# Demilight v 0.9.1

The Demilight (miniature moving light) project has been slowed down in the past few months, mostly by good things. Namely, my return to my fulltime job and other interesting technical nerdery. But the project soldiers on!

I made a video detailing the trials and tribulations of getting version 0.9.1 built, which you can watch below (embedded) or over on YouTube.

# Video: Demilight Version 0.8

It’s been quite awhile since the mini-moving light project (now renamed The Demilight) has been written up on the blog. The project was in hiatus for a few months while dove into the technical challenges of a new job, but as the job isn’t keeping quite as busy at the moment (here in early summer 2020), it’s back on the workbench. I’ve put together a video showcasing the current state of the project, now in version 0.8:

The video does a pretty decent job of capturing the current state of things. So what’s next?

Firstly, the goofs I alluded to in the video that I consider to be must-fix items before the files are ready for primetime. Theu mostly have to do with the 3D-printed parts – I adjusted the access holes and programming slots from version 0.5 to 0.8, but I didn’t do a great job double-checking everything, and things don’t line up very well. That’ll need another few test prints and some adjustment to alleviate the all the filing that’s currently necessary.

I’ve also been having some issues with mechanical assembly – I’ve been using some M2 insert nuts to hold the case and case-lid together, and to secure the PCB into the case, but that doesn’t seem to be a particularly good system. It’s possibly my nuts and bolts are just really high-tolerance, but they’re constantly cross-threading and not inserting all the way. I think a more robust solution is in order.

The other main error has to do with the footprint for the 5V buck-converter module – somehow, my pin placement is off by .2″ on the PCB footprint, which makes the part overlap with the attachment points for the servos unless you bend the voltage-regulator’s pins over. Not insurmountable, but really annoying. That’ll have to get fixed in version 0.9. Once those two most-egregious errors are corrected, though, I think the unit will be decent enough to publish as a beta version.

It’s a pretty simple part… how did I goof this up?

There are several more substantial improvements in the pipeline as well. In no particular order:

As I mention in the video, I’m working on a miniaturized programmer interface based on some little 0.05″-pitch pogo pins. The results, so far, have been mixed – I have been able to confirm that the interface is providing gnd/5V to the ATmega328, at least enough that its 16 MHz ceramic resonator is oscillating, but I can’t seem to program the chips in-place. Further experiments will be necessary.

Some iterations of the Demilight have incorporated a heatsink to help manage the heat-output from the LED emitter chips. To be honest, I’m not sure how necessary it is – I would love to set up some tests with the unit running at its full 1 Amp current and see just how hot things get. Perhaps the first test would be in free-air, then inside the case in multiple orientations. I know from some tests I did on a livestream last summer that with enough heatsinking the LED stars can handle up to about 5 Amps, but they dump a huge amount of heat at the point.

If the heatsink comes back, should it still be in candy-apple red?

RGB or RGBW dimming capacity would be really neat – as spiffy as the pure-white versions are, there’s something about color-changing light that feels like it would take this project to the next level. I would need to free up some more PCB space, and possibly move from a single-channel driver to a 3 or 4 channel driver, but finding those in the ~1A current capacity range seems a little tricky.

There are also a couple of purely aesthetic things which could get bumped up to something better. I’ve ordered some 1/4″ white wire sleeving to take the place of the gaff tape covering the wires that run from head to base. And I need to invest a little time dialing in my 3D printer – after 3.5 years of printing, it’s starting to show its age a little bit, and a little extra tightening and lubrication wouldn’t be a bad idea.

So many of my projects during quarantine have focused on building my digital communication mediums – building out this video feels very much like a continuation of that skill-building. The weekly Arduino/Electronics classes I’ve been teaching for 15 weeks now have been a serious crash course in live digital video. That learning process deserves a write-up of it’s own, but if you compare the following two frames from Episode 0 (testing) and Episode 14 (Wireless Signals), I think the improvements are pretty clear:

Epsiode one was…. pretty rough. The audio is really crunchy too – turns out I had two microphones on (lav and webcam) and they did unkind things together.

We’ve got things pretty well dialed in by now.

It’s been a joy to build some more digital video skills putting this video together, like putting together a basic script, recording a voiceover, learning the editting, effects, and color-grading processes… it’s been both fascinating and time-consuming. The video definitely has some rough edges, but I’m thinking of it as good-enough, and I’m excited to take what I’ve learned from this early creation and apply it to future videos. Much like the tiny-light itself, it’s good to just make a thing, anything, a small thing, and iterate from there.

# Geared Nameplate

A quickie today – over the weekend, I decided that my workshop at work needed a nameplate outside the door, to make it a little easier for folks to find me. So I put together this design in Fusion 360, and printed it in black and white PLA+. (The “grey” of the gears is a single later of white PLA on top of black gears).

The gears have 8, 9, 10, 12, 14, and 16 teeth, and are symmetrical left/right. This means that it takes 630 revolutions of the smallest gear to return the arrangement to its starting place. We determine this by finding the least common multiple of the number of teeth, which is $2^4 * 3^2 * 5 * 7$ or 5040. Divide that by the 8 teeth on the smallest gear, and we get our 630 revolutions to return to where we started.

The design has two chamferred holes for screw-mounting, but it’s currently just stuck on the wall with sticky-tack.

# Setting up an Electronics Lab – Tools

Between 10 years working in stage lighting, live video, and theatrical special effects; three moves and two home workbench-overhauls; and my new-this-month position as an Exhibit Engineer at a major Midwest science museum, I’ve planned and kitted-out many electronics workbenches over the years. For those interested in getting involved in hobby or professional electronics work, I’ve compiled the tools I think are most useful when building up a workspace for electronics construction and troubleshooting.

I’m going to specifically focus on tools and support-hardware this time around, and not dive too deep into supplies and consumables, purely to maintain focus. The parts and pieces you need will be wildly different if your specific focus is scratch-building accelerometers vs twitter-connected instant cameras, say. But in the wide and deep pool of ‘working with electronics,’ here are some flotation aids that will keep your head above water most of the time.

### Soldering

As both hobbyists and professionals, we are often looking not for the best tool, but one that’s good enough for the job without breaking the bank. If there’s one tool that I’d recommend getting the ‘good’ versus the ‘good enough’ version, it’s a soldering iron. I thought for years I was just bad at soldering. Nope, just a crappy \$25 Radio Shack soldering iron that was doing me no favors.

Not that ‘good’ has to mean ‘super expensive.’ In my home shop and my current shop at work, I used the Hakko 888D, which has proved reliable and durable, even if the interface is a little unintuitive. For less than \$100, that’s a darn good iron. The shop at my previous job has a cheapie 3-in-1 soldering/hot-air-rework/power supply station, and for most things that was just fine. They’re such a huge leap above a ‘soldering pencil,’ and they’ll last for years,

The trust Hakko 888D. I now have one of these at home and one at work, and they’re a very nice little iron.

