A Newbie Takes the SMD Challenge at Supercon

A Newbie Takes the SMD Challenge at Supercon
By Dan Maloney

First-time visitors to Disneyworld often naively think they’re going to “do” the park in three days: one day for the Magic Kingdom, one day for Epcot, and one day for everything else. It’s easy to spot such people, collapsed on a bench or dragging exhausted kids around while trying to make their way to the next must-see attraction. Supercon is something like that — a Disney-esque theme park for hackers that will exhaust you if you don’t have a plan, and if you don’t set reasonable expectations. Which is why I was glad that I set only one real goal for my first Supercon: take the SMD Soldering Challenge.

Now, while I’m pretty handy with a soldering iron, I was under no illusion that I would be at all competitive. All my soldering experience has been with through-hole components, and while I also used to doing some production soldering on fine-pitch connectors, the whole surface-mount thing is new to me. I entered mainly because I wanted to see what was possible coming in raw. At best I’d learn what my limits are, and at worst I’d fail spectacularly and provide grist for a “Fail of the Supercon” post. It’s a win either way.

Scoping It Out

I decided to get the challenge out of the way as quickly as possible, so I started sharking around the table early in the afternoon on Friday. As he did last year, Al Williams was running the station. I signed up for the 4:30 heat and hung around a bit to get enough of an idea of what to do to not embarrass myself. It looked like everything was laid out really well. Each station had a good quality soldering station, a lighted magnifier, a few hand tools like flush cutters, pliers, and the all-important tweezers, and a roll of fine solder. There were a bunch of shared tools and supplies too, like desoldering braid, solder suckers, flux pens, and an LED tester. I watched enough of the action to get an idea of the workflow.

When it came time for my heat, I settled into my station and got things squared away. They thoughtfully provided magnifier hoods so that those of us with older eye could partake, and I got mine set up just the way I like it. The rules are simple: you get five minutes to open your kit and scan for missing parts, and to ask any questions you might have. After that, it’s 35 minutes to solder up everything, and each board is graded on function, neatness, and time.

The kit is a simple blinky, powered by a coin cell with an ATtiny85 driving five LEDs. The current limiting resistors and LED footprints start at 1206 and go down to a ridiculous 0201. When I opened mine, I knew the toughest part wouldn’t be the soldering itself, it would be getting the components free from their carriers. The components were helpfully segregated by size but taped down to a piece of paper. Adhesive tape and I are old enemies, so I knew there’d be trouble.

A Man With a Plan

Not too shabby, but 0402’s my limit.

I worked out a quick strategy: tape the PCB down and start with the largest components. I’ve watched enough soldering videos on YouTube to know that flux is your friend, so I got busy with the flux pen. I added a dab of solder to one of the ATtiny85 pads and tacked that in place. It’s about this time that I noticed the soldering iron tip was not exactly ideal — a chisel point — which looked massive even next to the fine pins on the SOIC package. I was surprised by how easily the chip soldered down, likely more a testimony to the ample use of flux and the good quality solder masking on the PCB.

I decided to get the cap and the first resistor and LED soldered down to make sure I had the polarity right. I assumed that the blinky would blink even if only partially assembled, an assumption borne out once I soldered down the coin cell holder (upside down, d’oh!) and slipped the battery in. My earlier fear that getting access to the components would be the bottleneck were well-founded; just getting the cover tapes peeled off the carriers was a tedious, time-consuming job. But I kept going with the next size down, the 0805s, without much trouble.

Like a machine – an amazing 6:45 start to finish by Fred T!

Just about then, someone called time, only about 8 minutes in. Oh perfect, I thought – I’m not even a third of the way done. But as I said, I wasn’t trying to be competitive, so I shrugged it off and kept going. The 0603s were a little tougher, but I still managed to get them soldered down. I found the LEDs to be the most challenging; figuring out the polarity was tough with the smaller sizes. The wheels finally fell off for me with the 0402s. I managed to get the resistor on, and the LED, but I must have reversed the polarity because the LED wouldn’t light. I tried unsoldering it and reversing it, but all I managed to do was turn it into a molten blob. I called it at 33 minutes, and Al generous scored me a 3.25 out of a possible 5.

How fast?

Records for the SMD Challenge have been falling all weekend. The winner last year put in an amazing 16 minute time. This year, Fred T. set the record with a mind-boggling time of 6:45! Contributing Editor Tom Nardi was watching that heat, and said, “The guy looked like he was just vibrating!” And the quality was top notch — it certainly looks hand-soldered rather than reflowed, but amazing nonetheless.

All in all, I really enjoyed taking the SMD Challenge. I learned a ton, and I feel like I added another skill to my repertoire. I’ve got several designs in the works that I was planning on making through-hole simply because I hadn’t taken the leap into SMD yet. Now that I have, I’ll have to rework the design and join the cool kids on the surface-mount side of the street.

