A Guide For Driving LED Matrices

Building an LED matrix is a fun project, but it can be a bit of a pain. Usually it starts with hand-soldering individual LEDs and resistors together, then hooking them up to rows and columns so they can be driven by a microcontroller of some sort. That’s a lot of tedious work, but you can order an LED matrix pre-built to save some time and headache. You’ll still need a driver though, and while building one yourself can be rewarding there are many pitfalls and trade-offs to consider when undertaking that project as well. Or, you can consider one of a number of drivers that [deshipu] has outlined in detail.

The hangups surrounding the driver board generally revolve around the issue of getting constant brightness from LEDs regardless of how many in the row or column are illuminated at one time. Since they are typically driven one row or column at a time, the more that are on the lower the brightness each LED will have. Driver boards take different approaches to solving this problem, which usually involve a combination of high-speed scanning of the matrix or using a constant-current source in order to eliminate the need for resistors. [deshipu] outlines four popular chips that achieve these purposes, and he highlights their pros and cons to help anyone looking to build something like this.

Most of these boards will get you to an 8×8 LED matrix with no problem, with a few going a few pixels higher in either direction. That might be enough for most of our needs, but for something larger you’ll need other solutions like the one found in this 64×32 LED matrix clock. There are also even more complicated drivers if you go into extra dimensions.

Photo credit: Komatta [Public domain], from Wikimedia Commons

Sharpies and Glue Sticks Fight the Gummy Metal Machining Blues

“Gummy” might not be an adjective that springs to mind when describing metals, but anyone who has had the flutes of a drill bit or end mill jammed with aluminum will tell you that certain metals do indeed behave in unhelpful ways. But a new research paper seeks to shed light on the gummy metal phenomenon, and may just have machinists stocking up on office supplies.

It’s a bit counterintuitive that harder metals like steel are often easier to cut than softer metals; especially aluminum but also copper, nickel alloys, and some stainless steel alloys. But it happens, and [Srinivasan Chandrasekar] and his colleagues at Purdue University wanted to find out why, and what can be done about it. So the first job was to get up close and personal with the interface between a cutting tool and metal stock, to observe the dynamics of cutting. In a fascinating bit of video, they saw that softer metals tend to fold in sinuous patterns rather than breaking on defined shear planes.

Source: American Physical Society.

Having previously noted that cutting through Dykem, a common machinist’s marking fluid, changes chip formation in soft metals, the researchers tested everything from Sharpies to adhesive tape and even correction fluid, and found that they all helped to reduce the gumming action to some degree. Under their microscope they can clearly see that chips form differently once the cutting edge hits the treated surface, tending to act more brittle and ejecting rather than folding. They also noted a marked decrease in cutting force for the treated metal, and much-improved surface finish to boot.

Will Sharpies and glue sticks enter the book of old machinist’s tricks like gauge-block wringing? Only time will tell. But for now, this is a pretty fascinating bit of research that you might be able to put to the test in your shop. Let us know what you find in the comments.

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Profiles in Science: Jack Kilby and the Integrated Circuit

Sixty years ago this month, an unassuming but gifted engineer sitting in a lonely lab at Texas Instruments penned a few lines in his notebook about his ideas for building complete circuits on a single slab of semiconductor. He had no way of knowing if his idea would even work; the idea that it would become one of the key technologies of the 20th century that would rapidly change everything about the world would have seemed like a fantasy to him.

We’ve covered the story of how the integrated circuit came to be, and the ensuing patent battle that would eventually award priority to someone else. But we’ve never taken a close look at the quiet man in the quiet lab who actually thought it up: Jack Kilby.

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Custom Chips As A Service

Ages ago, making a custom circuit board was hard. Either you had to go buy some traces at Radio Shack, or you spent a boatload of money talking to a board house. Now, PCBs are so cheap, I’m considering tiling my bathroom with them. Today, making a custom chip is horrifically expensive. You can theoretically make a transistor at home, but anything more demands quartz tube heaters and hydrofluoric acid. Custom ASICs are just out of reach for the home hacker, unless you’re siphoning money off of some crypto Ponzi scheme.

Now things may be changing. Costs are coming down, the software toolchain is getting there, and Onchip, the makers of an Open Source 32-bit microcontroller are now working on what can only be called a, ‘OSH Park for silicon’. They’re calling it Itsy-Chipsy, and it’s promising to bring you your own chip for as low as $100.

The inspiration for this business plan comes from services like MOSIS that allows university classes to design their own chips on multi-project wafers. This aggregates multiple chips onto one wafer, bringing the cost of a prototype down from tens of thousands of dollars to about five thousand dollars, or somewhere around a thousand dollars a chip.