Whatever iron you choose, you’ll want some additional tips to go with it. While you could get the pack of every tip imaginable, I find myself using either the medium chisel or the fine-conical %99.9 of the time, so a smaller assortment is probably fine.

As far as solder, while there are good environmental reasons to go with lead-free solder, there’s nothing quite so good to work with as classic Kester rosin-core 60/40, nice and thin. A one-pound reel of that stuff will last most people years. While you could buy a solder-reel stand, I’ve found a 3D-printed design that I really like (credit to Phredie on Thingiverse).

One pound of Kester 60/40 in my favorite 3D printed holder. As busy as we are, I might actually make in through this roll in a year or two.

You’ll also want some flux, either as a paste or in my preferred form as a solder pen. While rosin-core solder has flux built-in, any time you’re doing rework, SMD work, or just taking a little longer to deal with a tricky part, flux makes sure your surfaces are clean and ready to accept the molten solder.

Speaking of keeping things clean, let’s talk about cleaning your soldering iron tip. The sponge and wire-wool cleaner than come with your iron are plenty, if you treat your iron right. More aggressive chemical fluxes like those found in “tip-tinners and cleaner” are meant to remove long-built-up oxidation on your iron tip, and are overkill for routine tip-cleaning. I was taught to dab the iron in the wire-wool between each joint (realistically, between every several joints), and wipe on the sponge before the iron goes back in the stand. That should be all you need.

To remove solder from things other than your iron may take some special tools. De-soldering braid is a great tool – its a woven copper ribbon impregnated with flux, that, when heated against a solder joint, sucks the molten solder up via capilary action. For getting the last little bit of solder out of through-hole pads, a solder-sucker is the tool – find yourself a cheap one, they’re all pretty much the same. At my last job, we purchased a cheap vacuum desoldering station, which was fine, but mostly could have been replaced by solder-wick in 90% of applications. Perhaps a brand-name vacuum desoldering station would have done the job better, but in any case when setting up my shop at the new job, I passed on this tool. For more thoughts on all these tools/techniques, W2AEW has a great video on desoldering if you find yourself in a pinch.

Whether your soldering or desoldering, you’re going to be making some nasty fumes melting all that flux, so get yourself some kind of filtering fan. I’ve got a dirt-cheap Aoyue filter-fan on my home bench, and both a cheap Kotto and an expensive Hakko on my bench at work now, and they’re all about as good as each other, and they all suck (not in the way you want a filter fan to suck). I replaced the fan in my Aoyue with a 120V 4″ Muffin fan (pulled from an closing musical’s fog-distribution system, in my case), and it’s made a world of difference, I highly recommend upgrading. Just be careful, those fans bite.

Now that’s a big fan! Inherited from a previous museum exhibit.

There are about as many different kinds of work-holding clamps as there are people who solder, but my two favorites are this 3D-printed PCB vise for flat-work and these octopus-style 3rd-hands for other unusual shapes. I’ve used the classic Panavise clamps, and for a shared-shop environment I’d recommend them for their sturdy build quality. But I find them to be a little bit too bulky and their jaws not quite wide enough for the work I find myself doing, so I opt for other solutions in my just-for-me setups. You do you though.

Almost 6″ of jaw space on this 3D printed workholder. You can tell I ran out of grey filament halfway through printing the parts.

### Electronic Test and Measurement

The two big items in this category are multimeters and oscilloscopes. Let’s take a look at both of them first before we get into some more specialized tools.

There are lots and lots of good-enough multimeters in the world today, of all kinds of different brands, and they’re pretty much going to all be OK. Rather than try and pick out specific ones from Amazon, here are the features I’d look for if I was looking to add a decent multimeter to my bench today:

• The basics: AC/DC Voltage, AC/DC Current (up to 10A is useful), resistance (to 0.1Ω and 1 MΩ is nice).
• Continuity test- this is the most useful setting on a multimeter. Using this setting and touching a wire/component/circuit with the probes will tell you if there’s a low impedance path between the two points; i.e., if they’re connected. Super useful.
• Auto power-off. Doesn’t seem like much, but it’s real easy to kill batteries without it.
• 4-digit precision (some cheap meters only give 3)

The other features a meter might have include: temperature measurement, diode-forward-voltage measurement, True RMS AC measurement, frequency (power line), duty-cycle, capacitance, transistor hFE, illumination… the list goes on. I’ve appreciated having a true RMS measurement in tricky AC power situations, and having an easy frequency-check can be handy, but for the rest of these, I’d rather rely on a purpose-made tool like a thermometer, lightmeter, or transistor checker, rather than something built into my multimeter.

I got this meter almost 8 years ago in a moment of need, at a Menards if memory serves, and it’s worked swell ever since.

If you’ve got the cash and are looking for something to last 20 years, the Fluke 117 is a really solid primary meter. Fluke has been the brand name in quality meters for the past lots-of-years – well made, reliable, accurate. Not super cheap, but you do get what you pay for. My current department has standardized on them, and that’s been swell. For most things, we don’t need the \$300+ meter (which gives you min/max tracking and microAmp measurement) or the \$500 meter (with its fancy clamps and probes). In fact, a basic \$40 meter is going to be fine for almost everything you do.

A little aside – why are there no benchtop-multimeters in the super-affordable price range? When you can get a passable, portable multimeter for \$20, why are even the cheapie-versions of a benchtop meter still \$150? I think there would be a strong market for a \$60, benchtop form-factor, ok-ish meter. I have an old Simpson 460-6 at work that I love using, not because it’s the world’s most amazing meter, but just because it’s always there and the form factor is right. How about it, AliExpress?

Now can I get this form factor, with a little adorable LED display, for less than \$200?

Moving on to oscilloscopes, I think there are some who would say they aren’t essential for electronics work – after all, if you end up working mostly with digital signals, or analog-voltages that don’t change over time, is it really worth it? I would counter that the oscilloscope is your eyes into the realm of what your electronics are doing, and is a vitally useful tool in many situations. If you’ve never used an oscilloscope, may I once again recommend a video by W2AEW.

Scopes are another arena where you don’t need to break the bank to get something decent enough to use. My first scope was a well-aged BK-Precision 1535A 35Mhz analog scope that a bought from a guy on Craigslist for about \$40. For basic electronics work, 20Mhz or so is plenty – you’re most likely going to working at slower speeds (audio to 20Khz, maybe 250kHz for serial or RS485) or much, much higher (HDMI, USB, etc) where a scope really isn’t the right tool in most cases anyway. Or at least, once you’ve progressed to the level where you’re worrying about measuring GHz signals, you’ve likely acquired more specialized tooling along the way.

