Micro-Sized Flex For Commercial Quality Bodging

We love watching the creativity unleashed by the democratization of once-exotic technologies. The casualness by which one can order a cheap, small run of PCBs has unlocked a flood of fine pitch components and projects which look commercial quality even with a total build volume of one. Now the once mythical flex PCB has been falling from it’s stratospheric pricing and with OSHPark’s offering it feels like we’re at the inflection point. [qwertymodo] leveraged this by creating a beautifully twisted flex to add link port support to the Super Game Boy

In the mid-90’s Nintendo released the Super Game Boy, a cartridge for the SNES which allowed you to play Game Boy games on the big screen. Each cartridge was in fact an entire Game Boy with the appropriate hardware to present it in a way the host console could interface with, but missing some of the hardware a standalone Game Boy would include like a link port to connect it to another system. This mod fixes this limitation by bridging the correct pins out from the CPU to a breakout board which includes the link port connector. For general background on what’s going on here, check out [Brian]’s article from April describing a different mod [qwertymodo] executed to the same system.

What’s fascinating is how elegant the mod is. Using a a flex here to create a completely custom, strangely shaped, one-of-a-kind adapter for this random IC, in low volume is an awesome example of the use of advanced manufacturing techniques to take our hacks to the next level. It reminds us a little of the method [Scotty] used to add the headphone jack to his iPhone 7 back in 2017. At the time that seemed like a technology only available to hackers who could speak a little Mandarin and lived in Shenzhen.

Detailed information on this hack is a little spread out. There is slightly more info in these tweets, and if you have a Super Game Boy crying out for a link port the adapter flexes are sometimes available here. Look beyond the break to see what the mod originally looked like sans-flex.

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A New KiCAD Tutorial Hits The Scene

KiCAD has a rightfully earned image problem regarding beginners. The shiny new version 5 has improved things (and we’re very excited for v6!) but the tool is a bit obtuse even when coming from a electronics design background, so we’re always excited to see new learning material. [Mike Watts] is the latest to join the esteemed group of people willing to export their knowledge with his KiCAD tutorial series on GitHub that takes the aspiring user from schematic through fab and assembly.

The tutorial is focused around the process of creating a development board for the dimuitive Microchip née Atmel ATSAMD10 Cortex M0 ARM CPU. It opens by asking the reader to create a schematic and proceeds to teach by directing them to perform certain actions then explaining what’s going on and which shortcuts can accelerate things. This method continues through layout, manufacturing, and assembly.

Of note is that when defining the board outline [Mike] describes how to use OpenSCAD to parametrically define it; a neat micro-tutorial on using the two great tools to compliment each other. We also love that upon successful completion of the tutorial series the user will have developed a tiny but useful development board that can be assembled for about $3 in single quantities!

As with all open source work, if you have quibbles or want to contribute open a pull request and give [Mike] a hand!

High Precision Analog IO With Digital Pins

Reading the temperature of your environment is pretty easy right? A quick search suggests the utterly ubiquitous DHT11, which speaks a well documented protocol and has libraries for every conceivable microcontroller and platform. Plug that into your Arduino and boom, temperature (and humidity!) readings. But the simple solution doesn’t hit every need, sometimes things need to get more esoteric.

The technique summarized by an image from Microchip Appnote AN685

For years we’ve been watching [Edward]’s heroic efforts to build accessible underwater sensing hardware. When we last heard from him he was working on improving the accuracy of his Arduino’s measurements of the humble NTC thermistor. Now the goal is the same but he has an even more surprising plan, throw the ADC out entirely and sample an analog thermistor using digital IO. It’s actually a pretty simple trick based on an intuitive observation, that microcontrollers are better at measuring time than voltage. 

The basic circuit

The circuit has a minimum of four components: a reference resistor, the thermistor, and a small capacitor with discharge resistor. To sense you configure a timer to count, and an edge interrupt to capture the value in the timer when its input toggles. One sensing cycle consists of discharging the cap through the discharge resistor, enabling the timer and interrupt, then charging it through the value to measure. The value captured from the timer will be correlated to how long it took the cap to charge above the logic-high threshold when the interrupt triggers. By comparing the time to charge through the reference against the time to charge through the thermistor you can calculate their relative resistance. And by performing a few calibration cycles at different temperatures ([Edward] suggests at least 10 degrees apart) you can anchor the measurement system to real temperature.

