Lessons Learned While Building A DIY Pen Plotter

There was a time when plotters were the pinnacle of computer graphics output. While they aren’t as common as they used to be, there are some advantages to having a plotter. [Symon] wanted a plotter and decided to make one from scratch. Truthfully, he wants to build a CNC machine, so the plotter is just a stepping stone. In fact, some of it may be a little much for just a plotter. Other design choices have worked for the plotter, but don’t look like they will work well for the eventual CNC design.

As an example, the plotter uses 2020 extrusions and lead screws. An Arduino with a CNC shield provides the brains. GRBL, of course, runs on the Arduino, so the whole machine runs fine with normal G-code. This post will be especially interesting if you want to build a plotter or something similar. We especially like that it covers the design rationale for each choice made It is great to learn from others successes and, of course, their mistakes.

If you really want just a plotter, you don’t have to spend much. You can even go super minimal if you want.

Bleep Remover Censors Those **** Bleeps

One of the more interesting cultural phenomena is the ‘bleep’ that replaces certain words in broadcasts, something primarily observed in the US. Although ostensibly applied to prevent susceptible minds from being exposed to the unspeakable horrors of naughty words, the applied 1 kHz censoring tone is decidedly loud and obnoxious enough that its entertainment level falls somewhere between ‘truck backing up’ and ‘loud claxon in busy traffic’. There is thus a definite argument to be made to censor the censoring beep to preserve one’s sanity, which is the goal of [Oona Räisänen]’s Bleep-be-gone project on GitHub.

Using a Perl-based wrapper, the versatile ffmpeg framework is used to filter a provided video that was afflicted with bleepitus, before outputting a pristine version where the infernal noise is replaced with blissful silence. This use of silence for censoring naughty words is incidentally becoming more commonplace over an ear-piercing beep, but a tool like Bleep-be-gone can be used to hasten the demise of its terror. Considering that the point of the 1 kHz back-up alarm beep is to draw a person’s attention to a piece of heavy equipment moving about, there is clearly no good reason why the replacement of a naughty word should warrant a similar drawing of attention.

Using 5V Programmable Logic Here In The 2020s

Do you speak GAL? [Peterzieba] does, and has pulled together a collection of documents and tools so that you can too. There’s a dividing line in electronic engineering education, between those who were taught about FPGAs, and those who weren’t. Blurring that line slightly is gate array logic (GAL). These devices were a preceursor to the FPGA, with a much simpler structure, and usually in those days UV-erasable in the same manner as an EPROM. And oddly enough, they, or at least their successor compatible parts, are still available, and as handy DIP devices that talk to 5 volt logic.

The guide goes into detail about the parts, the terminology surrounding them, and the CUPL language which raises a few memories for us. There are several possible workflows, including for those not faint of heart, the possibility of writing a fusemap by hand. We’re impressed by that one.

If these devices interest you, our colleague Bil Herd wrote a two-part guide (part one, and part two) which should answer your questions.

Thanks [Bjonnh] for the tip!

Featured image: “Commodore Amiga 1000 – sub board – Texas Instruments PAL16L8ACN-0126” by Raimond Spekking

One-String, One-Trick Pony Plays “the Lick”

Wouldn’t you love to be able to play a song on a stringed instrument even though you don’t have an iota of musical talent? That’s the idea behind Strumli, a single-string instrument built by [Factorem] that plays “the lick”. You know, the lick. Chances are, you’ve heard it somewhere before.

Essentially, it’s a pill-shaped bowl with a soundboard. A high-E guitar string is wound around bearings and tuned with a guitar tuner. The lengths of string between the bearings correspond to each note in the lick. Strum it in the right direction, and Bob’s your uncle.

So how the heck did [Factorem] come up with the proper string lengths needed to play the song? After a bit of fancy math involving the equation that represents the relationship between the measurable frequency of a vibrating string under tension and the tension itself, [Factorem] had the overall length of the string. Then it was a matter of finding the frequencies needed to play the lick, along with their corresponding lengths.

Since the string exerts about 80 pounds of tension across the 3D-printed soundboard, some serious internal bracing is required, which [Factorem] figured out in CAD program. All the files are available if you want to build your own. Be sure to check out the build/demo after the break.

