justDIY Project Log

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!

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Nothing much new on a technical note. I do have a new pcb layout ready to iron on to some blank copper, should get that done this weekend. I ordered more switchers and LEDs from Future on Wednesday. Originally I was excited, the estimated delivery date was 8/21. However, it has now been pushed to 8/26, oh well!

Here are some new pictures, and some video worth posting in the blog:

This is my new 2010 Trek 3700 Mountain Bike… I’ve upgraded to alloy pedals and a super tough downhill rim for the rear wheel. I had been buying cheap-o department store bikes, on average two or three per year and trashing them basically riding on streets and trails. So I wanted to upgrade to something that should hold up a bit better.

Same composure, dialed down the flash output and decreased the shutter speed a little.

Video “tour” of the bike with both lights going.

Strobe effects demonstration on some reflective signs near my house. Sorry for the wind noise, a storm is rolling in!

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I started this project a little more than a year ago, but shelved it because it wasn’t working right and I didn’t have the correct components. It was a seasonal project that would have little use over the winter, so I sort of forgot about it.

This year I’ve been going on a lot of bike rides with friends, sometimes on public roadways, sometimes after dark. My bike has a nine watt 500 some odd lumen headlight, which makes it easy to see where I’m going, and definitely makes me visible head on. The tail of my bike however still has the stock reflector, plus the little reflector stripes in my shoes, not exactly high visibility. Not wanting to pale in comparison to the headlight, the taillight is a three watt 140 lumen beast powered by three AA rechargeable batteries.

The light is based on a boost converter from National Semiconductor, the LM3410. I’m using the 525kHz SOT-23 version, the LM3410Y. Originally I had trouble with the chip self destructing, as discussed on the Linear1 forums. It was hypothesized either the inductor was underrated or the diode was too slow. Ordering parts for another project later in 2008, I bought some better inductors and diodes, which more closely resembled the specs of parts used in National’s web bench simulator. So, lacking sufficient rear light, I rekindled this project and have a “working prototype” that’s gone on two rides with me so far.

The basic function is fairly simple. The 3410 is a constant current boost (step-up) driver. A small inductor is used to ramp up the input voltage, from 3.6vdc nominal to 15.4v at approximately 200mA. The current is monitored by a one ohm resistor. A pair of output capacitors help smooth out the ripple and an input capacitor helps the batteries cope with the high demand current (as high as 1.5a in some cases). I’m using nickle metal hydride batteries, which have a rather low internal resistance – they’re designed for high demand applications and when fresh, barely sag at all under the load.

Originally I had planned on carrying the batteries directly on the PCB, using some through-hole spring clip battery holders I found in the Sparkfun library. However, AA batteries must be bigger in Colorado than they are in Michigan, because using Sparkfun’s layout gave me about a quarter inch gap between the spring and the battery. The pads were also woefully undersized for physically mounting the clip and holding it securely enough to survive the stress of batter insertion and extraction. So I dropped their layout and drew my own that looks exactly like it, but is based on measurements from a real AA battery.

Along for the ride is a Microchip PIC microcontroller, the 12F683. It provides a bit of user interface for the light, creating different blink patterns as well as putting the light into a “stand by” mode, with the switcher shut down. I’ve programmed several blinking patterns, and somewhat organized them into “modes” which I can select using the little button.

A year ago, I didn’t have any sort of enclosure in mind. The led array was assembled on a ‘standard’ sized protoboard, so I probably thought about using a plastic or aluminum prototype enclosure. However, this year, I was thinking it would be a nice fit for a large mint tin. After printing out some mock-ups and messing around with battery configurations, I settled on using three batteries and having the electronics crammed into one side of the tin with the led array mounted in the lid of the tin. This setup might have worked, except for the battery snafu. I’m using a plastic three cell holder right now, and the extra thickness it adds is preventing the lid from completely closing. It closes enough that the light is easily held shut by some big rubberbands, and it survived bouncing around under my seat for two short rides. The next revision will have the battery situation resolved and I might have a better mounting solution by then too.

Overall I’m very pleased with the outcome of this project. I have more parts on order to make a few more lights for my other bikes and friends, and I want to experiment with other array configurations and colors. There are a two videos of the light on my youtube channel, but they’re nothing to get excited about.

Thanks for reading!

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I was trying come up with something impressive to write about, after having the blog dormant since July. I tossed around a lot of different ideas… Although I haven’t been writing, I’ve been dabbling in a number of different projects. None of them are really in a state I’m ready to write about. That brings me to something I saw a few months ago on MAKE:. Bre and associates had constructed a simple 3x3x3 led cube, re-purposing a POV toy to drive the leds.

I figured this would be a good easy project I could finish in a day, so I drilled out a piece of pine board and set to soldering up some 3mm leds. I wasn’t very careful, so the little matrices look kind of ugly, but it all works and you can’t see the wires in the dark!

It didn’t take very long to toss three of these nine led matrices together. Assembling them into a twenty-seven led cube was a bit trickier. I used some gator clips to hold parts of the cube while I soldered it. Eventually I finished all the connections and had a passable cube with fairly even spacing.

Assembling the matrix is a pretty straight forward task. All you really do is tie all the cathodes together. Each matrix will become one row in the finished cube. Electrically, the cube is built as a 3×9 array, three rows and nine columns. You could probably build it the other way around, anode rows and cathode columns, but it is easier to sink a large current than source it. I think the MAKE: software only lights one led at a time, since they’re relying on the microcontroller to both source and sink current. My design is a bit different. The mcu sources current to each anode column, and N channel fets sink current for the entire row. The N channel is easily able to sink a few amps, so the cube can light an entire row at once without having to multiplex the individual leds.

In order to keep the PCB layout simple, the connections are spread all over the place in terms of the registers inside the pic. It would have been cleaner to organize eight of the nine columns as a single 8bit register on the pic, leaving only one bit left over to deal with. Instead, I’ve created symbols for each column, and set them individually from 9bit numbers.

Each anode column is current limited by a 75 ohm resistor. The value chosen was rather arbitrary, since the leds have such a low duty cycle, a lower value would have afforded me more brightness when the cube is battery powered. I can tweak the brightness a bit in the software, changing the scan rate the rows are multiplexed at.

That’s pretty much it. I’ve found there’s not a lot you can do with only 3x3x3 and 1 color, but it’s still kind of fun. Trying to think in three dimensions while drawing the animation frames is kind of tricky. I started with excel, but that wasn’t very useful – I spent more time copy and pasting formulas than I did ‘drawing’. Luckily my buddy Dan helped me out with that. He whipped up an awesome little php script that lets you draw animations 27 leds at a time, and it formats the resulting numbers so I can copy and paste them right into the code.

There’s a few videos of the cube doing various things on my Youtube Channel. Here is perhaps the most interesting one so far.

Thanks for reading, and Happy New Year!

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I found this digging around some old forgotten directories on my web server.  It appears to be four dimly lit RGB leds.

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