November 18, 2019 at 07:01PM
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Used EDM Electrodes Repurposed as Air Bearings for Precision Machine Tools

Used EDM Electrodes Repurposed as Air Bearings for Precision Machine Tools
By Dan Maloney

If you’ve ever played air hockey, you know how the tiny jets of air shooting up from the pinholes in the playing surface reduce friction with the puck. But what if you turned that upside down? What if the puck had holes that shot the air downward? We’re not sure how the gameplay would be on such an inverse air hockey table, but [Dave Preiss] has made DIY air bearings from such a setup, and they’re pretty impressive.

Air bearings are often found in ultra-precision machine tools where nanometer-scale positioning is needed. Such gear is often breathtakingly expensive, but [Dave]’s version of the bearings used in these machines are surprisingly cheap. The working surfaces are made from slugs of porous graphite, originally used as electrodes for electrical discharge machining (EDM). The material is easily flattened with abrasives against a reference granite plate, after which it’s pressed into a 3D-printed plastic plenum. The plenum accepts a fitting for compressed air, which wends its way out the micron-sized pores in the graphite and supports the load on a thin cushion of air. In addition to puck-style planar bearings, [Dave] tried his hand at a rotary bearing, arguably more useful to precision machine tool builds. That proved to be a bit more challenging, but the video below shows that he was able to get it working pretty well.

We really enjoyed learning about air bearings from [Dave]’s experiments, and we look forward to seeing them put to use. Perhaps it will be in something like the micron-precision lathe we featured recently.

November 18, 2019 at 05:00PM
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Optical Keyboards Have Us Examining Typing at Light Speed-ish

Optical Keyboards Have Us Examining Typing at Light Speed-ish
By Bob Baddeley

There’s a newish development in the world of keyboards; the optical switch. It’s been around for a couple years in desktop keyboards, and recently became available on a laptop keyboard as well. These are not replacements for your standard $7 keyboard with rubber membrane switches intended for puttering around on your raspberry pi. Their goal is the gamer market.

The question, though, is are these the equivalent of Monster Cables for audiophiles: overpriced status symbols? Betteridge would be proud; the short answer is that no, there is a legitimate advantage, and for certain types of use, it makes a lot of sense.


Rubber dome switch for a membrane keyboard

We delved into this topic a bit before. Keyboards come in a variety of flavors, with the cheapest being membrane/rubber dome switches. These rely on a rubber dome that provides the spring force, and a small conductive pad on the underside of the dome makes contact with the PCB/membrane when pressed, connecting two traces. There’s no travel after the actuation; you press until the contact is made and you can press no further. Rubber dome switches are rated for about 5 million keystrokes.

Mechanical switches are the next step up. These have a spring that pushes the key up, and the key presses two metal strips together, but in such a way that contact is made before the travel is complete, so it’s possible to ride the key on the edge and press more rapidly. Of course, when writing a Hackaday article, this doesn’t matter, but when destroying your enemies with rapid fire in the comments section of a Hackaday article, it’s critical. These kinds of switches are rated for 20-50 million keystrokes. The keyboards are also known for their click-iness, and are popular at home and extremely unpopular in open offices.

animated switch
Switches can either make or break the beam when closed.

The shiny new thing is the optical switch. It is similar to the mechanical switch with the spring, but instead of having two metal contacts that touch, it has a piece of plastic that just moves up and down. On the PCB directly underneath is an IR LED and IR receiver. When the switch is pressed it breaks a beam and registers the keypress. By eliminating the metal components, they claim a lifespan of 100 million keystrokes.

There’s another technology called the optical analog switch, and as the name implies, it returns an analog value instead of a digital one, allowing you to measure the depth the key is pressed, and using it for turning a steering wheel or walking faster, or tuning the depth of stroke for a keypress register. Only a few keyboards have this, and some only have it on a few of the keys.

An Awful Lot of Keystrokes

A million keystrokes is a lot. People’s usage habits vary significantly, so it’s hard to say in hours or years how long the keyboard will last, but let’s just ballpark. If you rapid-fire a key 4 times a second, you’d have to do that for 347 hours to hit 5 million keystrokes and wear out your membrane keyboard. The King James Bible has 783,137 words, with a space after each one, so you’d have to type out the full thing more than 6 times before you wear out your space bar. In other words, 5 million is a LOT of keystrokes, but it’s not impossible. If you’re into games like osu!, though, you may be hitting the millions pretty quickly. If you’re curious about how long it’ll take you with your usage, try out WhatPulse to get your own statistics.

