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Fixing a loud PSU fan without dying

2025-07-30T00:00:00Z

Three months after I built my new computer, it started annoying me. There would occasionally be a noise that sounded like a fan was catching on a cable, but there weren’t any loose cables to be a problem. Over the course of a few weeks, the sound got progressively worse to the extent that I didn’t want to use the computer without headphones on. I measured the sound at 63 dB, which is about the sound of someone talking. That may not sound terrible, but it’s a constant, nasty noise coming from something that sits about 40cm from my head.

After some investigating¹, I identified the PSU fan as the culprit. I have a Cooler Master V750 SFX, which is not super high-end, but wasn’t cheap, either. It shouldn’t be developing issues after three months. Thankfully, it comes with a ten-year warranty, so it should be easy to get sorted, right?

Warranty woes

I looked at Cooler Master’s warranty, and for issues within the first two years you have to deal with the retailer. That would be Amazon in my case. So I looked at Amazon’s information on warranty issues. Their policy is that if it’s more than 30 days since purchase, you have to send it off to a third-party repair center and wait for them to diagnose and try to repair it. Here’s the kicker:

Usually repairs take up to 20 business days (including delivery time), but could take slightly longer

I use the computer for work, have upcoming LAN parties to go to, and generally can’t do without it for an entire month. That’s assuming they reproduce the issue: the PSU fan only turns on when it reaches a certain temperature, so if you just plug it in briefly it won’t exhibit any symptoms.

If I was going to do a warranty return, I’d need to buy a new PSU first to use while this one was away. If I’m spending £100+ on a PSU, then I’d be getting a better one that doesn’t have known issues with the fans. So when the Cooler Master eventually got returned I’d have no use for it. What a waste.

So the warranty is about as much use as a chocolate teapot. Good to know, I guess. If I wanted decent service, I should have probably used a real retailer, not Amazon. Lesson learnt.

Doing some research

If the warranty is useless to me, maybe I should just void it and try to fix it myself. I did some research online. Most of the results went like this:

if you’re not a trained professional you should not be opening up your PSU at all. There’s a lot of current that goes through it which will seriously hurt/main/kill you

it’s time consuming and potentially dangerous

or some other variety of doom and gloom. There were some actually useful results sprinkled in, though. A post on the smallformfactor.net forums details someone swapping out the fan on the 850W version of the same power supply because it was too noisy. It looks like the fan connector in the PSU is a two-pin connector, and they just used an off-the-shelf adapter to convert the standard four-pin case fan connector. It sounded a bit annoying to make it all fit, though.

A similar post on reddit showed basically the same upgrade, but identified the connector as a 2.54mm JST-XH. They crimped their own connector on, which feels a lot better than using a bulky connector. I do have a crimping set for JST connectors, but I absolutely hate doing them because they’re so fiddly and annoying. I’m not sure if I trust one of my crimps inside a power supply, either.

Looking at the pictures in those posts, I identified the fan as an Ong Hua HA9215VH12FD-F00. I searched to see if I could see any specifications for it. I couldn’t. But what I did get back as my first result was another Reddit post, this one titled “Getting rid of a HA9215SH12FD-F00 fan from your PSU”. It says something about the quality of a component when the first result is a post about getting rid of it because it’s annoying².

All of these mods seemed easy enough, and I’m reasonably confident in my ability to both discharge and avoid touching capacitors, so I probably wouldn’t die. I ordered a Noctua NF-A9x14 fan and some pre-made JST-XH connectors and waited for them to arrive.

Upgrade time

The replacement parts arrived one evening, so when I turned the computer off for the night I unplugged it from the mains, held the power button down for a while, and left it overnight for good measure. The next morning I popped open the case, disconnected and removed the PSU, gleefully tore the “warranty void if removed” sticker off, and opened it up.

Removing the fan was simple: unplug the JST connector and undo the screws holding it to the outer panel. I confirmed that my JST connectors were the right size, then started surgery on the Noctua fan. I carefully removed the heatshrink, cut off the normal fan connector, and separated out the four wires. A quick check of their FAQ confirmed the wiring colours: black was ground, yellow +12V, and blue and green used for speed control (which we’re not using in this instance). I clipped the blue and green wires off near the hub so they wouldn’t be in the way, then cut the yellow and black wires down to length, and attached the JST connector with a solder seal:

Old fan, new fan, burnt mouse mat

In the process I discovered my mouse mat doesn’t like being hit with a heat gun. Whoops. The solder seals are great: the solder in the center melts to form an electrical connection, the parts at the end grip the cable to provide mechanical strength, and the whole thing acts like heatshrink and keeps the connection insulated. A lot less fiddly than crimping JST connectors, and a lot smaller and cheaper than an adapter.

I installed the fan and reassembled the PSU. Then undid it all and tried again, as apparently the face the fan mounts to isn’t quite symmetrical and I’d installed the fan upside down. Connected everything back up, plugged the computer in, booted it up, and… nothing. The PSU doesn’t actually power the fan until it hits a certain temperature. I figured putting it under load would probably heat it up, so ran a graphics benchmark a few times. Eventually the fan spun up. Huzzah.

Soon the entire computer will be beige and brown

Peace at last

I measured the sound of the new fan: 43 dB. That’s a decrease of 20 dB. Due to the weird logarithmic properties of the dB scale that no one understands, that means it sounds about 4 times quieter to human ears. Big improvement!

