Monday, August 18, 2008
Having seen Bristlebot, I thought I knew exactly what I was looking for as I carefully disassembled my Samsung SGH-C417 phone. You see, it had accidentally gone for a ride in the washing machine and after quickly removing the battery, and then patiently letting it dry for a few days, it still wouldn't stop vibrating. Everything else worked fine, so I figured I'd open it up, find the little motor that looks like the one powering the Bristlebot, cut the wires to it, and then I'd still have a working cell phone. Here are some pics of what I saw once I opened it up: Can you see the little DC motor? I couldn't either, and as I fought with stubborn little screws and plastic tabs to uncover more of its innards, I became more frustrated with this little phone. I could still power it up and feel it vibrating the whole time, but I could not pinpoint where it was coming from. I definitely could not see a spinning motor anywhere. After a while, the last part to look under was the board with the LCD screen embedded in it. It was getting late and I couldn't see any way to carefully remove it, so in frustration I just put my screwdriver tip under it and pried. The ribbon cable to the camera lens tore and the wires to the speaker broke. The other battery or speaker looking thing remained attached and it finally caught my eye. "Could that be it?" I questioned. There was nothing under the board. "How could it be?" I agonized, but sure enough, when I connected the battery to the main board and powered on the phone, that's exactly what started vibrating. It had been in plain site within easy reach of my wire cutters from the moment I had pried apart the plastic cover, but I hadn't questioned what it was. Like the befuddled Stormtrooper, I only knew that it wasn't the DC motor I was looking for. Here's a closer look at the battery/speaker looking vibration source: After this failed repair job, I soothed my bruised embedded systems engineering ego by taking the cell phone parts to work and arraying them on my desk. As interested engineers stopped to paw through the mess I asked each of them to identify what makes it vibrate. Very few figured it out without my help, even though most of us firmware engineers have hardware experience in our past. A couple EEs where stumped for a bit too, which was very consoling. I still don't know exactly what that part is called or how it works. Is it a solenoid relay that is rapidly switched on and off? Feel free to educate me in the comments. I guess the moral of the story is to remove all pre-conceived notions when you enter a debugging task and question everything you don't understand. Or maybe it's just that you should check your pockets before putting your pants in the wash.