Project Patchouli: Open-source electromagnetic drawing tablet hardware | Hacker News Reader

Project Patchouli: Open-source electromagnetic drawing tablet hardware

patchouli.readthedocs.io

461 pointsffin49 comments

As a software engineer, seeing hardware projects like this makes me want to go back to school and pick up a few electrical engineering courses. The hardware space just seems to unlock so much (honestly blown away with the LCD retrofit at the end of the video: https://www.youtube.com/watch?v=igVscvWAR1s )

I've played with simple electronics on the arduino and raspberry pi platforms but this is a whole new level. Anyone gone down this path? Something you would recommend?

Honestly, just pick up the Art of Electronics - Horowitz and Hill. Spend some time working through that book. By the end of it, you'll have a better grasp of electronics than 90% of the engineers I've worked with, all who are EE bachelors/majors. It's a 3 month job at most, less if you do a dedicated hour a night. Then pick up some breadboard and parts, and build to your hearts content.

Making a working circuit is honestly very easy once you know the basics. Look inside a Made in China knockoff appliance, and you'll see that most things can be made from a couple of conponents and a microcontroller. Pull apart an old TV remote or bluetooth device, and look up the part numbers and what they do. There's not much to it. You have to remember that most of the stuff getting designed and built in South East Asia is done by people with zero qualifications. Electronics being "the thing that smart university people do" in the West is mostly a mental block, culturally constructed because people don't want their kids getting electrocuted so bombard them with constant threat of death if playing with electricity (which mostly isn't a worry anymore unless you're working with mains power).

The true discipline of Electronic Engineering is designing something that works for every eventuality and environment, with close to 100% reliability, at the very cutting edge of what is possible with the components we can afford while balancing physical and financial constraints. That's something which takes years of both academic study and industrial experience.

"Art of Electronics - Horowitz and Hill."

very good recommendation, that book help me turn my studies in to reality

electronic circuit emulators will help with the basics as well (eg https://www.falstad.com/circuit/)

Note that AoE is not an academic book, more a book for tinkerers.

I'd recommend also to play with https://www.falstad.com/circuit/circuitjs.html

> Honestly, just pick up the Art of Electronics

I got this advice in 1998. I have the book. I found it useful for the "art" part. It got me through the projects that I was working on at the time, but personally it didn't help me with the fundamentals. Paraphrasing what has been said on this site many times in the past: AoE is a great first book in practical electronics if you already have an undergraduate degree in physics. I showed my brother AoE when he was building guitar pedals and he couldn't make sense of it and said it was obviously assuming things that he didn't know (he had no high-school science background).

There are a lot of potential and/or assumed pre-requistites even for basic electronics: high school physics, first-year calculus, maybe a differential equations course, certainly familiarity with complex numbers. As I understand it EEs take vector calculus and classical electromagnetism, that's a long road for self-study. For that reason it's hard to give general advice about where to begin.

For someone starting out I think the first things to study are DC and then AC analysis of passive circuits (networks of resistors, capacitors, inductors), starting with networks of resistors. Ohms Law, what current and voltage actually mean, some basic introduction to the physics passive components. This is the basics, and I don't see AoE getting anyone over this hump. This could be learnt in many ways, electronics technicians and amateur radio people know this stuff -- there are no doubt courses outside university both on line and in person. If we're talking books, get a second hand copy of Grob's "Basic Electronics." Once that's covered you can move on to semiconductors. I can recommend Malvino's "Electronic Principles," but this book won't teach you about resistors, capacitors and inductors. After that I think the Art of Electronics would be approachable. And also more specialised topics like digital design or operational amplifier circuits.

A book that usually gets a mention is Paul Scherz "Practical Electronics for Inventors." I got that book later, I personally found it a bit overwhelming with the mixture of really basic practical stuff combined with more advanced circuit theory, but it's no doubt popular for a reason.

Another standard recommendation is to buy one ARRL Handbook from each decade (I have 1988), the older ones have less advanced (hence more accessible) material. But reading the "Electronics Fundamentals" chapter is no substitute for Grob and Malvino.