Would you rather just build a little harp? Here’s the inspiration for Strumli — a single-string number with a full octave.

Continue reading “One-String, One-Trick Pony Plays “the Lick””

2023 Halloween Hackfest: Flickering Pumpkin Pin Is Solidly Built

Now first of all, [Steph] grants that you can already take your pick of several LED pumpkin badges out there on IO. That’s not the point. The point is that this flickering pumpkin pin is nicely-built as well as being open source.

Even though it’s fully featured — it flickers, it’s wearable, and it’s lightweight — the build couldn’t be more simple. It’s fancy through-hole LEDs and a coin cell holder, plus a tack pin to stick it through your shirt. But the final result is quite elegant thanks to clever use of PCB layering.

The first version was to get all the layers right to let the light through and embellish the jack-o-lantern’s lines with manufacturer-applied silver solder, but as [Steph] points out, it looked ‘like something a disturbed child might carve into their desk in detention’. So [Steph] enlisted [Mx. Jack Nelson], who improved the artwork.

Pretty much every component does double duty here, including the tack pin — it serves as a switch because it can hold the battery in place. The battery’s edges reflect the glowing light quite nicely around the edge of the pin. And the LEDs beneath the battery prevent it from slipping out. You can see how it goes together in the video after the break.

Continue reading “2023 Halloween Hackfest: Flickering Pumpkin Pin Is Solidly Built”

LittleFS: The Emphasis Is On Little

It used to be that developing for microcontrollers was relatively relaxing. These days, even a cheap micro like the Raspberry Pi Pico has multiple cores, networking (for the W, at least), and file systems. Just like desktop computers. Sort of. I found out about the “sort of” part a few weeks ago when I decided to embark on a little historical project. I wanted a file system with a large file that emulates a disk drive. The Pico supports LittleFS, and I figured that would be the easy thing to do. Turns out the Little in LittleFS might be more literal than you think. On the plus side, I did manage to get things working, but it took a… well — dare I say hack? — to make it all work.


I’m an unabashed fan of the RCA 1802 CPU, which is, of course, distinctly retro. The problem is, I keep losing my old computers to moves, natural disasters, and whatnot. I’ve had several machines over the years, but they seem to be a favorite target of Murphy’s law for me. I do currently have a small piece of hardware called an Elf Membership Card (by [Lee Hart]), but it lacks fancy features like disk drives, and while it could be expanded, there’s something charming about its current small size. So that led me to repurpose a 6502 emulator for the KIM-1 to act like an 1802 instead. This is even less capable than the membership card, so it was sort of a toy. But I always thought I should upgrade the Arduino inside the emulator to a processor with more memory, and that’s what I did.

I started out with a Blackpill STM32F board and called the project 1802Black. The code is a little messy since it started out as [Oscar’s] KimUNO code, and then my updates layered with new updates. Also, for now, I shut off the hardware parts so it won’t use the KimUNO hardware — you only need a Blackpill (or a Pico, see below) and nothing else, although I may reenable the hardware integration later.

It wasn’t that hard to get it running with just more memory. Still, I wanted to run [Mike Riley’s] Elf/OS operating system and I also had a pair of Raspberry Pi Picos mocking me for not using them in a project yet. The chip has excellent Arduino board support. But what sealed the deal was noticing that you can partition the Pico’s flash drive to use some of it for your program and the rest for a file system. You can get other RP2040 dev boards with 16 MB of flash, which would let me have a nearly 15 MB “hard drive,” which would have been huge in the 1802’s day. Sounds simple. If it were, though, we wouldn’t be talking.

Continue reading “LittleFS: The Emphasis Is On Little”

Hackaday Prize 2023: The Wildcard Finalists Are Here

We’re in the endgame now — there’s just about a month to go before the final results are announced for the 2023 Hackaday Prize, which means all of our finalists are in a mad rush to put the finishing touches on their respective projects. Today, ten more hackers are about to feel the heat as we announce our final group of finalists from the Save the World Wildcard round.

As finalists, each of these projects has been awarded $500 to help further their development. But perhaps more importantly, they are now officially in the running for one of the final six awards, which includes the Grand Prize of $50,000 and a residency at the Supplyframe DesignLab.

Continue reading “Hackaday Prize 2023: The Wildcard Finalists Are Here”