Mint Tin Bike Light 3

I completed PCB revision three of the mint tin bike light on Tuesday, but due to lack of batteries for the camera, no pictures were taken! Luckily I’ve found and recharged a second set of batteries and the camera is once again operational.

Feature-wise, this revision adds nothing over the previous light, all the changes are in board design. Firstly, the artwork was redone using polygon pours instead of straight point to point wiring (traces). The revision two switcher was running pretty warm, mostly because it didn’t have much copper to dump the heat into.

The switcher’s ground pin is now tied directly into a very large copper pour, as are the Vin and Switch pins. Using a burning finger temperature probe, the chip remained at or below Tbody even operating in constant on mode at full power. Compared to the revision two board which saw the switcher running quite hot in constant on mode.

The current sensing resistor was moved a lot closer to the feedback pin. With a feedback voltage of 190mV, the tiny resistance of the trace was actually affecting output. Shortening the trace to roughly 1mm has helped a great deal.

Finally, the layout for the battery clips was fixed, and generous polygon pours were drawn around the pads. The spring clips are now soldered down very firmly and hold the batteries quite well. I have yet to take this unit on the trail, so we’ll see if a rubber band is required or not to retain the batteries while bouncing along.

I plan on making one more prototype before sending the design off to Custom PCB or Gold Phoenix. I think I’ll eliminate the battery clips on the chance excessive force could cause one to separate from the laminate and severely damage the pcb. I also want to try a board that hosts both driver circuit and LEDs. Additionally, I plan to add a tilt / vibration sensing switch (roller ball switch), so inactivity of the bike can be detected and the light switched off to save on batteries.

Thanks for reading!

2 Replies to “Mint Tin Bike Light 3”

  1. I am trying to find a way to hook up LEDs to make a light about 3×3 inches square, that would be battery-operated, plugged into 120v until needed. I have viewed a lot of sites, but yours is truly fascinating to me! I wish I knew more about this stuff. So …. my question: Is is feasible for me to learn what I need to know to make an LED set-up, starting from scratch; is there a place where I can go to get the info I need just to make this light, or is it something I should forget about and have it engineered? And if so, can you give me a push in the right direction?? (easy push! LOL)
    That light you made is really cool! How long are those headlights lasting on only 4 AA batteries?
    Sorry if I am a bother to you. I realize you are worlds ahead of me, but any information you will give to guide me along would be really appreciated.
    Thanks,
    Bill

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