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Sometimes its really important to have a stereo system for your bike. SCUL has a ‘standard’ method by which they use a 12V SLA hooked up to a car stereo which is then wired to some car speakers. It’s cheap and easy but I’m never one to leave well enough alone. Thus my ultra-light/ultra-efficient pimped-out bike stereo system:

• 2 x 7.4V 4Ah Lithium Ion Camcorder batteries = 15V at 4A = 60W of power! ($20 each)
• Class D amp. I use the TPA3001D1 you can get kits for this, I made my own PCBs cause I wanted to make at least 4 amps. Either is A-OK. up to 20W output! Is TSSOP so a pain to solder.
• Cheap MP3 player (this one was ~$10, uses MMC cards and a AAA battery) You dont want to get your iPod all dusty. Requires an MMC card, a 256M is like $25 or something.
• Speaker(s)! I recommend old car speakers. Making an enclosure for them will make them sound better but they’re sort of engineered for poor enclosure design. Cheap/thin cookpots work great and come with an attachment point even!

Because I’m using lithium ion batteries (twice the power per lb) and a class D amp (twice the efficiency, and also no heatsink to make it superheavy), the whole system (minus speakers) is 1lb. A speaker in a cheap pot as above is about 5lbs more.
Took it out of storage and tested it on a $2 speaker which promptly died from overdriving it 🙁

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OK well, now to hook them up to the big speaker. Lookin’ good!
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Here is a closeup of the board

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And the files for the PCBs, make sure to read the datasheet to see what is up with the parts, this is otherwise undocumented

• Schematic
• Board
• Library

Notes:

• I used MOLEX Micro-fit 3.0 connectors for the wiring harness. These are awesome!
• Solder directly to the camcorder plugs to avoid having to get the wierd micro-banana plugs but then…
• Wires go through a lot of stress here so use zipties for strainrelief as shown.
• You’ll need a 7.4V battery charger for LiIons. I made one using the BQ2057 chipset, or buy from your favorite online battery store. Or just give it 1/4C 8.4V with some power supply. I’ve seen people use LM317s…hey whatever works for you
• Be careful, I overdrove the two cambridge soundworks speakers (they lasted 6 days tho!). Bring extra speakers or just use big speakers so you’re safe
• Bass response sucks…thats just what you get for having a system like this.