This old thing is still puttering away on my workbench. Still worked just fine for most things I’d care to do with it.

I think a decent analog scope is a really good place to start if you’ve never used a scope before – better to tackle the fundamentals of the tool before having to learn how to use a particular menu structure as well. The shop at my new job came with a Hitachi V1565 100MHz analog scope with measurement capability that I’ve been very happy with – the ability to add cursors to an analog display to measure voltage, time, or duty cycle is handy. At home I’ve now also got an Owon PDS5022T 25MHz digital scope that was gifted to me – I like the tools having a digital scope provides, but I find it significantly more clunky than either of the classic analog scopes in my life.

The “new” (to me) oscilloscpe I have at work. 100MHz bandwidth is overkill for anything I can think we’ll run into, but you never know…

So, if you’re looking for a bench scope and you’ve never used one before, I’d say start analog. I see on eBay right now you can buy a gently-loved 2-channel analog scope for around \$50-60 (plus \$40 shipping, those things aren’t light). Not a bad way to go.

Something my accomplice at my old job turned me on to is small, portable oscilloscopes. I don’t have a specific model to recommend, but they can be useful in specific circumstances – not so much to actually interrogate the characteristics of a signal, but more as a signal checker. Do I have AC here, do I have something that looks like RS-485 there, etc? If you do buy one, make sure you get one with an integrated battery (not all do) – getting one that still has to be plugged in makes it far less useful.

There are some more niche electronic tools that I make use of on my bench, but mostly because of my ham radio background. A decent frequency counter is useful in that arena – I’ve got a classic Heathkit IM-2420 that I picked up at a swap-meet, but I’m really intrigued by the new wave of inexpensive benchtop frequency counters that have popped up in the past couple years that claim to do 0.1Hz-2.4GHz for only \$70. A signal genetor is also really useful in my work – I built my own around an Si5351 and an Arduino, but you can buy a 0-25Mhz or 0-60Mhz arbitrary function generator for not a lot of cash these days, and I have colleagues who speak highly of both. Since my last job was more lighting-focused, we purchased an Extech digital lightmeter for a specific project – sometime I’d love to get into why that specific meter and the challenges of metering LED sources, but that discussion is too long for this margin to contain.

Some specialized tools for specialized circumstances. A sweep generator, frequency counter, DC power supply, oscilloscope, and homebrew frequency generator.

### Electrical Power

A source of consistant, controlled DC power is vital for electronics work, since most projects are going to be some flavor of DC-powered. For basic logic-level type work, the least-expensive option is probably an ATX computer power supply with an ATX breakout board, which will at least provide +3.3, +5, +12 and -12V, which suffices for a lot of Arduino+sensors or Raspberry Pi+breakouts type projects. There are a thousand flavors of those breakout boards, so make sure you find one with the ATX connector type that matches your power supply. There are also screw terminal and terminal lug versions, if you have strong feelings either way.

If your work is less module-oriented and more about building up circuits in a more from-scratch way, a current-limited bench power supply is key. A decent power supply will supply relatively low-ripple DC voltage from 0 to 20 or 30 or 50 volts, at 5 or 10 amps max, commonly. What’s more, you can set a current-limit such that, when your project runs away and tries to turn itself into a pile of smoke, at least it does so more slowly – the power supply will typically fold back its output voltage to keep the output current below the value you specify. Some fancier models also have the option to just cut off current entirely until the power supply is reset.

Versions of this Yescom power supply are available all over the internet at around the \$50 price point.

My current recommended inexpensive bench power supply is the Hanmatek HM305P, for a couple reasons – having a digital display so you can set the output voltage at, say, exactly 5V, is handy. As are the six front-panel preset buttons that allow you to jump to commonly-used voltage/current limit combinations that you specify. That said, at home I have a Yescom power supply with a somewhat higher output current that’s useful for testing RF amplifiers, and its analog controls make it somewhat easier to smoothly vary to the output voltage and see how a circuit/amplifier reacts. If I had to choose only one, I’d get the Hanmatek (or one of its many clones), but an analog-controlled meter is handy for certain situations. (I got by with an Elenco Precision XP-656 500mA 0-30V DC supply as my primary current-limited supply for years.)

The Hanmatek interface (top right) is a little unintuitive, but the manual is decently written. It’s sitting on top of an older tri-voltage power supply.

To connect your power supply to your board, you’re going to need an assortment of wires and connectors. A handful of the typical USB cable types (A-to-Mini, A-to-B, A-to-Micro) is useful, and you probably already have them floating around in your sock drawer. Generic alligator clips are always handy. Mini-grabber style test leads are great for hooking to component leads on a breadboard, though they’re not rated for much current – in those cases, a beefier clip lead is a better choice.

While most projects are going to be DC powered, having enough AC outlets to have all of your test gear plugged in all the time, plus plenty of outlets for temporary plugs, plus a few more, is a tremendous timesaver. You can snag a multi-outlet power strip for relatively cheap these days, but they’re also really easy to find at garage sales, fleamarkets, and swapmeets. The Amazon Basics 6-plug power strips used to be dirt-cheap, like \$3 for a two-pack, but as of this writing they’re now \$10 for two… a bummer, those used to be a real steal.

If you’re ever in doubt about the functionality of an AC outlet, or if you’re going to be taking your work to a place where AC wiring may be questionable, a cheap outlet tester is useful – it will confirm the presence of AC voltage, whether the hot/neutral are reversed, and other incorrect-wiring hazards. If you just need to confirm whether an AC circuit is hot, a non-contact voltage detector pen is the easiest tool to use – just hold the on-button and place the non-conducting tip near the (potential) AC voltage. If it beeps and lights up, there’s some AC present. Be warned though – the presence of AC-something is not a guarentee of 120 volts or 15 amps or whatever you actually need, just that there’s some fluctuating voltage nearby. Just last week I watched an electrician get mislead by his NCV on a three-phase system – his pen told him all 3 phases had AC, but when he got around to actually sticking his meter probes in the test points, one of the phases was only “33V” to ground (i.e. the system had dropped a phase). You’ve been warned!

### Power Tools

While I don’t often use a power drill for actual workbench projects, the ability to stick a screw in a wall or quickly knock a hole in something is nice. I received a cordless Black and Decker 20V drill as a gift years ago, and its been sufficient for my home purposes ever since. Sure, at the point in my career where I was putting 3/8″ lag bolts into 2″ of plywood, the building had standardized on Ryobi impact drivers, which are much stout-er. But the’re also more expensive, and for home-use, I just don’t usually need that much firepower.