It’s worth pointing out this isn’t a straight one-to-one upgrade. I don’t know the specs of the old fan in terms of airflow, and I’m just assuming that the Noctua will be good enough by virtue of being a decent fan. They also behave slightly differently as the power ramps up: the stock fan starts spinning at a lower voltage than the Noctua, which needs around 7V to get started properly³. I don’t think this will be an issue, as it’s effectively just putting a small step at the lower end of the fan curve. It might shorten the overall lifespan of the PSU, but from my point of view it failed after four months, so any extra time is a bonus.

I recorded some before/after audio, so you can hear the difference. I think there’s some amount of volume normalisation going on, so it’s not quite as stark a difference as in person, but it’s still noticeable.

Audio sample from the old fan

Audio sample from the new fan

And if you couldn’t hear it, here’s a visual representation:

Side-by-side comparison of the audio clips

The whole upgrade took about an hour (less time than writing this post about it!), and I even managed to avoid killing myself.

Opening the case and sticking my ear near to various components. High-tech stuff. ↩︎
On closer inspection it’s actually a slightly different model — there’s an S not a V in the middle there — but I’m going to assume that doesn’t change much on the quality/noise front. ↩︎
It then keeps spinning down to about 5V or so, it just needs enough power to initially get started. ↩︎

Building a new Computer

2025-06-03T00:00:00Z

The finished PC. Cat pen for scale.

I recently¹ built a new computer, after exclusively using a laptop for three years. It’s also the first time I’ve departed from the usual combo of an Intel CPU and Nvidia GPU.

While the form factor of a laptop did make it amazingly handy for travelling and attending LAN events, it was starting to show its age and there was basically no sane upgrade path. The main problem was its 3060 mobile graphics card, which was okay for the first few years and then slowly descended into painful. At the time, the (fairly disappointing) 50-series had just been released, but hadn’t yet made it into laptops. Nvidia had stopped production on the 40-series beforehand, so there also weren’t any compelling options there, either.

That’s not to say there were no laptops at all that I could have upgraded to. There were. Just not really any that ticked all of my perfectly normal boxes like “run Linux”, “have at least 64GB of ram”, and “run modern games well”. Having to upgrade the entire system just because the graphics card was showing its age was a bit of a drag, too. So back to the land of desktop computers I went!

To try to preserve some of that convenience, I opted for a small form factor (SFF) case. The computer and all the accessories can fit inside a hand-luggage-sized flight case. More on that later, though.

Components, Choices, and Cramming

So what, exactly, is in this computer? The case is a Fractal Design Terra, which is a lovely little 10.4L case². My last desktop PC was a normal-sized Fractal Design case, which I liked a lot, and it seems like they’ve upped their game since then. The Terra is both pleasant to look at (just look at that wooden panel!), and a breeze to work in. The sides and top are fully and easily removable, giving you great access to everything inside³. I expected an SFF build to be fiddly, but the case made it feel about the same as a normal full-sized build⁴.

The case with sides and top off, and wires everywhere in desperate need of management.

Another nice feature of the case is the movable spine. I think this is relatively common in SFF cases, but it was new to me. You mount the graphics card on one side of a metal divider, and everything else on the other. The divider (or spine) can be moved side-to-side depending on what exactly you’re putting in the case.

As I mentioned earlier, this was my first departure from the Intel + Nvidia bandwagon. Nvidia’s 50 series was underwhelming, and Intel managed to put out a generation of chips that literally fried themselves. It seemed like a good time to try out AMD’s offering! I went for the newly released Radeon RX 9070XT graphics card, and a Ryzen 7 9800X3D processor⁵. The processor has a Thermalright AXP90 X47 Full heatsink on top of it, with a Noctua NF-A9 fan on top of that.

The motherboard is a Gigabyte B850I Aorus Pro, and it hosts 2 32GB Corsair Vengeance RAM modules, and a 2TB Crucial T705 NVMe drive. Powering it all is a Cooler Master V750 SFX. The PSU is modular to reduce the number of wires that need to be fitted in, but they’re still pretty big and bulky. I’m tempted by custom cables but they’re rather pricey, and you can’t actually see inside with the sides closed…

With the diminutive size of the case and all the components crammed in, there’s actually no room left over for case fans. The PSU, GPU and CPU all have fans attached, but that’s it. There are stories online of people having heat issues, but thankfully everything seems pretty happy in my setup. The components all draw in air from the sides, and the hot air passively vents out the top. If I keep the CPU under maximum load for a while then it starts to thermal throttle slightly, but the only time I’ve actually managed that is when compiling a kernel. Why was I compiling a kernel, you ask? Well, we’ll come to that.

But does it Linux?

I didn’t go into this build completely blind. I did a bit of reading and chatting, and it sounded like AMD drivers were pretty good on Linux these days. I didn’t check specifically if any of the components were supported.

The 9070XT was released on the 6th of March. I built my PC on the 26th of March. The first version of Mesa (the 3D graphics lib) that was generally stable with 9070XT cards landed in Arch on the 20th of March. If I did the build just one week earlier, I would’ve had a much less fun experience.

It still wasn’t quite perfectly smooth, though. When playing games I’d occasionally have issues. In some cases the screen just went blank and came back after switching windows, but in others the graphics drivers couldn’t recover and the PC needed rebooting. Fortunately the drivers are open source, and they have a public issue tracker hosted by the Freedesktop project. Searching through the issues, I found they’d already been reported (by another Arch user, of course), and there were various suggestions for work-arounds, as well as lots of work trying to reproduce the issue.

