COB

12 Articles

Fail Of The Week: The Case Of The Curiously Colored Streetlights

October 9, 2024 by 115 Comments

What color are the street lights in your town? While an unfortunate few still suffer under one of the awful colors offered by vapor discharge lamps, like the pink or orange of sodium or the greenish-white of mercury, most municipalities have moved to energy-saving LED streetlights, with a bright white light that’s generally superior in every way. Unless, of course, things go wrong and the lights start to mysteriously change colors.

If you’ve noticed this trend in your area, relax; [NanoPalomaki] has an in-depth and surprisingly interesting analysis of why LED streetlights are changing colors. After examining a few streetlights removed from service thanks to changing from white to purple, he discovered a simple explanation. White LEDs aren’t emitting white light directly; rather, the white light comes from phosphors coating the underlying LED, which emits a deep blue light. The defunct units all showed signs of phosphor degradation. In some cases, the phosphors seemed discolored, as if they experienced overheating or chemical changes. In other LEDs the phosphor layer was physically separated from the backing, exposing the underlying LEDs completely. The color of these damaged modules was significantly shifted toward the blue end of the spectrum, which was obviously why they were removed from service.

Now, a discolored LED here and there does not exactly constitute a streetlight emergency, but it’s happening to enough cities that people are starting to take notice. The obvious solution would be for municipalities to replace the dodgy units Even in the unlikely event that a city would get some compensation from the manufacturer, this seems like an expensive proposition. Luckily, [NanoPalomaki] tested a solution: he mixed a wideband phosphor into a UV-curable resin and painted it onto the lens of each defective LED in the fixture. Two coats seemed to do the trick.

We have to admit that we have a hard time visualizing a city employee painstakingly painting LEDs when swapping out a fixture would take an electrician a few minutes, but at least it’s an option. And, it’s something for hobbyists and homeowners faced with the problem of wonky white LEDs to keep in mind too.

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Oddball LCDs Reverse Engineered Thanks To Good Detective Work

December 12, 2023 by 5 Comments

Is there anything more discouraging to the reverse engineer than to see a black blob of epoxy applied directly to a PCB? We think not, because that formless shape provides no clue as to what chip lies beneath, and that means a lot of detective work if you’re going to figure out how to use this thing.

[Sudhir Chandra]’s detective story starts with a bunch of oddball LCDs, slim 1×32 character units rather than the more familiar 2×16 displays. Each bore the dreaded black COB blob on the back, as well as a handful of SMD components and not much else. Googling revealed no useful documentation, and the manufacturer wasn’t interested in fielding calls from a hobbyist. Reasoning that most manufacturers wouldn’t spin up a custom chip for every display, [Sudhir] assumed there was an ST7066, a common LCD driver chip, underneath the blob, especially given the arrangement of external components. But a jumper set was bodged together under this assumption didn’t get the display going.

Next up were more destructive methods, to decap the COB and see what kind of numbers might be on the chip. Sandpaper worked at first, but [Sudhir] eventually turned to the “Chips a la [Antoine]” method of decapping, which uses heat and brute force to get at the goods. This got down to the chip, but [Sudhir]’s microscope wasn’t up to the task of reading the die markings.

What eventually cracked the case was tracing out the voltages across the various external resistors and matching them up to other chips in the same family as the ST7066, plus the realization that the long, narrow epoxy blob probably covered a similarly shaped chip, which led to the culprit: an ST7070. This allowed [Sudhir] to build an adapter PCB for the displays, with plans for a custom Arduino library to talk to the displays.

This was a great piece of reverse engineering and a good detective story to boot. Hats off to [Sudhir] for sticking with it.

On the left, an image of a COB on the multimeter's PCB. On the right, a QFP IC soldered to the spot where a COB used to be, with pieces of magnet wire making connections from the QFP's pins to the PCB tracks.

Epoxy Blob Excised Out Of Broken Multimeter, Replaced With A QFP

September 25, 2022 by 16 Comments

The black blobs on cheap PCBs haunt those of us with a habit of taking things apart when they fail. There’s no part number to look up, no pinout to probe, and if magic smoke is released from the epoxy-buried silicon, the entire PCB is toast. That’s why it matters that [Throbscottle] shared his journey of repairing a vintage multimeter whose epoxy-covered single-chip-multimeter ICL7106 heart developed an internal reference fault. When a multimeter’s internal voltage reference goes, the meter naturally becomes useless. Cheaper multimeters, we bin, but this one arguably was worth reviving.

[Throbscottle] doesn’t just show what he accomplished, he also demonstrates exactly how he went through the process, in a way that we can learn to repeat it if ever needed. Instructions on removing the epoxy coating, isolating IC pins from shorting to newly uncovered tracks, matching pinouts between the COB (Chip On Board, the epoxy-covered silicon) and the QFP packages, carefully attaching wires to the board from the QFP’s legs, then checking the connections – he went out of his way to make the trick of this repair accessible to us. The Instructables UI doesn’t make it obvious, but there’s a large number of high-quality pictures for each step, too.