My old accomplice turned my on to the virtues of an electric screwdriver. Why would you need an electric screwdriver when you have a high-torque, high speed, large battery drill? Exactly because the electric screwdriver is lightweight, low-speed, and easy to transport – you’re not using it to drive screw into material, you’re using it to take machine screws out of an electrical panel, say. Or install a hundred rack-mount screws. Or take out and reinstall a Euro-rack module 60 times. The light weight and ease-of-use of the screwdriver limits fatigue over long projects like these. Black and Decker makes a fine, inexpensive model.

We’ll get into the virtues of heat shrink tubing some later day when we dive into materials, but an inexpensive heat gun is the appropriate tool for using it. I started with a \$10 model from Harbor Frieght which lasted 5 years, and then bought another \$10 to replace it. The trouble with all heat guns under \$100, it seems, is ergonomics. After you’ve used the gun for a couple minutes and brought the metal tip to a searing-hot temperature, what do you do with it? This Porter-Cable model, with a flat-but you can stand up on your workbench, is the best solution I’ve seen. (Professional models have a flat or angled plate on the back to stand up in just this way.)

### Hand Tools

A few basic hand tools will go a long way in making your workbench serviceable and ready to tackle common challenges – some are worth a little investment, while others are prime fodder for the cheapo Harbor Freight model. And thankfully, there are a number of tools where jumping from the \$5 version to the \$10 version makes a world of difference, and is worth the Lincoln.

There are lots of different tools to strip insulation off of wire – manual strippers, semi-automated strippers, fully automated stripers, a par of cutting pliers, a knife, your teeth… not that I would recommend all of those. But you can’t really go wrong with a basic set of wire strippers that covers gauges from 10 to 30 AWG. These Paladin wire strippers were our go to at my last job, and they fit the bill just fine. The curved handle takes a little getting used to, but it actually makes them pretty ergonomic, which is nice if you’re splicing a couple hundred bits of wire to LEDs in an afternoon, say.

A decent set of flush cutters is also worth a minor investment – not more than \$7-8 a pair, mind, just don’t get the \$3 ones or they’ll fall apart. Flush cutters are the tool of choice for trimming the leads on components, say, but they’re also great for getting a clean end-cut on a piece of wire, or trimming flashing off of 3D-printed models. On the advice of my accomplice at my old job, we’d order 5-packs of Hakko-brand flush cutters regularly, and they served us well. For less critical cuts, a couple pairs of scissors is handy, though for papercraft I prefer single-edge razor blades.

Small pliers are something you can go the inexpensive route on – Harbor Freight or eBay ones would be fine, you’re usually not going to be putting so much force on them that you’re in danger of damaging them. This set of 6 assorted pliers for \$20 I ordered for my new workbench has been pretty solid – the extra long, extra thin needle-nose pliers I keep near my 3D printer for pulling ooze off the nozzle right before a print. Having a few heavier duty pliers around is often helpful – just a basic lineman’s pliers for when you need to put some force into the work would be a good place to start.

One of my favorite pairs of pliers – long thin nose, good grip, and \$2 at the hardware store.

I must confess – I don’t find the sets of “one small screwdriver handle and 1700 bits” to be terribly practical. They’re great to have around for special projects, but the extra time spent swapping bits back and forth for every project/object/screw is  wearisome. As daily driver small screwdrivers, I much prefer a set of basic jewelers screwdrivers in philips, flat, and hex. This Wera 12-piece set is my go-to recommendation these days, and the carrying-case is nice if you don’t have permanent storage set up yet or if you’re throwing your screwdrivers in a toolbag.

Decent screwdrivers that don’t strip themselves instantly, in a nice carrying case too.

A basic 6-in-1 screwdriver suffices for most large screwdriver needs. That link is the cheapest one I could find on Amazon, but honestly, they’re often between \$1 and \$3 at any hardware store, grab a couple then next time you see one.

It’s amazing how cheap digital calipers have become – less than \$20 for a decent 6″ caliper that does decimal inches, fractional inches, and millimeters. The calipers are among the top-five most commonly used tools on my bench, along with the soldering iron, pliers, and screwdrivers. You can measure interior dimensions, exterior dimensions, depth, diameter, all with a precision unmatched by analog means. Get yourself a set, it will change your bench. For larger measurements, a basic tape measure is handy – no need to get a fancy one unless your carpenter-ing regularly.

20 years ago, these would have been a multi-hundred dollar item. Now they’re basically disposable.

I wish I had a more in-depth knowledges of adhesives, epoxies, and glues. The properties department at the theater I used to work at maintained an encyclopedic knowledge of which glues were best of which applications, which chemicals were safe for which materials, which drying-times would lead to problems with material interactions… it was stunning. For my general purposes though, there a few basic adhesives that get me through the day more often than not.

Hot Glue is a tremendously versatile material – you can stick most (rough) surfaces together with it, you can build up gussets and supports with it, you mold it to shape a little, and it removes easily from most things except paper. And did you know it comes in black? A decent 100W hot-glue gun is a great “well this just has to hold a little while” solution.

For more permanent fixes, cyanoacrylate glue (also known as CA glue or the brand names Super Glue or Crazy Glue) is a good go-to – it bonds to most things with a slightly-rough surface (so roughing up, say, metal with a file first is a good idea). It hardens in the presence of moisture – atmospheric humidity is enough, but if you put a big glob on something, the outside layer will start to set first and slow the setting process of the inside. Use only a thin layer to reduce this issue – in the right circumstances, the glue will set in a matter of seconds. If you need a little bit more working time or pliability, E6000 Adhesive is a better choice.

Very High Bond double-sided tape (VHB) is an amazing product (well, line of products) from 3M. They give you the versatility of double-stick tape with some crazy adhesive capabilities. 3M’s full catalog of adhesive tapes is worth browsing if you’re into that sort of thing. As a good default, their RP62 foam-tape is strong, slightly spongy (good for bridging irregular surfaces), and relatively inexpensive.

For adhering large sheets of goods together, especially paper products, some kind of spray adhesive is going to be easier to use than a brush-on or dab-on variety. 3M’s Super 77 is the de-facto standard spray adhesive for light- and medium-duty applications – adhering paper to paper for scrapbooking, or laminates to sheet goods. Simply spray Super 77 onto one of the surfaces, wait 60-90 seconds for the adhesive to become slightly tacky, then smoothly lay the second material onto the first. For heavier applications, there’s a High Strength 90 spray adhesive that works much the same.

I’d be remiss if I didn’t mention thistothat.com, a website that generates recommendations if you want to glue this material to that material. Want to stick ceramic to rubber? They’ve got a solution to that, and lots of other combinations as well. Well worth a look.

### 3D Printing

I know I said I wouldn’t get too far into specific materials or specific arenas of work, but having a 3D printer in your electronics workshop opens up a whole world of mechanical possibilities. Whether its custom enclosures for new projects or quality of life improvements for the shop or project mockups or practical tools, the sky’s the limit of what you can accomplish. Getting started in 3D printing could be a whole series of articles in and of itself, but for the moment let me confine myself to some recommendations of tools to facilitate the practical use of 3D printing on an electronics workbench.

