Meet Project Patchouli, an open-source drawing tablet project to 'build your own tablet from scratch'
For something intended to mimic good old pencil and paper, drawing tablets and the tech behind them are surprisingly complicated. If you fancy a crash course in how they work and want to build your own from scratch, I have the open-source project for you.
Project Patchouli from designer Yukidama is a project to "build your own EMR tablet from scratch". As helpfully laid out in Yukidama's YouTube video, an EMR tablet is one that uses Electromagnetic Resonance that sends a signal to a tablet, which is then translated by the tablet. It's a quick and responsive bit of technology, but different pen vendors work off different frequencies, which can impact compatibility.
The video shows how electromagnetic pencils have coils and capacitors near the tip; a test board picks up that frequency and uses a signal amplifier to send that information to a computer. With an oscilloscope, Yukidama measures the frequency of each pencil as it touches the board, and then that frequency as they press harder. Two different pens register two different frequencies.
This project uses a smart array of coils in the tablet itself, making it "compatible with most commercial pens from different vendors, offering an ultra-low-latency pen input experience for your customized hardware projects."
Admittedly, due to the high level of complexity in the build, some of this project goes over my head, but the gitlab source gives the firmware and hardware designs you need to build it. It also provides helpful graphs and some extra pictures in the 'docs' section.
Much of the hardware blueprints are in CAD files, which means (for most) having to send those files off to get created by a circuit board manufacturer. A project like this won't be done on a whim, but it's still rather impressive.
Over on the Project Patchouli Discord, Yukidama has said that they are looking into documentation so that the non-initiated can also replicate the project and has said, "Please let me know if there's something you want to know in particular, so I can include them in the guide." Though I'm tempted to say 'well, all of it', I do think the YouTube video does a good job at explaining the background of EMR tech and why artists use EMR tablets.
In a sense, one could look at this more as a proof of concept than a replacement for a drawing tablet. Modern drawing tablets will have all kinds of neat software and hardware handshakes like tilt control or high-pressure sensitivity, and they will be a good bit bigger than the rather small tablet Yukidama is using. But what makes it interesting is that the tech is there and ready to use. It being open-source allows someone else to pick up the project and run with it.
Still, if you have the will to make one, and don't mind contacting a PCB manufacturer of some kind, this not only seems like a solid way of getting around pencil compatibility issues but also a way of learning about tech that you may not have put much thought into until now, I know It's certainly made me a little more appreciative of drawing tablets.