Within a week, an AMD developer had posted a set of patches that might address the issues, and asked people to test them. That’s fortunately pretty easy on Arch: you just clone the repository containing the PKGBUILD file, drop in the patches, and update the checksums for them. Then you start compiling, realise you didn’t tell it to use more than one CPU core, abort it, and start again but this time running on all cylinders. Soon enough I was running a patched 6.14 kernel and the problems stopped completely. Others reported similar outcomes, and the patches worked their way into the kernel proper.

I spent a few weeks having to compile a custom kernel every time I accidentally updated it (I should’ve just stopped pacman from touching the kernel for a bit…), then one day the patches didn’t apply because they’d been merged upstream. Since then everything has been perfect.

A friend commented that “this wouldn’t happen with Nvidia”. They meant it negatively, but I wholeheartedly agree! Maybe Nvidia have fewer launch bugs than AMD, but you absolutely wouldn’t be able to talk to their driver engineers on a public bug tracker, and get access to test patches that fix your issue. I’ll happily take a few bugs in exchange for a company that operates openly in a way consistent with the rest of the Linux community.

But does it travel?

Travel mode, engage!

So the computer works fine at home, but how do I get it to other places? I just shoved a laptop in a backpack⁶, but you can’t quite do that with a PC even one this size. I’d seen a few people at LANs who packed everything in flight cases, but they always seemed a bit unwieldy. Doing some research, though, I found that I’d just be able to squeeze everything into a flight case sized to be taken onto a plane as cabin baggage.

Peli (or Pelican in the US) are the most well known maker of flight cases, but I chose to go with Nanuk instead. Spec-wise they’re fairly similar. Nanuk are a bit cheaper. The killer difference for me, though, is that Nanuk publish STEP files of their cases. As someone with a 3D printer, giving me CAD models of things so that I can easily mod them is definitely a way to win my favour.

After lots of measuring and thinking and modelling I came up with an arrangement where everything could fit snugly into the case. The case has cutouts for the wheels and handles, which constrain what can go where. I ended up wanting the computer at the handle-end of the case to make best use of space, but that means it needs something to take its weight when the case is vertical. The solution was, of course, 3D printing.

Using the STEP files from Nanuk I designed an insert that spans across the case, with screw holes that line up with the ones in the flight case. I wasn’t sure it would be able to take the weight like that, so I also added in some supports in the other direction (running down to the bottom of the case, if it’s stood up). I ended up printing it in three parts, and it came out perfectly first time. I can’t emphasise how nice it is having CAD models instead of having to measure and guess at things.

With the support in place, I focused on cushioning the computer. I opted for 10mm thick EVA foam as it’s easy to obtain and work with, and doesn’t take up too much room. I used contact adhesive to glue the foam directly to the case and the 3D printed divider. There’s a piece that goes between the computer and the keyboard, so I printed some little 3D supports to hold that more firmly in place, and stuck those in with contact adhesive as well.

So how does it all hold up? It’s been to one LAN event so far, and it’s great. I think the flight case might actually be easier to carry than hefting a heavy backpack: the handles are sturdy and comfortable, and it has chunky wheels for pulling it around. It’s also actually easier to get everything set up when you can see it all laid out in the flight case and pull out what you need, and then the case can be tucked away out the way for the duration of the event.

Recently-ish. It may or may not have taken me a few months to get around to writing this post. ↩︎
Using litres to measure computer cases always feels wrong. Those are the units we use for water. Don’t put them near the computers! ↩︎
The case also has holes to put security screws in to stop all of these nice easily removable parts from being removable. Very handy when you’re leaving it unattended at a LAN. ↩︎
Which for me means it was good fun for about an hour, and then I got fed up and just wanted it to be done already. ↩︎
Three months in and I still can’t remember these random strings of numbers. Someone even explained the versioning scheme to me. ↩︎
Along with a portable monitor, mouse, keyboard, headset, mouse mat, kensington lock, power supply, cables, and controller. It was a heavy bag. ↩︎

Further adventures in 3D printing

2024-08-04T00:00:00Z

The Bambu Labs P1S.

Not quite a year ago, I bought a Sovol SV06 3D printer and wrote about my initial experiences. At the end I joked:

I’m sure there will be more problems, but hopefully I get at least a week or so before anything else goes wrong. Maybe I’ll print an “X days since the last SV06 problem” counter…

That turned out to be more prophetic than I expected. It became a running joke that I’d flip the imaginary “days since” sign back to 0 almost every time I printed. I still really enjoyed having a printer, though: it’s so useful to be able to be able to go from an idea to a CAD drawing to a physical object in the space of minutes or hours. So when Bambu Labs reduced the price of the P1S — a printer generally regarded as about as trouble free as you can get — to £522 including shipping, I splurged on one.

Concerns

I make it sound like that was an easy decision, but I actually ummed and ahed a lot before pulling the trigger. I had a lot of objections to a Bambu Labs printer, and wasn’t quite sure if the price made up for them.

The Bambu Labs printers are designed to be more consumer friendly than most previous 3D printers. You can start a model printing directly from their website or mobile app, which employs a cloud-based slicer that then sends the model down to your printer. This is one of those things that sounds amazing for consumers, but should terrify anyone who works with computers. There are so many ways for a “cloud-connected” printer to go wrong, and with such potentially disastrous results it gives me anxiety just thinking about it.