To start, the printer itself. I don’t have any experience with SLA 3D printing, only the more traditional FDM method. An FDM 3D printer is essentially a fancy robotic hot-glue gun on rails, that moves precisely around a 3D space squirting out hot plastic as it goes, which sets into shape as it rapidly cools down. This is a relatively speedy way of printing an object, but the spatial resolution of the resulting object is limited by the resolution of both the stepper motors that push the print-nozzing around and the diameter of the print nozzle. Still, with a stock 0.4mm nozzle and a basic machine, some really beautiful things are possible.

How do YOU control your hot-end?

If I were to recommend a first FDM 3D printer to someone today, it would be the Original Prusa MINI. Josef Prusa was one of the original movers and shakers when the hobbyist 3D printer train was getting rolling in early 2010s, and his i3 model is perhaps the most popular 3D printer in the world. With a reputation for a great product and great customer service, the release of a printer at that key \$350 price point that’s become so popular, with mesh bed leveling, a heated bed with removable build-sheets, ethernet connectivity with WiFi upgrade possibilities, an option filament run-out sensor… I’m very excited for this thing. It’s currently on pre-order for \$350 US to start shipping around the end of the year, and I think it’s going to be a slam dunk. When I think that i paid about that much for my Monoprice Maker Select V2.1 only 3 years ago, it’s amazing to think how far the technology has come.

This printer took a few mods to make the frame rock-solid. Amazing what 3 years progress looks like.

Of course, all of the specific nozzles, filaments, and accessories you need will be specific to your printer and your projects. But I can recommend a couple of tools that will be useful to all FDM 3D-printing setups, the first being a set of 3D printing spatulas. Most printers ship with a putty knife as their print-removal-tool, which is an excellent way to gouge a hole in your print surface (or your hand!). Since receiving a set of these spatulas as a present for Christmas last year, they’ve easily become the tool I keep closest to the printer.

These were definitely sitting on a shelf somewhere as palette knives and someone thought “you know what we could sell those as? 3D printing spatulas!” But they work, so who cares.

Second, while there are lots of methods of getting your 3D print to stick to the print bed, keeping the bed itself clean of oils and debris goes a long way toward success. I keep a bottle of high-strength isopropyl alcohol and some lint-free clothes nearby to wipe down the bed between every few prints, just to make sure the residual oils from printing and from my hands don’t cause premature liftoff from the print bed.

### Software

In this digital age, MS Paint is just as practical a tool as a paintbrush. So let’s not leave out the digital tools that we use to make, track, distribute, and record projects on the workbench.

For 2D drafting, my two primary tools are AutoCAD and Vectorworks. AutoCAD (made by AutoDesk) is an incredibly powerful CAD program, and it’s been around forever. Want to model a bracket, or a whole airplane, or design a building, or pocket watch? AutoCAD can do it. It does have a fairly-steep learning curve – there are folks who make entire careers out of just working in AutoCAD – but it gives you a lot of power for your trouble. Vectorworks is a less-commonly-used program that I became very familiar with in my years as a stage lighting technician; due to its excellent stage-lighting plugins, it’s the de-facto standard for theater lighting. And where AutoCAD focuses on building a “model” and having you derive drawings from that model, Vectorworks focuses on the drawing itself as the thing to be made. It might seem like a semantic difference, but the way that those philosophies influence the workflow of the two programs means that Vectorworks is often my choice for creating 2D draftings.

For 3D drafting, my go-to software is Fusion360, also from AutoDesk. Fusion is a timeline-centric, parametric drafting program, which allows you to go ‘back in time’ to an earlier moment of a design, make changes, and see them ripple through to the current version of the design. It’s a very powerful program, though not without its own learning curve. For someone just diving into 3D modeling for the first time, I’d recommend starting with something like Tinkercad, a cloud-based modelling program that centers around adding and subtracting primitive objects from each other to build up a more complicated design. I’ve also had friends work in SketchUp, which tries to blend Fusion’s 2D sketch capabilities with the ease of Tinkercad. Unfortunately, SketchUp seems to have trouble successfully exporting STL files for printing, so I can’t recommend it as a strong starting point.

Fusion is a very powerful, very worth-learning program.

Once you have your 3D model and you’re ready to print it, you’ll need a slicer program to turn the model into a series of step-by-step instructions that the printer can actually follow. (“Move to such-and-such coordinates in so-many seconds while extruding this-amount of plastic“. Repeat x10000). I personally use Cura, now from Ultimaker. It’s straightforward to use, and has all the options and customizability I’ve found a need for. I know lots of folks who have good opinions about the open source Slic3r project as well.

Programming and text editing may or may not be a part of your electronics hobby, but if they are, having simple straightforward tools is a good way to get more productivity out of your text-based time. Of course for programming Arduinos, the Arduino IDE is a perfectly good place to start. It’s not fully featured in an respect, but it just works, you can write code in it and plonk it on an Arduino, and that’s all most people care about. I use Sublime Text as my main text editor and sometimes basic dev environment (when writing things in Love2D, for example).

For projects that are just too detailed to lay out by hand, I design circuit boards in AutoDesk’s Eagle software, though there are some who would say I’m a heathen for not using the open source KiCad. To be honest, I don’t have strong feelings about either software either way – Eagle was just the first one I used and I’ve become used to its workflow and design choices, but I know there are die-hards on both sides of this river. Regardless, to live in an age where a maker has multiple, quality options for free PCB design software is amazing.

I would never in a million years be able to achieve this level of miniaturization with a hand-fabricated board.

Of course, once you’ve designed a circuit board, you’re going to need to make it, somehow. While they’re not software per-say, the growth of PCB shopping cart websites over the past few years has really opened up what’s possible for the solo electronics workshop. No more sweating with getting tiny wires soldered to tiny chips to break them out to veroboard; you can just spin a PCB with the proper footprint, or indeed the whole circuit. Any of these services will let you upload your circuit board design, and for a very modest fee spin you up 3 or 5 or 500 copies. OSHPark really started the whole small-batch-PCB movement, and their service has always been great, reliable, and high quality. I’ve also used JLCPCB for somewhat larger runs. If you’re interested in looking at many, many options, PCBShopper is an aggregator that lets you compare prices, lead times, and options across almost two dozen shopping cart-style manufacturers.

### Safety

Just because you may not have a giant 5-axis robot in your workshop doesn’t mean you shouldn’t take safety seriously. Whether your workshop is in your home, an outside shop, or your workplace, a few basic safety precautions could mean the difference between peaceful Thursday and a trip to the ER.

