all local duties/tariffs/taxes (some countries may levy a hefty duty on consumer electronics imports).

The prize will go to the person who has the closest guess on both the ware and the purchase price of the ware. Accuracy of the ware guess is the first criteria — a link to the exact device or naming the exact model number is considered to be a 100% match, while correctly naming the function of device is considered the weakest match that would pass the threshold for winning — and if more than one person guesses the ware accurately, then the person with the best guess on the negotiated purchase price of the ware, within “absolute-delta” rules (not “Price is Right” rules), wins. Given a tie on that, then the chronologically first poster will win, but I’d like to try and make the game less about being first to post and more about accuracy.

As usual, you may use md5sums to obfuscate your answer to prevent copy-cats, but please don’t forget to post the plaintext back on the site for your answer in about a week: I can’t judge your entry if you don’t give me the plaintext eventually!

Good luck!