'Tenet' project start

12 Jul 2022

categories: small-computers
tags: rpi

I’ve had an idea kicking around for a while, to make a raspberry-pi-based netbook. Two years ago I was playing around with thermal receipt printers for another project idea and I was also starting to learn stenography. I got the idea to build a netbook for stenography. Some kind of steno netbook. I’ve taken to calling it tenet.

I regained interest in the idea when I saw the ShaRPiKeebo on CrowdSupply. This powerful little device has a fantastic screen. I got to see one up close recently when a friend showed me her new Playdate console. I’m not particularly keen on the keyboard the ShaRPiKeebo comes with, but it’s so close to my use case that I bought a couple of the PCBs and backed the project. In the meantime, I also picked up some of the screens on breakout boards from Adafruit!

So, what’s the use-case, what’s the pitch? I want this computer to be small, portable, solar-rechargeable, and daylight-readable. It’s for writing and light programming away from a desk, possibly even off the grid. It could be used in a pinch for sysadmin/on-call tasks, or some kind of terminal-based email or chat, but its main use case is for writing. Am I a writer? Do I know what writers want? Why am I asking myself so many questions instead of building small computers?

Image: a bunch of computer parts, loosely arranged. Read below images for more descriptions

Ok, what about components?

Image: A Keyboardio Atreus keyboard. 44 keys arranged in a split-monoblock, columnar orthogonal layout.

The keyboard I’m starting with is the Keyboardio Atreus. It is small, thin, light, and a little more ergonomic than other 40% boards. I say “starting with” because it has a couple of shortcomings for this project: it won’t work for a full steno machine because it would need one extra column on the right side, and for more weight and space savings I should use a board with Choc switches and keycaps. But the Keyboardio Atreus is more than up to the task of being the board for the prototype computer.

Image: A 2.7-inch 400x240 SHARP Memory Display, on an Adafruit breakout board. Shown here with a Raspberry Pi 4 for scale.

The other part tied for first place in user interaction is the screen. These Adafruit SHARP Memory Displays are 2.7" on the diagonal, and have 400x240 pixels. The display is monochrome, with no back- or front-lighting. They communicate with the Pi over I2C, so some custom software will be necessary to use them as a monitor.

Image: A 3-cell lithium ion polymer battery, connected to a circuit board that’s hooked up to a small solar panel.

Powering it all is a 3.7V battery from Adafruit. I’m not sure it’ll suffice for the printer but we’ll get to that shortly. I’ve got this hooked up to a circuit that accepts DC power from a solar panel or USB-C power. I have no idea how long the thing will last on a single charge. I guess once I get it running we’ll find out.

Image: Two thermal receipt printers, one in a blocky enclosure and the other cut apart, to become longer but less thick.

The icing on top will be a thermal receipt printer. I hope that this could operate in a few modes. The first is standard, to tell the computer to print a file, and have it come out the top. The second would be to have the terminal print its buffer line-by-line as it scrolls above the top of the screen. This second use case is challenging to achieve, but fulfills the destiny of this modern-day typewriter.

Image: An alternate view of the receipt printers, showing how the long thin one uses part of its original enclosure.

I’m not sure yet which shape of printer will be best for the computer as a whole. Honestly it will probably have to come with its own supplemental power supply too, because these need 6-9V to print reliably. Lots of experimenting with shapes to do. Which brings me to the next component: the enclosure.

Image: All of the above parts, stacked as densely as possible.

My first idea for an enclosure was a kind of backwards laptop: when closed the printer and screen would lie flat, above the Raspberry Pi and battery cells.

Image: The same as above, but now a hand is holding the screen and long/thin printer angled up 80 degrees from horizontal

Upon extending the hinge, the printer and screen come up. It was my first idea about what this should look like. I was hoping to evoke something of a spiral-bound memo pad that flips open in a similar way.

Image: The above parts, this time using the bulkier printer, arranged in a cube-like shape with the screen forming an angled face at the front.

Once I had all the parts together on the table (notably the bulky battery cell), I found another arrangement that’s a little less complicated, as it has no moving parts and does not require redesigning the printer’s enclosure. Is it sufficient for the computer? Is it better? Nobody knows the answer.

As I write this, my ShaRPiKeebo PCBs are on their way here from France. I have a few ideas on how to experiment with the Adafruit boards to make those displays work, and I have some CAD work to do to get these parts to stick together more permanently.

Yours in Unnecessary Small Computers,
Spencer