This is not just theoretical, either. In a blog post with the rather under-stated title of “Initial Investigation in the Bambu Cloud Temporary Outage”, Bambu describe how a server-side error caused printers to start printing unprompted. Users on Reddit reported printers starting in the middle of the night, trying to print on top of other objects that were left on the build plate, and so on. 3D printers can easily start fires; having them cloud controlled is frankly insane.

As a result of that “temporary outage”, Bambu further improved the “LAN mode” for their printers, which allows you to sever its connection from their servers and control it over the network. That’s basically how my old printer worked anyway, so I was happy enough that I could enable LAN mode and ignore all the cloud nonsense.

My other objection to Bambu was more nebulous. Almost all 3D printers are built upon open source software, and some companies like Prusa go out of their way to make their products more open to give back to the community. Bambu don’t really do any of that: I’d be very surprised if they hadn’t incorporated a bunch of open source software into their printers and just ignored the licences¹. I’d much rather give my money to a company doing good, but the only equivalent printer was the Prusa MK4 which was double the price and didn’t come with an enclosure. To add an enclosure kit would have made it £800 more expensive than the P1S, and I just can’t justify that.

Experience

The initial setup of the P1S was a breeze. While the SV06 shipped in parts, the P1S came fully assembled and just needed some packaging and retaining screws removed. These were all clearly marked with large coloured arrows. It’s very much designed so anyone can do it.

I ran through the initial calibration, firmware update, and then put it in LAN mode. Then I just started printing and it went fine. No messing around levelling a bed, or using a sheet of paper to try and set the Z-offset properly; it just worked. It was really loud though. After talking a bit with a friend who’d also bought a P1S, I realised that most of his noise was from the fans, while most of mine was from the servos. A bit of research later and I found out they added servo noise compensation in a firmware update, but I hadn’t run the calibration for it because the initial calibration happened before the update. After doing that, the printer went from sounding like it was impersonating a continental police siren to just being a bit fan-y.

The biggest difference over the SV06 is the speed. I’d swapped the nozzle on the SV06 to a 0.6mm one, and generally printed at a layer height of 0.4mm. The P1S still has its 0.4mm nozzle, and I mostly print at a layer height of 0.2mm. So it’s laying down twice the number of layers, with a nozzle that can extrude half the amount of plastic… And it’s at least twice as fast! Prints that I previously wouldn’t have even attempted on the SV06 are now 8-10 hours on the P1S, without even adjusting the speed or lowering the quality. Here’s a side-by-side comparison:

P1S vs SV06.

The P1S can print eight objects because of its slightly larger bed, while the SV06 can only manage three. The P1S is also printing at a much higher quality. Yet somehow it still ends up being faster. It’s mind blowing.

The other big difference I’ve not mentioned yet is that the P1S is a “core XY” printer rather than a “bed slinger”. That means in order to move along the Y-axis (from the front of the bed to the back), the P1S moves the extruder while the SV06 moves the bed. This makes a big difference when printing tall objects, as they’re far more likely to wobble and come loose when the bed is moving back and forth. It also presumably makes the kinematics a lot easier as the mass of the moving parts is constant, instead of gradually becoming heavier as more and more plastic gets added.

The only failures

I’ve only had a handful of failures since getting the P1S. I had one weird issue where the slicer decided to print some parts extremely slowly, and the print just didn’t work out in those parts; that’s more of a slicer issue, though: after tweaking the model to stop the weird behaviour it printed fine.

The only failure I can directly attribute to the printer was when I tried ironing. This is a process where after printing the top layer, the printer slowly goes back over it at the same height while extruding a small amount of plastic. This is meant to fill in the small gaps between extrusions and give a smooth finish. In my case, though, it just clogged the nozzle and extruder.

At first I thought it was because I was printing too hot: the profile I was using was designed for fast printing, so had to melt the filament rapidly, but there was no way to turn that temperature down just for the ironing pass. I tried another run at a lower temperature and everything clogged again. I then swore off ironing, did a normal print, and everything clogged once more.

At this point I was getting exceedingly good at disassembling the hot end, but also fairly annoyed. It felt like I was using an SV06 again²! I’d previously read some recommendations that you should leave the door or top of the enclosure open when printing PLA, but had never really had any issues so hadn’t bothered. I tried a print with the top propped open and everything worked smoothly again. In hindsight all these clogging issues happened when it was particularly hot and humid outside, which was probably a factor.

Summary

Upgrading to the P1S has made the 3D printer feel more like a tool and less like an additional ongoing project. The speed increase continues to amaze me, as does the increase in quality.

I still think it was valuable to have the SV06 to learn how printers work — you definitely don’t get as much of that from using something so consumer-focused as the P1S — and figure out if I was actually going to use it long-term or whether it was just a fad for me. So it served its purpose, but I’m rather glad to see the back of it in favour of something better in pretty much every way.

And if they did there’s nothing anyone can do about it because copyright doesn’t exist in the same way in China. ↩︎
Although taking apart the P1S (which is a proprietary machine you might not expect to be very user-servicable) was orders of magnitude easier than taking apart the SV06 (which was an open source design). Everything is just much nicer: the connectors are easier to attach and detach, the screws are all a consistent size instead of needing a whole suite of allen keys, and so on. ↩︎

Project log: Filament weight display

2023-12-03T00:00:00Z

The finished project

One problem¹ I have when 3D printing is that it’s hard to gauge whether there’s enough filament left on a roll to complete a print. Sometimes it’s obvious when the print is small or the roll is full, but often it’s not. If I’m unsure about it, I end up obsessing over the printer instead of just leaving it to do its thing.

