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Right after Burning Man, I decided to redesign the CDAMP board to better serve the purpose I had in mind.
I added an ESD protection circuit to the PC board to keep input glitches out of the amplifier chip. I also decided that the input connector should be a 1/8" stereo jack instead of two RCA jacks, and that the board should have a USB charging port to keep the iPod charged up. I removed the earlier solar charging circuit since it didn't work well. Instead, I added a USB charger port using a 5V switching regulator chip. There is some trickery required to make the USB device realize that it's connected to a charger, since the normal method is for the computer to talk to the device over the USB data bus. It turns out that AdaFruit's Minty Boost has the same problem and they solved it with a few resistors. This change was implemented in late 2008 in the CDAMP revision B board. It worked quite well, and has been reliable for over a year. The pipe mounting problem as solved by using a standard $25 bike rear rack and attaching the 6" pipe to it with two 3/4" PVC pipe runners that fit into the wide slots on the rack. Two aluminum straps hold the PVC pipes on from below with sheet metal screws. This mounting method has proven to be quite robust, but it places a lot of strain on the rack's front clamps on a tall road bike. In late February of 2009, I wrote an Instructable page on how to build the bike boom box. People liked it, but I didn't get a lot of requests for the amplifier PC boards. |
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