Seconding an old ARRL handbook.

Personally I preferred Boylestad as well as Sedra & Smith.

Boylestad was an excellent first look at electronics with S&S being great for going in-depth on some topics.

there's a few youtube channels that are nice to watch to get you more interested in electronics, my two favourite are:

Bigclivedotcom (nice, basic fun) : https://www.youtube.com/@bigclivedotcom/videos

Mend it Mark (more advanced) :https://www.youtube.com/@MendItMark/videos

I want to add that Moritz Klein's DIY synthesizer videos are top notch, especially for beginners in electronics. As somebody who is just working through AoE it feels like a great compliment and is very satisfying.

I’m going to go against the standard advice of this book or that course.

Pick up (broken) equipment and start disassembling it to figure out how they turn A into B [1]. Go down the rabbit hole of hunting down the service manual of the thing or one of its siblings. Look at how the pcbs follow the same pattern in competing design. Look at how all the yamaha, sony, medion, … amplifier/tuners are made in the same way and learn from it. Notice that one that is costlier and has those few quircks in its design. Notice how different variations of a theme achieve the same result, but died out because the tech doesn’t scale or simply proved to be suboptimal. Try to repair your broken equipment by understanding the path that the signals and power lines follow.

Rinse and repeat a few years and you’ll get a grasp on what the innards of an unknown electronic thing looks like without opening it. Then open it and be amazed that there was a different, cheaper, simpler way to turn A into B.

All along the way you’ll experience that most educational resources aren’t actually that good at explaining, or that they follow a different school of mathematical notation, or that they’re really good at explaining this detail but the rest is missing.

Design your own pcbs. Remember that - like software - hardware design is iterative. Remember that - unlike software - hardware iterations cost money.

Hope this helps.

[1] the ways to turn A into B are rather limited and it relies heavily on electromagnetism and conservation of energy.

I think you can take a bit more directed approach too.

You can build a micro-controller with a circuit that controls a stepper motor. Let the motor do something simple/fun. Connect the fun doohikie to give feedback to the microcontroller — e.g. using some kind of an encoder chip that converts motor's rotation amount to numbers that will tell the microcontroller how much to move, initialize the doohikie's start state.

But you can understand a lot more if you don't use the HBridge chip for the motor. Build the bridge circuit yourself. Build your own power supply for the microcontroller too(if you want to).

You can pick a path to go down on and focus on specific parts:

1. For the h bridge there is lots to learn. Designing the operational amp for D2A conversion as well as amplification/signal modeling — which you will need for the motor for current limiting in the h bridge per motor spec for the doohickie you want to power — That will teach you quite a bit about analog electronics and design. What kind of currents you need to protect and how e.g. using opto electronics. Limiting noise from power supply and parasitic noise so that your circuit does not misfire. You will likely need a set up of an oscilloscope, soldering irons and breadboards to prototype. Learn some basics from a book about design then go back to the circuit and build.

2. If you build your own PCB for this. It is a multi month project. You can learn a out CAD and chip layout. But I think you can do this in parts for example you can design the initial PCB only for the digital components and then connect it to a breadboard where you can prototype the H bridge you want.

3. If you choose to learn digital design and embedded system programming then maybe you can build the tougher analog parts for motor control using store-bought components and chips and focus mostly on the programming the microcontroller. That is a totally legitimate part too. You could use an old MCS-51 microcontroller and learn about data and program memory addressing and interrupt handling from scratch.

Forty years ago, I was on my way to college to get a computer engineering degree. I had already been programming in 6502 assembly language and was frustrated that I didn’t understand the hardware side of things as much as I understood the software side of things. Best decision I made. It allowed me to view computation as something more abstract. The barrier between hardware and software processing is artificial and can be moved one way or the other. What is CPU microcode, for instance, hardware or software? It’s really low level software that is typically burned into a ROM but is also sometimes downloaded. Even if you decide to stay with software as your primary day to day job, you’ll be comfortable talking to engineers on the other side of the line and that will help inform your understanding of what’s possible, how much it will cost to design and ship it, how long it will take, and how it will perform.

