Dropped call: breaking down a broken cell phone
Click on any of the images below to see an extreme closeup. You'll also find links to the full-size images within the text of the article.
Ours is increasingly becoming a disposable society. For proof, you need only look at the plastic- and paper-based packaging swathing the electronics and other items we buy, as well as the food we eat, and the rapidity at which we discard both items and packaging (and fill up landfills in the process). One notable example of this discard-and-upgrade mentality is the cell phone. How many phones have you owned in the past five years?
"Several" will be the answer for most of you, I'd bet. (Confession: That's my answer, too.) Handset developers and their service-provider partners tempt you with ever-smaller, thinner, and lighter units, with bigger and more comprehensive address books, longer battery life, ever-faster Internet access, and additional features such as color- and resolution-rich screens (and multiple screens), still and video cameras, walkie-talkie functionality, and multimedia streaming and native-playback capabilities.
Symbolic of this fact, a few months back while walking two of my dogs I discovered a Sanyo MM-8300 advanced cell phone, snapped into at the clamshell hinge and lying near the curb not far from my home office. "One person's trash is another person's treasure" was my immediate thought, with Prying Eyes in mind. I don't know whether the phone got dismembered before it was tossed to the curb, as a result of its fall, or due to a post-curb-collision calamity. The exact circumstances that led to its demise are of no matter from a Prying Eyes angle, because aside from a between the two halves of the system, it's still surprisingly intact (here's what it originally looked like).
So what's under the phone's fashionable plastic skin, and how did Sanyo squeeze such a plethora of functions into a diminutive 3.35×1.85×0.97-in. (85×47×25-mm), 3.60 oz (102 g) form factor?
Here's some more vital statistics before we begin the dissection. The MM-8300 includes two displays, a 1.8-in. (diagonal), 176×220-pixel primary LCD and a 1-in., 72×72-pixel secondary LCD, each capable of resolving 64k colors. Cellular voice modes include 850-MHz AMPS, both 850- and 1900-MHz CDMA, and Sprint's Ready Link "walkie-talkie" mode. The MM-8300 also supports 1xRTT cellular data services such as WAP 2.0-compatible browsing. The flash illumination-inclusive embedded camera captures VGA (640×480-pixel) still images, along with video streams of up to 30 seconds' duration in two resolution options, 176×144 and 128×96 pixels. Java (J2ME) and 3D graphics capabilities provide numerous application opportunities. The MM-8300 also supports Sprint's streaming audio and video services.
The hardest part of this project was initially getting into the guts of the phone. As you can see from , Sanyo used a nonstandard screw-head design. Fortunately, an overseas outfit named Cell Phone Shop carries the necessary tool and, after a mercifully brief order-to-delivery delay, I was off and running.
I first focused my attention on the bottom half of the phone, which includes the keypad. Removing the two screws and plastic tabs that held the halves together resulted in these . Qualcomm chips form the silicon foundation of the phone's design. The MSM6100 application processor (under the thermal pad), RFL6000 low-noise amplifier, RFR6000 RF-to-receive-baseband converter, RFT6100 transmit-baseband-to-RF converter, and PM66x0 power management IC. (If indeed that's what the cryptically-labeled "BH6318GL" chip is; the package type and dimensions are a match.) Another cryptically labeled (under the ROM-code sticker) chip is, I suspect, a multi-die stacked combination of RAM and flash memory.
Note the abundance of passive components on the densely-packed circuit board. I can't tell how many internal trace layers there are, but judging from what's on top, there are several. Analog and digital subsystems are electrically isolated from each other to mitigate interference effects. By mentally flipping the board over and placing it over its mating half of the system, you can figure out where the antenna makes connection with the circuit board. And what about those five mysterious prongs at the bottom of the phone, below the MSM6100? They mate up with the battery when it's installed. shows the underside of the PCB. It's almost completely component-free; the connections to the keypad buttons dominate the surface area. You can also see the detached microphone.
Now let's turn our attention to the "flip" part of the phone, containing the camera/flash module and dual LCDs. Step 1 was to jam a jeweler's screwdriver underneath the "accent plate" (available in six fashionable colors!) and pry it away, exposing the underneath. Remove them and you end up with of the former whole flip (or, depending on your perspective, two quarters of the original whole phone). There's little to say about the speakerphone side but, as you can already tell from the picture, the other side of the flip assembly is a marvel of mechanical engineering.
Disengage a few plastic tabs and you can detach the from the (note in the latter picture the comparatively small speaker for close-proximity-to-ear, versus speakerphone, use). The next step is to free the ; by looking back at you can see where it mated with its dual-LCD symbiotic partner and, in doing so, handled both camera and LCDs' communication with the other half of the phone. You're left with , mated by several levels of (note the dedicated backlight signals for both LCDs), which wind their and are held in place by and . Amazing. Absolutely amazing.
The above is an extended version of an article that appeared in shorter form in the print edition of EDN. ThisPDF fileshows the printed version.