The typical approach to this problem is to use a run-out sensor, which stops the printer when it detects that the filament is no longer running through it. I’d rather know in advance though: it’s no good stopping the print if I’m making something that has to look nice and now half of it is one colour and the remainder will be something else.

While browsing around for ideas, I came across a project that used a load cell to measure the weight of the filament roll². I didn’t really know what a load cell was, but decided to do some research and see if I could build my own. I didn’t actually read the article I found, intending to figure things out on my own if I could.

Load Cells 101

A load cell, its amplifier, and some random headers

At the heart of the project is a load cell. It turns out these are the things that do the lifting in most electronic scales. They’re basically a carefully machined metal bar with a strain gauge attached to it. The strain gauge is a long trace of conductive material that runs back and forth across the middle of the bar. When the bar bends very slightly (due to load), the conductor flexes with it and gets longer or shorter; that flex changes its resistance by a tiny amount, which can be measured using a Wheatstone bridge.

The Wheatstone bridge is a diamond of resistors, and requires an ’excitation’ voltage to be applied across it in one direction, and the resistance is then read from the perpendicular pair. As the resistance is tiny, and the changes even more tiny, you generally need an amplifier to read it and output something more useful. The HX711 is such an amplifier, and is so ubiquitous that most places that sell load cells will just bundle one with it.

The HX711 connects to the load cell using four wires: two for the excitation voltage, and two for the output. On the other end it takes a 5V input, ground, and then has two pins to deal with the onward communication: one for a clock signal, and one for data. We’ll get back to that later!

Early prototyping

The prototype, mid-debugging

I decided early on to base the project around an RP2040-based board, as I had previous experience with them and they’re cheap and easy to get hold of. I started off with a Raspberry Pi Pico, slotted it into a breadboard, and connected it to the HX711. A short search produced three or so different python libraries, but I couldn’t get any of them to work reliably.

If you look at the picture of the prototype, you’ll notice a large bundle of wires to the left. These are connected to a logic analyser I bought to try and understand what on earth was happening, because it seemed like the code should work, and there was definitely some communication with the HX711 happening, but none of the readings made any sense.

At one point I noticed that moving my head near to the Pico caused the readings to change, but I didn’t understand the implication of that³. I went to bed unable to figure out what was going on, and just before I dozed off realised that I must have the pins configured wrong. The next day I checked the spec sheet and discovered that the pin with the number “1” silk-screened next to it is in fact GPIO 0, not GPIO 1⁴. The pin the Pico was trying to read data from wasn’t actually connected to anything, which is why waving my hand near it was enough to induce a signal.

Updating the code to use the correct pins made everything work much better and I started to get sensible readings. At this point I came across the RP2040-Zero by Waveshare, which is not only a smaller, cuter, cheaper Pico, but has silk-screened numbers that actually match the GPIO pin numbers (plus an actual a reset button!). I immediately bought several, and switched the prototype over as soon as they arrived.

The rest of the prototyping was reasonably uneventful. I used a little OLED screen I had sitting around from a past Ali Express order, and once again there were several python libraries to handle it. Soon enough I had raw weight readings from the load cell (which was stuck to my desk with painters’ tape) being displayed on the screen.

The load cells don’t measure absolute weight, so you have to “calibrate” them by remembering the reading when there is no load, and then applying a scaling factor to turn the raw reading into a weight. I worked these out by putting a known weight on the business end of the load cell, and then hard-coding the numbers.

An interruption to deal with interrupts

One thing I noticed with the MicroPython libraries for the HX711 is that they relied on polling the data pin to see if there was any data to read. The way the HX711 communicates is by pulling the data line low when it has data; you then have to pulse the clock line to get it to shift a bit of the reading out over the data line. The HX711 I have operates at 10Hz by default⁵, and reading the data takes almost no time at all, so the most “efficient” thing to do is to sleep for 100ms between readings.

This is fine if you’re not doing anything else, but gets awkward if you also want to refresh a screen at certain points, or check for button inputs, etc. It also upset me to see the data line being low for so long when viewing the logic analyser traces. The RP2040 supports setting interrupts on the GPIO pins, but I couldn’t find anyone who was actually using them for the HX711.

I therefore did the only sensible thing: wrote my own library, using interrupts to monitor for data availability. It was pretty straightforward, but didn’t actually work consistently. Looking more closely at the other libraries, they all do something to try to increase the speed at which the clock signals are written⁶: some were disabling interrupts, others were using assembly. I, again, did the only sensible thing: I threw all the python away and wrote a new driver in TinyGo.

My new code is event driven: it adds interrupts for button presses, and one for the HX711 data line. When the data line is pulled low, it removes that interrupt (so it doesn’t fire for every bit of data we receive), does the reading logic, then re-adds the interrupt. Theoretically if you spam buttons at an inopportune time you could mess up a reading, but the reading 100ms after would be fine. So my code spends most of the time idle, which translates to very little power draw.

User experience

While prototyping I was using some standard small push buttons to navigate the user interface I was creating. I soon realised that if I needed to enter weights on the real device I wasn’t going to be happy poking an annoying little button hundreds of times, and I didn’t feel like coding anything more elaborate to make input easier. Instead, I switched to using a rotary encoder. This is a bit like a variable resistor, but it can rotate completely freely, and sends a signal when it’s turned. It also has a button built in, so you can press it down to select things.