Before you dive too deep, check what's already available and let your tinker TODAY without having to solder anything. You can still do so, even design PCB and get them mailed to you (like I did, it's fun) but honestly spend a bit of time (and money) on CrowdSupply to see the plethora of fun and useful OSHW out there. IMHO only after having considered what's beyond the usual consumer electronics it is worth learning to build, not before.

Is there any prototyping software you'd recommend that could do this? I'd like to play with this stuff virtually without having to spend meatspace time/money.

Ah, funnily enough I'm a prototypist software by trade... but I have NO idea about that, none. Honestly you can find emulator, simulators, etc but typically those devices precisely only make sense because the emulated equivalents do not. For example I just received a DeepDeck ... it's "just" a macropad, so basically a glorified partial keyboard. It's OSHW and open source so you "could" run the Web stack locally to "configure" it ... and yet you'll never know what it "feels" like to turn a physical knob in order to navigate between browser tabs. You can imagine doing it ... but it's still quite different.

Anyway there are plenty of things like https://wokwi.com and it's fun ... but it's NOT like the actual hardware. Most of those projects precisely make sense because of the tangible aspect, or because you support a "vision" (e.g. Precursor) and learn while tinkering with them.

So... no unfortunately sorry I don't have any recommendation for doing this virtually. Maybe it exists but I'd caution against thinking it's equivalent.

I found that programming concepts map really well to digital electronics. The objects in your object oriented language are real objects with their own internal physical state. A large fraction of what embedded engineers do is just APIs and protocols.

Controversial opinion but you do not need to learn electronics to have a good time. One can have plenty of fun simply writing software and plugging prebuilt modules together on a breadboard. Ohm and Maxwell need not apply.

https://en.touhouwiki.net/wiki/Patchouli_Knowledge

And then yeah he's playing a Touhou rearrangement in the project intro video. "Original: ZUN".

I wholeheartedly support weebs who create useful open-source electronics and share them with the world.

I'm always happy when I see Touhou mentioned on HN. It's reasonably popular with a certain subset of hacker types that grew up in in the 2000s

The Youtube introduction video (https://www.youtube.com/watch?v=igVscvWAR1s) is a great explanation of the tech and the end where he retrofits it into a Panasonic CF RZ is wild.

The production quality of this video is almost too good to be true! Kudos to Yukidama!

Isn't this technique encumbered by patents? Or have they expired?

Anyway I'd be interested in the implementation of a 3D mouse also.

Wacoms key patents did expire which is why there's such strong competition in the tablet space now, and why prices have fallen through the floor.

I wonder why Apple still uses active pens on the iPad when passive EMR has become such a commodity. Maybe it's just rent-seeking, a passive pen would probably be much easier to clone without paying Apples MFi fees.

I think there’s also latency issues and some features possible with the active pen that wouldn’t be with passive technology, although I don’t know for sure.

because they didn't make it, of course.

Some of Wacom's tablets can be used with both the pen or with your finger (acting like a touchpad).

Anyone have any idea whether the touchpad part could be made open-source? Or even some closed sourced off-the-shelf solution that could be integrated with the above?

EDIT: There is a Canadian company that has recently released an open source trackpad called the Ploopy Trackpad [1].

[1] https://github.com/ploopyco/trackpad https://ploopy.co/trackpad/

As an aside, anyone here uses drawing tablets for work? I got a cheap Wacom tablets and found it super useful, for sketching ideas or understanding something before starting to implement new code.

I am doing exactly the same, also writing down some raw ideas I have in it to not forget them.

Yes.

I've dreamed of using a stylus and tablet since reading _The Mote in God's Eye_ when I was young, and have preferred to use them since using a "Koalapad" attached to a Commodore 64 in the school computer lab when I was young.