Smoke and carbon monoxide detectors should be present in several places in your home or office already, but having one in the workshop is a good idea, especially if you have any hot-tools (soldering iron, heat gun, 3D printer). They’re so inexpensive and easy to install, it’s a no-brainer to pick one up. A fire extinguisher should also be on your list – and if you ever have the opportunity to get a little training on how to properly use one, it’s well worth it. Make sure to mount your fire extinguisher where you could actually get to it, if the things that are most likely to start a fire, did.

I put my fire extinguisher right by the door to my workshop, so I can grab it on the way in, or on the way out.

While we’re thinking about fire, consider whether your workshop needs a flammables cabinet. If you’re storing more than a few things of paint, spray paint, spray adhesives, solvents, cleaners, etc, it’s worth thinking about what would happen if they were to catch a little on fire. It’s not usually worth buying on online – the shipping is killer- but cabinets pop up on Craigslist, auctions, and industrial surplus all the time. Go Industry Dove Bid is a good online collector of industrial surplus auctions, but be sure to check out your local city/state surplus resources as well.

Finally, safety glasses. Just wear them, even when you think you don’t have to. About 4 years ago, while soldering “just one more joint” on a PCB before going to bed, a piece of hot solder popped up and got me in the lower-left eyelid. A quarter-inch higher and it would have been right in my eye, with who knows what consequences. I’m not always perfect about this myself, but I do keep a pair of safety glasses right on my workbench to remind myself that if I want to take a risk, it’s my own damn fault. Get a pair of glasses that are comfortable so you’re more likely to wear them.

### Organization

No such thing as too organized.

I’ve come to realize something over the past 10 years – the most volume I’m willing to rummage through for a tool, part, or piece is about 500 cubic inches, or a around 10 liters. Any more volume than that, especially for small parts, and there’s just too many potential places where a small object can hide. So standardizing on a storage bin that’s slightly smaller than this makes good sense. At home, I use 6-Quart Bella bins from Menards, while at work I use 6-Quart Sterilite bins. Once a project or set of components or tools overflows one of these bins, there’s probably enough diversity in goods to split it up into two separate bins anyway – i just recently split the Microcontrollers bin into Arduinos and Non-Arduino Microcontrollers, for example. Now both species are easier to find.

So many pretty bins, all in a row.

I’ve always loved a good whiteboard (I just snagged another 18″x24″ one for my office), but I recently stumbled upon these ultra-fine tip whiteboard markers, which I just absolutely love. They allow you to squeeze so much actual detail and small size into a whiteboard doodling project. Not for presenting to a group, mind, just for working through projects on your own or with a partner. (I also 3D printed a cup for them for my kitchen whiteboard calendar, more on that in a future post I think.)

I’m a strong believer in the power of labeling to make things just so, and a labelmaker is a really easy way to help keep things organized. The Brother PTD600 has been a nice blend between portability and computer control – you get most of the functionality just using it handheld, or you can hook it up to Brother’s software on your computer to make more complicated layouts, batch prints, etc. The sound department at the theater I used to work at had a Rhino BMP21-Plus, which was really awesome at making self-laminating labels to label cables – with the amount of work that went into cable arrangement and maintenance in that place, the self-laminating labels were a godsend. The tape’s a little pricey, as is the labeller, so if you’re not doing a lot of patch panels, say, I would stick with the Brother and the TZe line of tapes.

### Lighting

Decent task lighting makes a world of difference – you’ll find you’re suddenly better at soldering, more deft at assembly, swifter to catch errors and notice mistakes. No sense working in the dark if you don’t have to.

I’ve done a number of lighting setups in my home workshops over time. Right now I have three 24″ fluorescent fixtures overhead that were remaindered from a theatre production ages ago (in addition to a basic 100W ceiling light). I’ve also got a couple of clip lights with 100W LED bulbs closer to my actual workbench surface to price more focused task lighting, and a cheap gooseneck light from IKEA sitting on the work surface for when I need really targeted illumination. While I haven’t re-installed it since I moved into a new home workshop a few months ago, adding under-shelf lights to my home shelving setup made a big difference in being able to see and find components on the shelves, as well as adding some cheery glow to the workstation. My workshop at work has lots of overhead fluorescent light, and I added a positionable jointed lamp for some more focused lighting.

If you’re still reading this 6500 words later, you might thinking – “Holy crap, that’s a lot of stuff, I’ll never be able to have my own electronics workbench”. But keep in mind – this is the setup and tools that work for me, with what I want to do, that I’ve built up over a decade of working professionally and as a hobbyist in this arena. Would you look at a professional auto mechanic rebuilding an engine and say “Wow, I’ll never open my hood again?” It’s all a matter of starting somewhere.

Two apartments and many years ago, this is what my “workbench” looked like. And it was still a BLAST.

The easiest way to pick a project is to find a project you want to accomplish and work toward making it happen. Maybe it’s monitoring to see whether your garage door is open or closed. Or what the weather’s going to be tomorrow. Maybe your dog needs some entertainment, or you need a new sparkling light over the crib, or the you have an itch to build a radio or a tesla coil or who knows what. Once you find a thing you’re excited about building, that will guide you as to which tools to find first, which will lead you to more things you can do with those tools, which will lead to more tools… and so on.

And most importantly – have fun.

### Special Thanks

I wouldn’t have been aware of so many of these tools, ideas, and possibilities without a lot of excellent colleagues and friends. Thank you especially to Kenneth, Palmer, Alec, Joe, Mike, Jabin, Lee, Travis, Chris, and all the other excellent technicians who continue to be an inspiration for excellent technical work.

Also, just in the interest of disclosure: most of the Amazon links above are affiliate links. Purchasing through them provides a small amount of compensation to me at no cost to the buyer.

# Closet Door Locker

Yesterday I install a new closet door in our front entrance hall, and discovered a problem which I then solved with 3D Printing. The door is a standard bi-fold type, with pins in the top and bottom of one side for rotation, a central vertical hinge, and a track along the top to keep the far side in alignment.

The problem was – with the volume of coats we need to survive a the winter on the ice planet Hoth (Chicago) and the positioning of the hanger rail, the coats push the door out and prevent it from staying fulling closed. Given that this is immediately adjacent to the front door, not an ideal solution at all.

There are lots of types of locks/clasps/magnets designed to solve this problem, but the one I chose to emulated is this over-the-door babyproofing product. It’s essentially a c-channel of plastic that slides over the middle-hinge when the door is closed, to prevent it from swinging open. Genius.

I created my own variant in Fusion360, thinking about how to make the design rigid, printable, and aesthetically pleasing. I added ridges along the sides to increase its lateral strength, and little pull-tabs to make it easier to grip. I trussed-out the top to give it some additional strength and reduce weight. Here’s how it ended up after about an hour of drafting:

Printing took a little over 10 hours, and the final result works great. I selected a blue-green PLA+ for ease of printing and aesthetic considerations:

Thanks 3D printing!