Itsy-Chipsy is taking this batch processing one step further. This is a platform that combines multiple projects on one die. That thousand dollar chip is now sixteen different projects, tied together with regulators, current sources, clocks, and process monitors. Using a 2 mm by 2 mm chip size, Itsy-Chipsy gives chip designers 350 μm of silicon using a 180 nm CMOS process. That’s enough for a basic 32-bit RISC-V microprocessor in a QFN or DIP 40 for just one hundred dollars.

This project is a contender for The Hackaday Prize — the Prize ends in November and we’d be amazed to see results by then. The Onchip team is talking to foundries, though, and it looks like there’s interest for this model in the industry. We’d guess that the best case scenario is a crowdfunding campaign for an OSH Park-like chip fab sometime in 2019. Whenever it comes, this is something we’re eagerly awaiting.

Is This The End For The C.H.I.P.?

There have been so many launches of very capable little single-board computers, that it is easy to forget an individual one among the crowd. You probably remember the C.H.I.P though, for its audacious claim back in 2015 to be the first $9 computer. It ran Linux, and included wireless connectivity, composite video output, and support for battery power. As is so often the case with ambitious startups, progress from the C.H.I.P’s creator Next Thing Co came in fits and starts.

In recent months there has been something of a silence, and now members of the community have discovered evidence that Next Thing CO are the subject of a Notice of General Assignment from Insolvency Services Group. This is followed up by the discovery that their office is available for rent.

A process called Assignment to the Benefit of Creditors is an alternative to bankruptcy proceedings yet still signals the end of a company as the service liquidates remaining assets. Despite the website and forum remaining online it appears that we may have seen the end of the C.H.I.P. and its stablemates. Hackaday has reached out to Next Thing Co for comment and will update this article if we hear back.

At the time it was launched, the C.H.I.P. was a pretty impressive product, and though it has since been eclipsed by products like the Raspberry Pi Zero, the board remains a useful item. The addition of the PocketCHIP all-in-one keyboard and display peripheral made it an instantly recognizable device, and it and its more powerful companion C.H.I.P. Pro module found their way into quite a few projects. For us the most impressive C.H.I.P. project is a retrocomputer, this miniature Apple II complete with monitor. If this really is the end for this particular little board, we’ll be sorry to see it go.

Thanks [smerrett79] for the tip.

Header image: Kiwamu Okabe [CC BY-SA 2.0].

Never Let Your Christmas Tree Run Dry, With Added Ultrasound

Winter in the parts of the Northern Hemisphere for which observing Christmas includes bringing half a forest into the house should really be divided into two seasons. No-spruce-needles-in-the-carpet season, and spruce-needles-doggedly-clinging-to-the-carpet season. Evergreen trees were not designed for indoor use, and for a hapless householder to stand any chance of keeping those needles on the branches there has to be a significant amount of attention paid to the level of the water keeping the tree hydrated.

[Evan] has paid that attention to the problem of Christmas tree hydration, and to address the shortcomings of earlier designs has come up with a low water warning using an ultrasonic rangefinder. Where previous sensor attempts based on conductive probes succumbed to corrosion or dirt build-up, this one has no contact between sensor and water.

Behind the rangefinder is a CHIP board, whose software sends a text message to his phone when the water level gets a bit low. All the software is available in the linked GitHub page, so should you wish to make your tree safe from thirst, you too can give it a try.

SMS texts are a good way to alert a tree owner, but we quite like the sensor that used the tree lights instead.

Get Down to the Die Level with this Internal Chip Repair

Usually, repairing a device entails replacing a defective IC with a new one. But if you’ve got young eyes and haven’t had caffeine in a week, you can also repair a defective chip package rather than replace it.

There’s no description of the incident that resulted in the pins of the QFP chip being ablated, but it looks like a physical insult like a tool dropped on the pins. [rasminoj]’s repair consisted of carefully grinding away the epoxy cap to expose the internal traces leading away from the die and soldering a flexible cable with the same pitch between the die and the PCB pads.

This isn’t just about [rasminoj]’s next-level soldering skills, although we’ll admit you’ve got to be pretty handy with a Hakko to get the results shown here. What we’re impressed with is the wherewithal to attempt a repair that requires digging into the chip casing in the first place. Most service techs would order a new board, or at best solder in a new chip. But given that the chip sports a Fanuc logo, our bet is that it’s a custom chip that would be unreasonably expensive to replace, if it’s even still in production. Where there’s a skill, there’s a way.

Need more die-level repairs? Check out this iPhone CPU repair, or this repair on a laser-decapped chip.

[via r/electronics]