The NCR-3125 I had was donated to The Smithsonian by the guy I sold it to, along w/ a lot of other materials on pen computing --- PenPoint was my favourite OS alongside NeXTstep, and the high-watermark of my computing experience was using the NCR running PenPoint as a portable, then cabling it up to my NeXT Cube to transfer data --- had a Wacom ArtZ attached to the Cube, so still had a stylus, just it wasn't a screen.

Futurewave Smartsketch is still my favourite drawing program, and I was very glad that its drawing system made its way through Flash and into Freehand/MX (which I still use by preference and despair of replacing). If you have a graphics tablet, be sure to try out:

https://www.wickeditor.com/#/

Hopefully the folks making Graphite will figure out that it's a core functionality for a drawing program to work w/ a graphics tablet --- haven't been able to do anything when I've tried.

I sketch (either on a Samsung Galaxy Note 10+ or Kindle Scribe or Wacom One or Samsung Galaxy Book 3 Pro 360), take notes (mostly on the Scribe), do block-programming (Wacom One or Book 3), or draw (on the Book 3).

For the last few years, I have been using small Wacom Intuos S tablets as a replacement for mice, trackballs or touchpads.

I configure the tablets in the "Relative" mode, in which they behave exactly like a mouse, unlike in their default "Absolute" mode. I configure left click to be done by touching the tablet with the stylus and the 2 buttons that are on the stylus to generate right click and double left click.

The advantage over a mouse or trackball is the much more comfortable position of the hand and also the much higher speed and accuracy of positioning. Moving the pointer to any location on the screen is instantaneous and without any effort, due the lightness of the stylus and to the lack of contact with the tablet.

Because the stylus is extremely light, I can touch type on the keyboard while still keeping the stylus between my fingers. This allows faster transitions between keyboard and graphic pointer than with a standard mouse (because the time needed to grip the mouse is eliminated). Only when I type longer texts, I drop the stylus on the tablet.

The tablet is no bigger than a traditional mouse pad, so it does not need a bigger space on the desk.

After switching to use exclusively a graphic tablet, I would never want to use again a mouse, trackball, trackpoint or touchpad. I only regret that I have never thought earlier to try this.

Besides being a better mouse than a mouse, a tablet obviously allows to do things for which a mouse is inappropriate, e.g. drawing or handwriting (e.g. for signing a document).

I should mention that I have always used the Wacom tablets with Linux. I have never tried them on Windows, so I do not know if there they work as well.

This is pretty cool! Never considered this

Yes, but Wacom recently discontinued macOS driver support for older versions of the Intuos, and I had to downgrade to an older driver to make it work.

When it doesn’t anymore I’ll need to get something else, probably an iPad so I can also use it as a 2nd screen.

In case you need alternative to the official driver, https://opentabletdriver.net/ is a well maintained driver.

Possibly not the use-case you're thinking of, but I've been using a Wacom Intuos tablet as a mouse replacement for a few years now on MacOS and on Linux. I use it in pen mode (where the area of the tablet maps to the screen) - you can also configure it in mouse mode (like a touchpad, where the movement is relative to where the cursor is on the screen) which should work better with multi-display setups, though it's not to my preference. I have my pen/stylus setup so that tapping it onto the tablet acts as a left/primary click, the larger button on the pen is right click, and holding the smaller button and dragging on the tablet is scroll/pan).

MacOS is well-supported once the drivers are installed, though sometimes the driver doesn't seem to pick up tablet (either after the laptop or tablet goes to sleep). Restarting the driver fixes this, though this bug seems to have been fixed in the latest driver release. Linux works out of the box (at least on KDE/Arch), though sadly customization support on Wayland isn't quite there yet compared with what you could do on X11 (with the xsetwacom utility). For drawing support though it should work perfectly but as far as I know you can't the the button functionality, which is a bummer when using it as a pointing device.