# 3D Printing in the Home Workshop

With the bulk of the shelving and organization overhaul complete as of last week, I’ve spent the last week starting to personalize my home workshop space, mostly using my 3D Printer. This is definitely a situation of “when your favorite tool is a hammer, everything looks like a nail.” And the 3D printer is an awfully nice hammer…

There are some things that 3D printed plastic parts are perfect for, including:

• Brackets to attach/connect unusual shapes
• Containers/guides for specific materials and tools
• Stands and supports for lightweight goods

But of course, there are some properties that 3D printed thermoplastics are always going to be underachievers in, like:

• Brute strength (compared to metal or wood)
• Tiny mechanical details (like screw threading)
• Heat resistance

In my mind, an ideal setup picks and chooses the materials that are right for each job. There’s not much point in printing, say, a 24″ wide shelf when a wooden one with be stronger, cheaper, and easier to make or buy. Conversely, welding a microphone stand together out of metal would be a nightmare, where it’s easy to print an existing plastic design that will hold up just fine.

The thrust of this is that, with the ELFA shelving (wood and metal) providing the backbone of my setup, there’s lots of space to fill in the operational edges with 3D printing. I can’t possibly cover every print, but in no particular order, here are the new additions to the setup, and some most-useful oldies:

#### ELFA Corner Bumpers

I designed and printed these the same day I finished the shelving install, after my partner nearly beaned herself on the corner of a shelf by the doorway as she was getting up. They’re a tight enough fit that they stay out without adhesive or fasteners. The design is now on Thingiverse.

#### ELFA Cable Guides

With the number of things that plug into AC power on my bench, I figured cable management would be useful. I started by putting together an ELFA Shelf Hook Profile, which can be used as a basis for anything that hooks into the ELFA vertical standards. I then added an L-hook shape to one side of the profile, which captures any cable that are hooked into it before the piece is installed. This is the result.

#### ELFA/2020 Bracket

I’m trying out using a piece of 2020 extruded aluminum as a generic mounting rail for some desk equipment, including the camera arm below. Maybe I’m being precious because the shelving is still new, but I couldn’t bring myself to put holes into the front of the shelves to mount this rail in place. I designed and printed these brackets, which are a tight fit to both the front of an ELFA solid shelf and the 2020 piece, and further secure to the 2020 with a screw and a hammer nut. A small piece of blue-tak can be fitted to the slots on the underside to prevent the bracket from sliding off.

This will probably need a second draft, as I realized after installation that they don’t leave room for the LED lighting I intend to install under each shelf.

#### Lighting PSU Wall-Standoffs

I’ll get into the lighting for the room more once all the parts arrive on the slow boat and I can get it all installed. In the meantime, I’m starting by mounting the 30A, 12V PSU. The positioning of the vertical standards on my wall didn’t leave an obvious place to mount the PSU, but the unit does have four M4 threaded holes on the sides. I designed and printed these mounts to accept up to three drywall screws each, with a slot and countersink for an M4 screw.

#### Articulating Camera Arm

Having a semi-permanent camera on my desk has been useful for project documentation. This is an assembly of two prints by other makers – RaffoSan’s Universal Camera Mount and Felwats’ C920 Adapter. The adapter actually fully replaces a piece of metal that sits between the camera and its original hinged arm. The arm mounts to the 2020 rail previously mentioned, which is mounted on the front of the lowest shelves.

#### Oscilloscope Probe Holders

This design popped up on the FunctionalPrint subreddit just in time. I was struggling with what to do with my scope probes – coil them next to the scope, keep them in a bin and pull them as needed… this solves that problem. The design comes from JRucks and is now on Thingiverse.

#### ‘Hot Shoe’ Microphone Mount

I’ve had this one kicking around for awhile to hold my cheapy Takstar SGC-598 microphone. It’s not the fanciest setup, but for my casual purposes it’s more than enough. The design comes from Asgeirom on Thingiverse.

#### Solder Roll Holder

I didn’t really see the point of having a solder-roll holder until I printed one. Never again will that 1 lbs roll go walking across the desk (or onto the floor) in the middle of a tricky joint. This design comes from Phredie on Thingiverse.

#### “Pencil Cups”

These multi-purpose cup was one of the first designs I ever printed, and it’s still my go-to print for sampling the color of a new filament. It’s meant to print in spiraled-contour mode, which means that the outer perimeter (after the base) prints in one continuous revolving motion, instead of stepping up layer by layer like a typical print. There are perhaps a dozen of these scattered around the apartment, but since the reorganization, most live just above my desk holding, individually: pens/pencils, colored sharpies, black/silver sharpies, screwdrivers, pliers, flush cutters, cutting tools, and misc tools.

The next improvement to my setup is definitely a lighting improvement – its not terribly bright in the room to start with, and the shade from the shelves doesn’t help. 3D printing will be involved.

I also put my new setup to the test for the first time last night as I laid out a version of a DMX shield for the Arduino Pro Mini. Having all my tools organized and close at hand, and plenty of space to work it, makes working in my new setup a joy. The cleaning, the organization, the installing of new systems and setups: all worth it. It’s now fun to sit at my workbench, instead of a kind-of cramped pain. Onward!

# 50W QRP Amplifier – 3D Printed Case Design and Livestream

1.  With the 50W QRP amplifier project coming along nicely, I felt it was time to start thinking about a reproducible case for the project. And for custom, reproducible cases, 3D printing is my current tool of choice.

I ended up designing the case on a YouTube Livestream on Saturday night, to which a few great colleagues stopped by to ask questions and offer advice. The full video is below.

The case is in two parts – a box with standoffs for the PCB and holes for connectors, and a lid with labels. The standoffs and the attachment holes for the lid are meant to connect with M3 threaded-inserts and be held down with M3 machine screws.

This was my first time using Fusion 360’s Eagle Sync function – since Eagle PCB design software was acquired by AutoDesk in 2016, it makes sense that they’ve been working to integrate PCB design workflows into their other products. The sync was fair straightforward – open Fusion360, select Eagle Sync, select your board file in Eagle, and after a minute or two of importing, up pops your PCB in Fusion360. Neat! I’m still struggling with how to handle board cutouts in eagle, and I’m not sure how well they’ll be supported in Fusion, but that’s a project for another day.

Here’s the final design as it turned out in Fusion360:

The PowerPole model was provided by Chris Wych, a theatrical propmaster who’s done some really interesting work with Fusion360, including using it to model some 2d-printable geodesic designs which then folded up into geometric shapes. Very cool!

First print of this design coming soon!

73

This post is cross-posted to my ham-radio specific blog, kk9jef.wordpress.com.