It took me a while to get the hang of the rotary encoder: it has two data pins for turning, and you have to wait for a falling edge on one pin and then immediately read the other to figure out which way it’s turning. My initial attempts at doing this weren’t quite immediate enough⁷, so I ended up with somewhat random data. Trying to select a number when going right sometimes increases it and sometimes decreases it is an exercise in frustration.

The correctly functioning rotary encoder makes it much easier to input numbers and change settings. I ended up with a very simple menu system at the bottom of the screen which lets you cycle between three options: setting the spool weight, zeroing the scale, and calibrating it. Zeroing is the most straightforward option: it simply reads the current value, and saves it as the zero offset in the flash memory. Selecting spool weight enters a mode where turning the rotary encoder increases or decreases the spool weight by a gram at a time; pressing the encoder in saves the value to flash and exits the mode⁸.

Calibration is a bit more confusing. Changing the spool weight changes the value you see on the screen directly and predictably. Calibration instead affects the “scale” value you can’t actually see; you just see the effect of the scaling on the weight reading. Still, if you have a known weight on the scale you simply rotate the encoder until the right weight is displayed on the screen. Pressing the encoder saves the value to flash as with the other modes.

Putting it together

The final assembly

The final step was to assemble everything in a way where it would be usable, and wires wouldn’t keep falling out whenever you looked at it. I found some cute little prototype boards that would just about fit all the components on – I left the OLED screen and rotary encoder off so they could be mounted to the front of the box.

I obviously 3D printed the enclosure, because I own a 3D printer and therefore spend a lot of my time 3D printing parts for my 3D printer. In my first prototype I put raised areas on the back panel and put some heat-press inserts in them, intending to screw down the protoboard. The screw holes I was going to use, however, were underneath the soldered-down RP2040-Zero and HX711. I instead uninserted the inserts and simply put some screws through the back panel with the intention of slotting nuts under the components. This turned out to be both incredibly annoying and entirely unnecessary; the board sits at the back of the box on its own, and there’s no real danger from it having a bit of freedom.

While I was prototyping I was powering the circuit from the USB port on the microcontroller, but for the actual unit I added a buck converter and ran a cable from the 3D printer’s power supply (which outputs 24V). This has the handy side effect of turning the scale on and off with the printer. I’ve recently bought a bench power supply, which made testing this part a lot easier: being able to dial in a voltage and current limit and then just plug things in is great.

The other thing that needed to change between my prototype and the final version was the load cell. It needed to be attached to the printer in such a way that one end bore all the weight of the spool (and, you know, not stuck to my desk with painters’ tape). I was originally going to do something fancy with bearings, but settled on the easier option of a spool holder which uses the same threading as the original, so it slots straight in:

The load cell mounted as part of a spool holder on the printer.

With all of this done, I invented a complicated mounting system to keep it attached to the printer. Any resemblance to blue painters’ tape is entirely coincidental.

Bill of materials and sources

Here are the major components that I ended up using:

Part	Source	Cost
RP2040-Zero microcontroller	WaveShare	£3.15
5KG load cell + HX711	AliExpress	£1.89
Buck converter	AliExpress	£0.51
SH1106 OLED module	AliExpress	£1.70
Rotary encoder	AliExpress	£0.80
Mini PCB prototype board	Amazon	£1.49

Where things come in packs of more than one, I’ve listed the cost of one unit. I’ve not included things like wires, connectors, or the filament used in printing the enclosure as you can use whatever you have to hand.

The source code I wrote is available on GitHub, and the designs for the 3D printed parts are shared in OnShape.

Among many, many others, of course. ↩︎
I can’t actually find where I saw this original project now, but there are quite a few kicking around if you search. ↩︎
This happened at about 1am and I was tired and frustrated. That’s my excuse, anyway. ↩︎
At this point I realised I’d made the exact same mistake the last time I used a Pico. Fool me once, etc. ↩︎
You can change this to 80Hz by resoldering a resistor on the board, but 10Hz is already several orders of magnitude faster than I actually need. ↩︎
If the clock signal stays high for longer than 60ms it’s treated as a shutdown signal by the HX711. This is somewhat unideal when you’re trying to read data from it. ↩︎
Because of my very clever interrupt system. I wanted to do as little work in the interrupt handler as possible, so I was just enqueuing an event to be processed in the main loop. This introduced enough delay that I wasn’t reading the second pin at the right time. The solution was to read the pin in the interrupt handler and then just enqueue a “left” or “right” event instead of my original “turning somehow, you figure it out” event. ↩︎
I was initially planning on hard-coding the weights for all the spools I’m likely to use, and just having a way to switch between them. But the thought of having to re-flash the device every time I bought a new type of filament made me reconsider. Plus, it was way easier to not do that. ↩︎

Adventures in 3D printing

2023-09-17T00:00:00Z

The Sovol SV06.

I’d been idly considering getting a 3D printer for a while, but have only recently taken the plunge. I picked up a Sovol SV06 from Amazon for £199.99¹, which is a model commonly recommended for beginners. About three weeks later, I think I’ve finally finished fixing all the problems the printer has, and thought I’d document them.

Setup and out of the box performance

The setup of the printer itself was straight forward. Most parts are assembled, you just have to bolt the frame together, bolt the various parts to the frame, and connect some wires. The hex bits in the iFixit Mako Bit Set were a godsend for this, as the included hex keys were a bit flimsy.