For all the gory details, including tips for how to save every last joule of energy, check out [Edward]’s post and the Microchip appnote AN685 he references. Besides this series [Edward]’s Cave Pearl Project has already yielded an impressive number of Hackday posts. For more great hardware writeups check out a general hardware build for a single sensing node, or the “temperature sensor” [Edward] made with no external parts at all!

An Epic Tale Of Thermistors: Tricks For Much Better Temperature Sensing

For years [Edward] has been building professional grade underwater sensing nodes at prices approachable for an interested individual without a government grant. An important component of these is temperature, and he has been on a quest to get the highest accuracy temperature readings from whatever parts hit that sweet optimum between cost and complexity. First there were traditional temperature sensor ICs, but after deploying numerous nodes [Edward] was running into the limit of their accuracy. Could he use clever code and circuitry to get better results? The short answer is yes, but the long answer is a many part series of posts starting in 2016 detailing [Edward]’s exploration to get there.

Orange is 12 bits, red is 24

The first step is a thermistor, a conceptually simple device: resistance varies with temperature (seriously, how much more simple can a sensor get?). You can measure them by tapping the center of a voltage divider the same way you’d measure any other resistance, but [Edward] had discarded this idea because the naive approach combined with his Arduino’s 10 bit ADC yielded resolution too poor to be worthwhile for his needs. But by using the right analog reference voltage and adjusting the voltage divider he could get a 20x improvement in resolution, down to 0.05°C in the relevant temperature range. This and more is the subject of the first post.

What comes next? Oversampling. Apparently fueled by a project featured on Hackaday back in 2015 [Edward] embarked on a journey to applying it to his thermistor problem. To quote [Edward] directly, to get “n extra bits of resolution, you need to read the ADC four to the power of n times”. Three bits gives about an order of magnitude better resolution. This effectively lets you resolve signals smaller than a single sample but only if there is some jitter in the signal you’re measuring. Reading the same analog line with no perturbation gives no benefit. The rest of the post deals with the process of artificially perturbing the signal, which turns out to be significantly complex, but the result is roughly 16 bit accuracy from a 10 bit ADC!

What’s the upside? High quality sensor readings from a few passives and a cheap Arduino. If that’s your jam check out this excellent series when designing your next sensing project!

Visualizing LEDs For More Efficient Pin Packing

The archetypal “blink an LED” is a great starter project on any platform, but once the bug takes hold that quickly turns into an exploration of exactly how many LEDs a given microcontroller can drive. And that often leads to Charlieplexing. A quick search yields many copies of The Table describing how many LEDs can be driven by a given number of pins but that’s just the most rudimentary way to describe it. Way back in 2013 [M Rule] developed a clever trick to describe the number of LED matrices which can be driven by a Charlieplexed array of a given size that makes this process much more intuitive. The post may be old, but we promise the method is still fresh.

[M Rule] was specifically looking to drive those big, cheap single color LED matrices which are often used to make scrolling signs and the like. These parts are typically a matrix of LEDs with a row of common cathodes and one of common anodes. Internally they are completely dumb and can be driven by row/column scanning, or any other way a typical matrix can be controlled. The question is, given known matrix sizes, how many can be driven with a a number of Charlieplexed LED drive pins?

The first step is to visualize the 1D array of available pins as a 2D matrix, as seen to the right. Note each numbered pin is the same on the X and Y, thus the black exclusion zone of illegal drive pin combinations slicing across the graph (you can’t drive an LED connected to one pin twice). The trick, if one were to say it resides in a single place, would be titling the axis anode and cathode, representing two “orientations” the drive pins can be put in. With this diagram [M Rule] observed you can simply drop a matrix into the array. If it fits outside the exclusion zone, it can be driven by those pins!

To the left is what this looks like with two 8×8 matrices, one connected between pins 1-8 and 9-16, the other connected between 9-16 and 1-8. This isn’t terribly interesting, but the technique works just as well with single LEDs and any size matrix, including 7-segment displays. Plus as long as an element doesn’t overlap itself it can wrap around the edges leading to some wild visuals, like 14 RGB LEDs on seven pins to the right.

The most extreme examples are pretty exotic. Check out [M Rule]’s post for the crown jewel; 18 pins to drive six 5×7 modules, six 7-segment displays, 12 single LEDs, and 18 buttons!