Speed Traps: From Debounce to the OS

Purveyors of the optical switch talk about switching at the speed of light.  Optical switches can be faster than mechanical switches because there’s no need for debounce. This can shave a few milliseconds off because most microcontrollers will wait for a bit to allow the contacts to settle before accepting that the switch has changed state to prevent multiple keypresses. The bigger impact is the keyboard’s scanning and processing speed, though. Keyboards have a microcontroller that doesn’t have an input for every key. Instead it uses multiplexing and scans through each key rapidly. If it’s taking a long time to scan the matrix because it only has a few GPIO and must multiplex a bunch of things, then it may take longer to process the keys pressed. A cheap membrane keyboard won’t have the better microcontroller found on gaming keyboards.

The keyboard processor might not be the greatest source of latency, either. USB 2.0 has a max polling rate of 1000Hz, but for most keyboards that use low-speed USB, that polling frequency is 125Hz, or 8ms delay. Then of course there’s the delay by the operating system and the application handling the keyboard inputs, plus the timing involved with the display and rendering the output or the thing causing the reaction keystroke. On games where rhythm matters, it’s common to have configuration options that are adjusted to synchronize the audio, video, and input, eliminating the latency of the system as a problem.

Another option is to use a USB to PS/2 adapter, which some keyboards support. Since PS/2 is interrupt driven, it can be faster than the 125Hz polling of USB, but fewer and fewer motherboards have PS/2 options, and it’s not a guarantee that it will be faster.

For anyone using a keyboard for writing, speed doesn’t matter. Any keyboard would be more than capable of handling the fastest typists. For people looking to maximize their edge in games of speed and accuracy, where tuning equipment down to the millisecond matters, then mechanical keyboards have an edge, and optical keyboards have an even greater edge.

However, for the gamers who play speed-clicking games, an optical keypad with only a few keys is a much smaller and cheaper option with all of the speed benefits.


disassembled membrane keyboard
The rubber sheet covers three plastic layers. Two have metal traces deposited, and an inner layer acts as a separator.

We know how rubber dome membrane keyboards fail. They are pretty robust and tolerant of liquids and dirt. When they fail it’s because the rubber has suffered fatigue and cracked or gotten “mushy” and lost its spring. Sadly because the whole keyboard is a single piece, replacement of an individual switch is difficult, but because of its simplicity it’s pretty easy to keep clean.

Mechanical keyboards fail, too, usually because the metal contacts become corroded. While it’s possible to replace the individual keys, that typically requires desoldering the defective ones. But at least it can be done, and the whole keyboard doesn’t have to be scrapped because of a single fault.

The big unknown here is non-mechanical component failure. With optical keys, no mechanical contact means one less failure point. Further, the keys can be replaced entirely, without soldering, making repair much more accessible. However, if the failure is of the electronics themselves, then the board is destroyed, and we know that IR LEDs fade, or get covered by debris, or are damaged through a spill. Assuming that an IR LED will fade to 50% brightness and start to cause detection problems after 50,000 hours, that’s 10 years at 12 hours/day (the LED has to be on, whether the key is pressed or not). Less if it’s driven outside of spec. Yes, it’s a long time, but the point is that optical keyboards won’t last forever.


Rubber dome switches, and their related cousin the scissor switch, which is more common for laptops and thin portable keyboards, have a similar feel. They don’t press until the end of their travel, they all have similar sounds, and the force is pretty much the same. Mechanical keyboards offer a wide variety of options, including loudness, actuation force, and travel distance. Optical switches are designed similar to the mechanical ones with an equivalent range of features. This is purely a matter of personal taste.


Make your own keypad to try it out.

Membrane keyboards are cheap, and effort is made to only include features that are cheap. That’s why they don’t have an RGB under every keycap. However, the switches themselves don’t add much to the cost of the unit, so membrane keyboards are usually full keyboards with numpads and media keys. Optical and mechanical keyboard switches are expensive for each key, so they often have fewer keys, but make up for it with bright configurable patterns underneath. The analog optical keyboards have many more features, including the ability to set multiple actions for a single key based on distance pressed, or have adjustable press distance.


Like any other sport or hobby, the vast majority are served well by basic gear. For those in the upper levels of performance, or those who just want to own the best of the best, there exists a whole category of computer equipment. Get a mechanical keyboard if you like the feeling of the switches. Get an optical keyboard if you’re a hardcore gamer who needs every millisecond of reaction time and operate at the highest levels of gaming. There’s definitely a difference, and the math and experiments bear that out. Be prepared to spend some time tuning, though, as there are a lot of steps on the path from the finger to the screen. For everybody else, though, cheap keyboards are a great deal that last a really long time and have performance that meets most needs. Of course, you could always make your own rubber dome keyboard, mechanical keyboard, or tiny keyboard.

