Archive for August, 2009
A little quick work with the rattle can this weekend “finished off” my revision 2 and revision 3 bike taillights. Revision three is nearly the ‘final product’ but still lacking some automatic control circuitry that I want to implement, and a few tweaks to the firmware to make it simpler to use.
I haven’t mastered cutting a straight line with the dremel yet, once the cutting wheel bites into that thin steel it goes the direction it wants to go!
I also painted the circuit boards, masking off each LED lens on the 2×8 array so they’d stay nice and bright. I also masked the smt button, the switcher and the contact springs on the battery clips. I probably didn’t need to mask the switcher – I wasn’t sure what the paint would do it it, seeing as how it’s handling quite a bit of power at a high frequency.
I’ve also posted some new videos to my youtube channel – nothing too exciting. There’s a naked revision 3 doing its thing and a side by side of 2 and 3 post paint job.
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!
The previous “I Feel Dirty” theme was getting a bit old, so I decided to change things up! This is “Under the Sea”. I notice it is formatted for 1024×768 instead of 800×600. What do you think about that? I run a high res on all my personal monitors, but working in the IT business, I know low res is still popular with a lot of people, even if they have big monitors. If I stick with the wider format, I’ll resize some of my recent pictures so they match-up with the text.
Given that broadband adoption continues to rise world wide, I’ve increased the number of posts displayed from 3 to 5. My feeling on the small number is my posts tend to have lots of pictures, and I like to minimally compress them as possible to maintain good quality. People on slower connections or slower devices might have trouble downloading several megabytes of data to render a page. I have an old pentium 3 laptop that despite my broadband connection struggles to view some modern sites. Drop me some feedback if you find more is better, or if it’s too much.
A friend pointed out that I have several unanswered questions in the comments for some of my posts. This website is my blog, a place to record my thoughts, and in the process, share them with the public. I don’t view it as a discussion forum. I welcome comments, criticisms and feedback. You can certainly post a question, and as long as it is relevant and makes sense, I’ll approve it as a comment, however, please don’t expect an answer. Really good questions usually receive a response either here or via email. If you want a discussion or debate on something you see here, pop on over to Linear’s forums: http://forums.linear1.org.
I finished my first snapled array, and they are damn impressive! I was expecting slightly better performance than the superflux, but was blown away. I haven’t come up with a method of comparing the two yet, as I don’t have a light meter. A side by side with the reflect signs outside the house would be nice, but it’s raining cats and dogs right now!
Here’s a size comparison of the snapled versus a 3mm superflux led. Both have a body measuring 7.6mm, but the snapled has those huge contacts, and a much heavier internal structure compared to the superflux. The 5mm snapled lens also looks huge compared to the superflux.
Hand soldering the snapled smt style is fairly easy – this connection lifted up on me because I was pressing down on the opposite side. Soldering the rest I just placed the led and then slid the iron in next to the contact without touching it, then fed in the solder, which sucked the contact right onto the pad like it’s supposed to.
The finished product, before washing. Once I decide on a layout I like, I’ll probably have some boards made and will try reflowing these either in a toaster over or on a skillet.
I don’t have much to say on these, other than I scored a bunch from Future for a seemingly great price.
These appear to be HEAVY DUTY leds, destined for the automotive market. They’re discontinued now, as Lumileds is pushing the all mighty rebel for every application under the sun.
Apparently lumileds marketed these leds strictly as automotive indicator grade leds. Their design guide shows a stop light made of six of these leds, spot welded in a 2 x 3 array to heavy solid aluminum buss bars instead of a typical PCB mounting. I won’t be doing any of that, but I did draw up a layout in Eagle and came up with a 2 x 8 array for my mint tin bike light.
This board is etched and waiting to be cleaned and assembled, more pics to follow!