The multimeter measures once again and is back in [Throbscottle]’s arsenal. He’s got a prolific history of sharing his methods with hackers – as far back as 2011, we’ve covered his guide on reverse-engineering PCBs, a skillset that no doubt made this repair possible. This hack, in turn proves to us that, even when facing the void of an epoxy blob, we have a shot at repairing the thing. If you wonder why these black blobs plague all the cheap devices, here’s an intro.

We thank [electronoob] for sharing this with us!

big LED flashlight

Own The Night With This Ludicrously Bright DIY Flashlight

November 8, 2021 by 27 Comments

If you’re a flashlight person, you know that there’s little you would do to get the brightest, most powerful, most ridiculous flashlight possible. You might even decide to build yourself a ludicrously powerful flashlight, like [Maciej Nowak] did.

If you choose the DIY route, be warned that it’s probably not going to be a simple process, at least if you follow [Maciej]’s lead. His flashlight is machined out of aluminum rounds, all turned down on the lathe to form the head of the flashlight. The head is made from three parts, each of which acts as a heat sink for the five 20-Watt CREE XHP70 LED modules. The LEDs are mounted with care to thermal considerations, and wired in series to DC-DC converter that provides the necessary 30 V using a battery pack made from four 21700 Li-ion cells. The electronics, which also includes a BMS for charging the battery and a MOSFET switching module, form a tidy package that fits into the aluminum handle.

The video below shows that the flashlight is remarkably bright, with a nice, even field with no hotspots. Given the 45-minute useful life and the three-hour recharge time, it might have been nice to make it so anywhere from one to five of the LEDs could be turned on at once. Some interesting effects might be had from switching the LEDs on sequentially, too.

Given the proclivities of our community, it’s no surprise that this is hardly the first powerful flashlight we’ve seen. This one broke the 100-Watt barrier with a single COB LED, while this ammo-can version sports an even higher light output. Neither of them looks much like a traditional flashlight, though, which is where [Maciej]’s build has the edge.

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COB LED Teardown

February 15, 2019 by 15 Comments

[Big Clive] picked up some chip-on-board (COB) LEDs meant for hydroponics that were very unusual and set out to examine them on video. Despite damaging the board almost right away, he managed to do some testing on these arrays and you can see the results in the video below. He also compares it to older LED modules.

The 144 LEDs produce a lot of light. In addition to powering the device up, he also looks at the construction of the LEDs under a magnification, comparing the older style that used tiny bond wires to make connections versus the new version soldered on the board directly.

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Lessons In Disposable Design From A Cheap Blinky Ball

October 30, 2018 by 45 Comments

Planned obsolescence, as annoying as it is when you’re its victim, still has to be admired. You can’t help but stand in awe of the designer who somehow managed to optimize a product to live one day longer than its warranty period. Seriously, why is it always the next day?

The design of products that are never intended to live long enough to go obsolete must be similarly challenging, and [electronupdate] did a teardown of a cheap LED blinky toy to see what’s involved. You’ve no doubt seen these seizure-triggering silicone balls before, mostly at checkout counters and the like where they’re sold at prices many hundreds of times what it took to make them. This particular device, which seems representative of the species, has two bright LEDs, a small controller chip, a trio of button cells for power, and a springy switch to activate it. All this is mounted to a cheap scrap of phenolic resin PCB, with the controller chip and one of the LEDs covered by a blob of clear epoxy.

This teardown one-ups most others, as [electronupdate] disrobes the chip and points a microscope at the die; the video below shows just how few transistors are employed and proposes a likely circuit. Everything about this ball just oozes cheapness, and it’s likely these things cost essentially nothing to build. Which makes sense for something destined for the landfill within a week or so.

Yes, this annoying blinky-thing is low-end garbage, but there are still design lessons to be learned from it. Anything that’s built for a broad market has to be built to a price point, and understanding those constraints is important to understanding how planned obsolescence works.

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Old LED Light Bulbs Give Up Filaments For Spider Web Clock

August 1, 2018 by 41 Comments

We love it when something common gets put to a new and unusual use, especially when it’s one of those, “Why didn’t I think of that?” situations. This digital clock with a suspended display is just such a thing.

The common items in this case were “filaments” from LED light bulbs, those meant to mimic the look of clear-glass incandescent light bulbs. [Andypugh] had been looking at them with interest for a while, and realized they were perfect as the segments for a large digital clock. The frame of the clock was formed from bent brass U-channel and mounted to an oak base via turned stanchions. The seven-segment displays were laid out in the frame and the common anodes of the LED filaments were connected together, with the cathode for each connected to a very fine wire. Each wire was directed through a random hole in the frame and channeled down into the base, to be hooked to one of the four DS8880 VFD driver chips. The anode wires form a lacy filigree behind the segments, which catch the light and make then look a little like a spider’s web. It looks great, but nicht für der gefingerpoken – the frame is at 80 VDC to drive the LED segments. The clock is synced to the UK atomic clock with a 60-kHz radio link; see the long, painful sync process in the video below.

We like the open frame look, which we’ve seen before with an equally dangerous sculptural nixie clock. And this gives us some ideas for what to do with those filament LEDs other than turning them back into a light bulb. And if [Andy] sounds familiar, it could be because he’s appeared here before. First of all resurrecting the parts bin for an entire classic motorcycle marque, and then as the designer of SMIDSY, a robot competitor in the first incarnation of the UK Robot Wars series.

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