# Geared 7-Segment Display, Part 4 – Pinion Gears and First Rotation

This weekend I’ve added the pinion gears to the seven-segment display, and performed the first test rotation of the mechanism.

As previous noted, the arm gears are 6-tooth gears of module 4 (metric) – in clockmaking terms, these would be pinions. In the clockmaking world, where I’ve been doing quite a bit of research during this project, there doesn’t seem to be a hard dividing line between what’s considered a “gear” and what’s considered a “pinion,” except that gears are big and pinions are small. Fair enough. From this point forward I’ll be referring to the arm gears as arm pinions.

I printed 6 of the pinions in just over an hour, and fitted them to their axles, which are just hacked-off pieces of 1/8″ rod stock from the hardware store. With the tolerancing on the prints as it is, the pinions are a snug fit on the axles, so I’m not too concerned about slippage once I can get the whole thing turning smoothly.

Speaking of turning, here are the first (partial) rotations of the mechanism.

https://youtu.be/mj-Oc7rT6L0

Right now, the biggest impediment seems to be that the frame lacks rigidity, and easy warps and slews far enough to drive the arm pinions out of mesh with the drive gears. I’m currently working on a two-part version of the frame with interlocking members that firmly affixes both halves on the frame so that they remain rigid and parallel.

I’d assumed when I started this project that the axles (arbors) would need to be made of metal rod or dowel stock, so that they were firm, perfectly round, and rigid. But this being a 3d printing project, I’m now experimenting with a fully3D printed arbor-and-arm-pinion assemblies. These have the advantage that there’s no need to manually locate the pinion on the arbor by sliding the arm pinons up and down the arbors – they’re all one piece. As a sample, I printed a C-Arm assembly in two different orientations, both vertically and horizontally:

The vertically-printed arbor and pinion came out much better – the axle on the horizontally-printed unit is limited in smoothness by the layer height of the print, while on the vertical print it’s limited by the X and Y resolution of the printer. Additionally, while there is significantly more support plastic on the vertically printed unit, it’s not touching any of the working surfaces of the pinion itself, making the post-processing and filing significantly simpler. Both seemed to rotate well in the axle holes, however; well enough that I plan to work up a full set of these and test them in the next version of the frame. That means the only non-3D printed part in the project would be the main axle, and possibly the G-Arm tubing.

Next steps are printing the stiffer frame and the pinion/arbor assemblies.

# Geared 7-Segment Display, Part 3 – Drive Gear Interlocks

The heart of the seven segment display is the seven drive gears with select teeth, which share a common shaft and all rotate together. As I was developing the idea of the drive gears and conceiving of how the presence/lack of teeth could “signal” the arm gears to turn or not, I though of them as plain, 2-dimensional shapes. I had planned on spacing them out along their common shaft using 3D printed washers of a set thickness. As for aligning them at the appropriate relative rotation, I thought I might print a jig (some kind of tall internal gear) to hold all the drive gears in the right relationship. Then I would either affix the gears and washers with superglue, or drill an alignment hole through all 7 gears and insert a small alignment rod to maintain their orientation.

Here are the first three drive gears (A, B, C) with a 2mm-tall washer between each. Looking good!

But this is thinking like someone who only has access to subtraction manufacturing. Why carve out a hole and insert new material when we could print the holes and alignment rods as part of the gear themselves?

I took another pass through all the drive gears, and added two 3mm wide, 7mm long “pegs” to the front side of each one (except gear A, the front gear). I also carved out a matching “slot” in each gear to receive the pegs behind it, with 0.3mm of clearance in all dimensions. (0.3 is my standard clearance value when I want two mechanical parts to fit together with no problem at all – your experience may vary.) Additionally, I extruded the center portion of the gear an extra 3mm upward to eliminate the need for the spacing washers I’d previously planned on.

Here’s the new E gear as an example:

You can see the two protruding rectangular “pegs” on the top that fit into the D gear, and the two similar slots on the bottom that receives the pegs of the F gear.

So, here’s what all 7 interlocking gears look like on an axle:

I whipped up a couple of minimalist end-frames to hold the drive axle and the axles for the arm gears – with both front and back in place, the mechanism is starting to take shape:

These endframes are a good example of something I’ve noticed with mechanical objects and additive manufacturing – there are huge time paybacks for small investments in drafting time. I’d first conceived of these end-frames and simple, 2mm thick rectangles with 7 holes in them. Cura estimated that each of those plates would take around seven and a half hours to print. Oof! There goes the weekend. But another 15 minutes of casually cutting things away in Fusion360 and the resulting frame took about two hours and 45 minutes. That’s ten hours of printing time saved with a quarter hour of drafting, a massive return on time invested.

Next step will be to re-print the pinion arm gears with appropriate axle holes, and then test fit the gears together. Here goes nothing.

# Geared 7-Segment Display – Part 2, More Gears

While time at home is scarce this week, I’ve stolen a couple moments late night to continue working on the design of the geared 7-segment display, including finishing the modelling of the 7 drive gears.

Each drive gear is based on a 30-tooth, involute gear of module 4. Each segment of 3 adjacent teeth represents a single transition of a segment (or lack there of) – if there are teeth in a segment, the associated arm gear will rotate, changing a segment from active to inactive for a given transition or vice versa.

As a side note, each gear has a even number of teeth remaining, and each segment makes an even number of transitions as the display makes a full cycle of ten digits. If a segment made an odd number of transitions, it would start the next “cycle” in a different state than on the previous cycle, causing the numbers to “look” different on each time a given number came up, which is clearly wrong. This served as a useful sanity check as I was working through each gear in turn.

Here is the mechanism in its current Fusion360 form (support plates, arms and mounts, and a drive mechanism yet to come):

The A, D, and G arm gears lie on the vertical axis of the mechanism. The A and G arm gears, as noted in my previous post, are currently intended to be co-axial, the shaft of the A segment being a small hollow tube which completely surrounds the shaft of the G segment. Of all the details in this mechanism, this one seems the most fiddly at the moment, since any tolerance issues are going to compound on each other.

The B, C, E, and F arm gears lie at ±50° from the vertical axis, which is just about as close to the vertical axis as they can be and still have their arms clear the axes of the A/D/G segments.

In contrast to what I said a the end of my last post, I’m thinking I’ll print each of the gears individually and then mount them on the center axle with spacer washers. The whole-gear-assembly-as-barrel has one fatal flaw: printability. That’s a lot of overhanging teeth to worry about. That said, the print-individual-gears approach means needing to worry about registering adjacent gears to each other, but that seems like a solvable problem.

Looking down the road, here’s a quick Vectorworks sketch of how close adjacent digit displays could be. It seems I could squeeze them to about 175mm (~7 inch) centers.

Currently, the plan is to build one digit and evaluate… but the only thing better than N mechanisms is N+1 mechanisms…