Once everything is bolted and connected, you turn it on and immediately start looking around for the jet engine you can hear. The fans are loud. The instructions walk you through the initial calibration, which consists of:

Levelling the X-Axis gantry (where the print head moves). The printer does this by (gently) ramming the gantry up as far as it will go.
Adjusting the Z-offset of the print head. The printer has an inductive proximity sensor attached to the extruder, but it doesn’t know how high it is relative to the nozzle. The calibration process involves manually dialing in this offset while moving a piece of paper back and forth under the nozzle.
Levelling the bed. This is entirely automatic: the printer just probes a bunch of points on the bed with the proximity sensor and builds up a mesh it can use to compensate for the bed not being level.

After that’s done, the included SD card has the standard “Benchy” model on it, pre-sliced and ready to print. It came out looking good:

A nice, problem free Benchy. No dramatic irony here.

The noise. Oh god, the noise.

I set about printing a few more things, but the noise of the machine quickly got to me. It sits approximately 80cm from my ear, and between the fans and the noises it makes when moving it was driving me mad. The fan in the PSU seems to sit at 100% power regardless of temperature or load, and sounds about three times louder than my laptop’s fans do when they’re running at full tilt. Fortunately, someone had designed a printable PSU fan silencer that redirects the airflow (and most of the noise) from the fan. It doesn’t feel like it should help that much, but it does significantly reduce the noise as it claims. This was the first of many times I’d use the 3D printer to print parts for itself.

The other noise was a lot less straightforward. The linear rods that all three axes run on pass through several bearings. Sovol apparently don’t bother to apply any lubrication to these, so it sounds like an elephant is moving through a gravel pit when the printer is running. Some people online suggest rubbing lube on the rods and pushing the movable parts back and forth, but this just results in a load of lube caught on the dust filters of the bearings².

The solution to this, then, was to dismantle most of the printer to gain access to each of the ten bearings, and manually lubricate them. This was tedious and messy, but not actually that difficult. It doesn’t seem like the kind of thing you should have to do on a brand-new machine, but I guess you get what you pay for.

Speeeeeeed

3D printers are slow. The SV06 is not one of the faster ones. One simple way to increase the print speed is to change out the nozzle. The SV06 comes with a 0.4mm nozzle, which is pretty standard, but if you upgrade to a 0.6mm nozzle you can extrude more than twice the volume of plastic in the same amount of time³. The consensus among anonymous internet people is that if you’re using a modern slicer there isn’t much difference in print quality when doing this.

I dutifully ordered a new nozzle, and after it turned up set about installing it. This is mostly straight forward, aside from the complication that you’re meant to do it when the hot-end is hot. That makes sense: you want it be under the same thermal expansion it will be under during use, but the tool they provide to change the nozzle is all metal. So you have a relatively delicate operation that you have to do in a bit of a rush before the heat creeps all the way up to your hand.

With the new nozzle in place, the printer was noticeably faster. I didn’t notice any difference in print quality, either.

SD cards are not fun

Up until this point, my process for printing anything was to slice it on the computer, export the gcode file to an SD card, turn around and walk over to the printer, insert the SD card, and start the print from the LCD. I don’t particularly mind those steps, but the SD card slot on the Sovol is terrible. It doesn’t line up well to the hole in the case, doesn’t guide the card in well, and is all round a pain to use.⁴

To remove the sneaker-net element of this process, I ordered a Raspberry Pi and installed OctoPrint on it. OctoPrint provides a web interface to the printer (which it controls over USB), and most slicers can automatically export the gcode to an OctoPrint instance.

While OctoPrint itself is great, there was one small problem: if you connect anything to the USB port on the printer, it tries to draw 5V from it and “backpower” itself. It’s not meant to draw power from the USB port, it’s just not designed well. A lot of the cheaper 3D printers share this flaw, it seems. The fix here is to get a power blocker such as the one made by PortaPow that simply leaves the +5V line unconnected between the two ends. Presumably Sovol could fix this by adding a diode to the USB power line, but maybe that would push their costs too high?

After getting OctoPrint working, I printed a nice case for it to mount on the side of the printer. I slotted the Pi in, and when I powered it on again it didn’t boot. When I went to pick it up to debug the problem, I burnt my finger on the SD card⁵. Apparently if you break SD cards in a certain way, they can short out and get very hot. Fun! Maybe I shouldn’t have been using the no-brand card that came with the printer…

What do we do with a drunken bed?

I continued printing bits and bobs, but was starting to notice a new issue: if I was printing multiple copies of the same object, those on the right hand side of the bed often failed. OctoPrint has a nifty plugin that lets you cancel certain regions from the build, which saves it ruining everything, but only being able to print in certain places was annoying.

I ran through all the troubleshooting steps I could think of, including a foray into custom firmware with different bed levelling abilities, but nothing seemed to help. Another OctoPrint plugin later and I could see the problem:

This should probably be straight.

The orientation of the graphic is a bit confusing, but you can see how the right hand side of the bed is significantly higher than the left. There’s a total variance of just over 0.5mm, which is apparently enough to cause problems even with the auto bed levelling. I spoke to Sovol support, and eventually they suggested disassembling the print bed and measuring the aluminium spacers that hold the bed. Sure enough, they were all different heights:

You had one job…

There’s a 0.13mm variance in their heights, which doesn’t account for the 0.5mm seen in the bed mesh, but it’s a good starting point. Rather than go back and forth with Sovol support over the course of many days, I just ordered some nylock nuts and reinstalled the bed without spacers. The nuts hold the bed in place, while still allowing you to tighten or loosen the screws to adjust the height.