November 18, 2019 at 04:01PM
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Add A Bit Of PCB Badge Glamour To Your Boring ID Badge

Add A Bit Of PCB Badge Glamour To Your Boring ID Badge
By Jenny List

When we talk about badges and printed circuit boards, it is usually in the context of the infinite creativity of the Badgelife scene, our community’s own art form of electronic conference badges. It’s easy to forget when homing in on those badges that there are other types of badge, and thus [Saimon]’s PCB badge holder is an entertaining deviation from our norm. His workplace requires employees to carry their credit-card-sized ID pass with them at all times, but the plastic holder that came with his had broken. So he did what any self-respecting engineer would do, and designed his own holder using PCBs.

It’s a three-way sandwich with identical front and back PCBs featuring a nice design, but the clever bit is the middle PCB. It is U-shaped to slide the card in from the side, but to retain the card it has a couple of springy milled PCB arms each with a small retaining tooth on the end. This is an ingenious solution, with just enough give to bend, but not so much as to break.

The three boards are glued together, it seems his original aim was to reflow solder them but this was not successful. The result is an attractive and functional badge holder, which if Hackaday required us to have a corporate ID you can be sure we’d be eyeing up for ourselves.

November 18, 2019 at 01:00PM
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SiCK Mechanical Keyboard is 3D Printed

SiCK Mechanical Keyboard is 3D Printed
By Al Williams

We’ve noticed a rash of builds of [ FedorSosnin’s] do-it-yourself 3D-printed mechanical keyboard, SiCK-68 lately. The cost is pretty low — SiCK stands for Super, Inexpensive, Cheap, Keyboard. According to the bill of materials, the original cost about $50. Of course, that doesn’t include the cost of the 3D printer and soldering gear, but who doesn’t have all that already?

The brains behind this is a Teensy that scans the hand-wired key matrix. So the only electronics here are the switches, each with a companion diode, and the Teensy. The EasyAVR software does all the logical work both as firmware and a configuration GUI.

If you look at the many different builds, each has its own character. Yet they look overwhelmingly professional — like something you might buy at a store. This is the kind of project that would have been extremely difficult to pull off a decade ago. You could build the keyboard, of course, but making it look like a finished product was beyond most of us unless we were willing to make enough copies to justify having special tooling made to mold the cases.

PCBs are cheap now and we might be tempted to use one here. There are quite a few methods for using a 3D printer to create a board, so that would be another option. The hand wiring seems like it would be a drag, although manageable. If you need wiring inspiration, we can help.

For ultimate geek cred, combine this with Ploopy.

November 18, 2019 at 10:00AM
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Building a 3D Scanner with a 3D Printer

Building a 3D Scanner with a 3D Printer
By Bryan Cockfield

Using a 3D printer to make high quality parts is a great way to improve the look and appeal of any project. If you want to replicate something exactly, though, you’ll need either a very good set of calipers and a lot of time or a 3D scanner. Using the 3D scanner and the 3D printer go along very well together, especially if you use your 3D printer to build your 3D scanner too.

This project comes to us from [Vojislav] who spent the past two years perfecting this 3D scanner. Using a vast array of 3D printed parts, this build looks professional on every level. It also boasts a Raspberry Pi Zero and a fleet of camera modules, not to mention its own LED lighting. [Vojislav] has provided the printer files and the software needed to run it on the project page. It all runs through command line and python code, but that shouldn’t be a big hurdle.

While there is no video of it in action, it seems like all the parts are there for a solid 3D scanner, provided you have access to a 3D printer that can churn out the parts you’ll need. If you need something larger, there are some other options available as well that really take your photogrammetry skills to the next level.

November 18, 2019 at 07:00AM
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Rotary Dial Becomes USB Keyboard

Rotary Dial Becomes USB Keyboard
By Al Williams

[Max] had a rotary dial from an old telephone and — unsurprisingly — had nothing in particular to do with it. The simple answer? Use an Arduino Leonardo to turn it into a USB keyboard device.

Of course, the Leonardo can easily impersonate a USB keyboard, so that’s the easy part of the project. Interfacing to the dial requires an understanding of how the phone system works.

While today, TouchTone phones are most common, they were quite uncommon for many years. Early phones required you to have an operator connect your circuit to another person’s circuit. Unfortunately for the operators, the system was inherently unscalable and also cost prohibitive.

There were a variety of schemes tried and — supposedly — an undertaker who was angry that the operator was connecting his customers to her husband’s competing mortuary invented the dial telephone.

The details are pretty simple. A typical dial has two contacts. There’s a normally open contact that closes when you spin the dial to any position. It says closed until the spring returns the dial to the home position.

The other contact is normally closed and makes or breaks the phone line. Each time the dial rewinds past a position, the contact opens briefly. Of course, this is a mechanical system, so the software has to debounce the inputs, but that’s easy enough.

If you don’t have access to a dial, you could always print one. Sort of.

November 18, 2019 at 04:00AM
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