The main benefit for me is that it feels much more ergonomic compared with a regular mouse or even a vertical mouse or trackball and I don't get anywhere near as much wrist or shoulder pain - especially in the cold temps in the middle of winter where I am. There is a bit of an adjustment period and I find for interacting with small UI elements such as buttons it can be a bit tricky, but for me the benefits outweigh the downsides. The only other downside I can think of is that when using the tablet over bluetooth (wired is also an option and tracks a little more smoothly) the battery only lasts 1½ days compared with the weeks/months a wireless mouse would go for.

I'm an artist and haven't used a mouse since somewhere in the 00's when I developed some RSI in my index finger while working in the Flash animation mines.

Annoyances: games that require you to push the cursor against the edge of the screen to move the view, app/website developers who force tiny scrollbars that constantly hide themselves despite me setting the OS to never hide scrollbars, having to restart the tablet drivers most of the time when I move between having the laptop docked with the big screen and big tablet on the desk, and taking it out to a cafe or the park and using the smaller tablet that lives in my laptop bag.

Beautiful! Added to list of projects! Retrofit into screen of old 27» 2009 imac that is run by a raspberry and drived by a screen driver.

This seems very similar to another open-source tablet effort, which went a step further and designed a Hall effect sensor-based tablet: https://github.com/pompyboard/pompyboard

The creator of it has showcased the prototype at an osu!* streamer's channel (since low-latency absolute positioning devices are highly desired for playing osu!): https://www.youtube.com/watch?v=v1afJ7OpacU

* that is osu! (sic) rhythm game, not to be confused with OSU universities

Has it actually reached properly functional state?

The showcase video didn't look very convincing and neither website nor the discord channel contained a lot more information. Although I didn't dig through discord history too carefully.

It's one thing to hook up 200 hall effect sensors to a MCU, and read few of them or send data over HID at 8000Hz. It's different thing to read all 200 at 8000Hz and figure out the position with reasonable resolution and accuracy.

Can it also detect the exact moment pen touches tablet or additional button clicks? Or does it require taping keyboard with other hand? Which is probably fine for OSU, but less so for drawing.

Regarding the last point, pompyboard is very much a tablet or pointing device meant only for enthusiast osu! players from what I understand. No artist in the world needs a 8KHz polling rate tablet let alone 1KHz. Tablets from other brands are much better suited for drawing. While the basic idea of a rectangle you put a pen on is the same for artists and osu! players, the more detailed requirements are basically opposites

Basically:

- Pen click is useless for osu! or can just be digital, while artists would want analog pressure

- Buttons on a pen are actively detrimental for osu! but very useful for artists

- Smoothing on a tablet is more detrimental for osu! the more of it there is but absolutely necessary for artists

- High polling rate is useless for artists (they would have input delay due to the smoothing they need either way) but very useful for osu!

- Big tablets are useless for osu! players as they typically only use a 5-15cm area while they are very useful for artists

I think the entire point of something like pompyboard is to make a tablet just for osu!, which doesn’t exist right now. Meanwhile for artists there is already a whole industry of tablets available for them

I love the cute diagrams in the `Scan Rate Optimization` section.

Very well written reverse engineering documents.

This is such a great project! I want one!

Someone donate to this guy so he can upgrade his 20 y/o Thinkpad!

Awesome

Why negative points. Can I not say I'm happy he or she made this project. It's not for the internet. It's for the content poster only I wrote that I liked it. At that time I was the only poster. I didn't write first! I wrote awesome. Because I liked it. Don't assume that everything is for you the reader to read and not the poster to read

I use a pen tablet daily for many years it's very very close to my heart and my work. Don't just assume sarcasm where it is none. Not everyone shares the same culture. Also why should I write a long swan song when a simple awesome is accurate and conveys everything I wanted to say

You could have expressed that with a upvote.

Text comments here are supposed to have more content. (And lamenting about downvotes has a high chance of getting more downvotes)

Comments should add something worthwhile to the discussion. Redundant comments ("noise") tend to be downvoted. (I didn't downvote you!)

If you meant for the comment to be read by the content poster, then something more meaningful than a single-word response would have been more appropriate.

These are the rules and practices which have kept HN lean and functional over nearly two decades.

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