If this color coded diagram seems familiar, you may be remembering [openmusiclabs]’ excellent diagram describing ways to scan many of buttons. Or our coverage of another trick of matrix topology by [M Rule] from a few weeks ago.

Homemade Magic Makes The Metcal Go

First soldering irons are often of the Radioshack or Maplin firestarter variety. They’re basically wall power shorted across a nichrome heater or similar with some inline resistance to make it harder to burn down the house. You plug them in, the current flows, and they get hot. Done.

If you stick with the hobby for a while, these eventually get replaced with something like the venerable HAKKO FX-888D or that one Weller everyone likes with the analog knob. These are much improved; having temperature control leads to a more consistently heated tip and much improved soldering experience.

Entering the electronics workplace one comes across the next level of quality soldering iron: high end HAKKOs, Metcals, JBCs, and the like. Using one of these irons is practically a religious experience; they heat in a flash and solder melts while you blink. They even turn off when you put the handpiece down! But they’re expensive to buy (hint: think used). What’s a hobbyist to do?

[SergeyMax] seems to have had this problem. He bit the bullet, figured out how the Metcal works, and made his own base. This is no mean feat as a Metcal might look like a regular iron but it’s significantly more complex than ye olde firestarter. The Metcal magic is based on a oscillating magnetic fields (notice the handpiece is connected via BNC?) interacting with a tip bearing a special coating. In the presence of the changing field the tip heats up until it hits its Curie temperature, at which point it stops interacting with the magnetic field and thus stops heating.

When the user solders, the tip cools by sinking its heat into the part and drops below the Curie temperature again, which starts the heating again. It’s like temperature control with the sensor placed absolutely as close to the part as possible and a nearly instant response time, without even a control loop! [SergeyMax] has a much more thorough description of how these irons work, which we definitely recommend reading.

So what’s the hack? Based on old schematics and some clever reverse engineering from photos [SergeyMax] built a new base station! The published schematic is as rich with capacitors and inductors as one could hope. He didn’t post source or fab files but we suspect the schematic and photos of the bare board combined with some tinkering are enough for the enterprising hacker to replicate.

The post contains a very thorough description of the reverse engineering process and related concerns in designing a cost efficient version of the RF circuitry. Hopefully this isn’t the last Metcal replacement build we see! Video “walkthrough” after the break.

Edit: I may have missed it, but eagle eyed commentor [Florian Maunier] noticed that [SergeyMax] posted the sources to this hack on GitHub!

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Tokyo Mechanical Keyboard Meetup Knocks Our Clacks Off

Just a few days ago, on the other side of the planet from this author, there was a mechanical keyboard meetup in Tokyo. Fortunately through the magic of the Internet we can all enjoy the impressive collection of devices people brought, and boy were there some interesting specimens. There were certainly the inevitable collections of strange artisan keycaps, unusual handmade switches, and keycap sets only available in one group buy five years ago in Nicaragua. But among the bright colors were some truly unique custom designs the likes of which we haven’t see before. A single source is hard to credit, you could check the hashtag #tokyomk6 on Twitter, or [obra]’s thread of photos, or this great blog post (video walkthroughs and photos included) from [romly].

Speaking of [romly], one of their designs stands out as particularly unusual. There are a few things to note here. One is the very conspicuous surface profile of the (clearly totally custom) keycaps themselves. Instead of flat or cylindrical or spherical, these are round. Round like the outside of a log. If we didn’t know better it might look like the entire thing was sculpted or extruded as a single unit. And just below the deck are the perpendicular thumb clusters. Frankly we aren’t sure how to refer to this design feature. The switches are mounted at right angles facing inward so the user places a thumb inside it in a style reminiscent of the DataHand. It’s quite interesting, and we’d be love to know more about what specific functionality it provides.

Another interesting entrant is this keyboard with unusually staggered switches and hexagonal caps (check out the individual markings!). Very broadly there are two typical keyboard layout styles; the diagonal columns of QWERTY (derived from a typewriter in the 1800’s) or the non slanted columns of an “ortholinear” or matrix style layout. By those metrics this is something like an ortholinear keyboard in that its switches overlap their neighbors by half, but the edge to edge close packed caps imply that it might be something else.  We’d be very interested to know how typing on this beast would be!

There were so many more awesome designs present at the meetup that this would never end if we tried to document them all. Take a look through the posts and call out anything else too excellent to go unnoticed!

Thanks [obra] for Tweeting about this so we could discover it.