After five or six rounds of totally and utterly uneventful adjusting and re-leveling, I got to this point:

This is much more straight.

There’s only so much you can do when you only have five screws to adjust, but I’m pretty happy the variance is now under 0.15mm. That’s definitely in the “good enough” range that the bed leveling algorithm can compensate for.

Whoops

So, about that “totally and utterly uneventful adjusting” I did. To get at the screws that hold the bed in place, you have to remove the thin sheet that acts as the build surface. This attaches magnetically to the bed, so it’s easy to do, but I am lazy and decided to leave it off while I fiddled with the bed.

There’s a slight problem here, though: when it’s working out the bed mesh the printer uses the inductive proximity sensor. The inductive proximity sensor detects metal. The metal is in the removable sheet. The first time I tried to run the bed mesh, the printer rammed the extruder assembly into the bed at a decent speed and ended up at a rather nasty angle.

I checked over the extruder and found the heat break had bent:

This should also probably be straight.

I tried printing with it as-is, but the filament came out too thin and at an angle, which made the print go about as well as you’d expect. I ordered a replacement, installed it, and… nothing worked still.

At this point I was getting thoroughly fed up. There seemed to be one problem after another, and no good way to diagnose problems with the print not sticking (because there are a dozen or so different potential causes). After a lot of frustrated googling, I found a post on the Prusa forums that suggested cleaning the build sheet with dish soap. I’d cleaned it with IPA, but several people were saying that dish soap magically fixed issues that IPA couldn’t. I took the plate to the kitchen, gave it a wash, and the next print went down perfectly.

Growing a backbone

For a blissful period of about four days the printer was chugging along perfectly with no issues. Then it started making a weird noise. In a display of amazing restraint, I didn’t immediately throw the whole thing out the window. Looking at the printer, I could see that the cable running from the extruder assembly to the main board was sagging and rubbing on top of the print as the print head was moving around. I’m not sure what property of the cable was keeping it aloft before, but it apparently ran out after about three weeks.

Like most of the other problems with the SV06, this design flaw has been noted by others and worked around. I printed a cable chain and installed it⁶. Amusingly, while I was printing the chain, the cable dragged on the print and dislodged one of the pieces entirely before it was finished. Fortunately, it didn’t affect the neighbouring pieces, so I just had to run off a replacement for that one.

The difference is rather pronounced:

It feels like I own a 3D printer to print parts for my 3D printer…

If you can’t see it: in the first image the cable is sagging and actually ends up below the print bed. The individual links of the cable chain limit its freedom of movement, stopping it sagging.

The end?

Once again the printer is printing properly again. I’m sure there will be more problems, but hopefully I get at least a week or so before anything else goes wrong. Maybe I’ll print an “X days since the last SV06 problem” counter…

I think, if I had to do this all again, but with the knowledge I have now, I’d have stumped up the extra cash to get a Prusa MK3S+⁷. This is the original machine on which the SV06 (and a lot of other cheap imitations) is based. Some obvious benefits it has over the SV06:

The extruder cable runs on the outside of the machine, so won’t droop onto prints
The heated bed has copper embedded in it for use in the induction sensor, so it won’t crash into the bed if the build sheet is removed
They actually put lubricant in the bearings instead of shipping them bone dry
The bed is held in place with screws instead of poorly sized aluminium spacers, so you can adjust the height without having to take the whole thing apart
They don’t use the cheapest possible power supply and main board, so it doesn’t backpower off of USB devices or have the loudest fans known to mankind

Prusa also have a much better attitude towards 3D printing: they open source the hardware designs (which is why there are so many cheap clones), and they actually use the printers themselves. The plastic parts of an SV06 are injection moulded, but those on a Prusa printer are actually printed on a Prusa printer. Not only is it cool that they use their own products, it means they have to run them en-masse so they’re obviously invested in making them reliable. They also have a reputation for exceptional support.

Despite all the problems, I do enjoy having the printer. I’ll probably talk more about the prints I’ve done that weren’t for the 3D printer itself in the future.

The RRP is £279.99, Amazon discounted it down to £269.99 then offered a £70 voucher. The voucher says it expires at midnight, but it’s said that every day for the past three weeks… ↩︎
Which is exactly what another set of people said would happen. It was worth a try, though. ↩︎
This feels strange, but if you work out the areas of the nozzles it makes sense: a 0.4mm diameter nozzle has an area of 0.04πmm² (the radius is half the diameter, and the area of a circle is πr²), and a 0.6mm diameter nozzle has an area of 0.09πmm². Maths! ↩︎
At least it doesn’t eject the SD card across the room like this Ender 3 V2! ↩︎
My only 3D printer related injury so far. It’s impressive I can be around a 200 degree hot-end and somehow burn myself on a storage device. ↩︎
Well actually I printed 5 copies of their calibration piece until it was perfect, then printed the actual cable chain, then had to sand each of the individual links because they still weren’t good enough. God, I hate sanding. ↩︎
Or maybe I’d cave and get the newer, shinier, much more expensive MK4. That wouldn’t be out of character. No, I didn’t just check my bank balance. You’re imagining things. ↩︎