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Hi Changchung, I could get some original Seoul U-bin star borad for you around $9/one, it needs extra a few days to arrange.
but you may not able to choose the color bin. Mostly is WC type.
Thanks
Let me check what bin will be, tell you later.
First, what battery would you like to use?
1. For 1.2-1.5V x 3-4 cell solution.
Parallel all Seoul, drive them as hard as possible. D2DIM + resistor
2. 1-3 Li-ion soultion.
Series all Seoul, Boost driver like Fatman/maxFlex
3. 4-6 Li-ion soultion.
Series all Seoul, Buck driver like bFlex/nFlex
Multi-level driver is highly recommanded, because your light will become a "hotrod" within a few minus if all 5 Seoul run at 1A. You need to make it cooler for long run.