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A project log for Tetent Timespy [gd0136]

A wearable PDA / smartwatch with a Tetent [gd0090] based input layout.

kelvinAkelvinA 08/08/2022 at 21:530 Comments

Idea 1

Currently stetching a concept idea for the project thumbnail. My first-thought idea was an L like shape, but I don't think clothing would work that well around it and I don't think the keyboard would be in a good location. This is my first sketched idea.

The screen is on the outer face of that 6mm thick section and the Tetent keyboard is in the 19mm section. Unfortunately, the entire width of the watch is way out of bounds. 

Tetwin Switches

I've turned to #TeTwin Switches [gd0041] to see if I can reduce its height. Now that I know that the distance between columns needed is more like 21mm instead of 17mm, I can remove the 2mm dowels from the top of the 2 keycap sections.

I have a feeling that I'd be using M3 screws or 3mm dowels instead of 2mm due to better availability at the >35mm lengths the design calls for. Ideally, the M3s would actually be on the outside and hook the main key on both sides:

A shorter key both helps with this project and #Tetent Tiny [gd0040], as well as fitting the thumb keys next to the finger keys for all #Tetent [gd0090] projects. It seems that the tallest key is 16.95mm, so including things like the PCB, it's likely to fall in the 19-20mm range anyway.

Idea 2

So this idea includes the eliptical shape of my arm 80mm from the wrist, as well as a location for the thumb buttons. However, those thumb buttons increase the thickness of the section above the arm to 21mm and the large curve means that there isn't even 35mm of space for the screen.

Specification considerations


It seems that the only location a solution won't immediately fail is if the keyboard is on the top of the arm. Any other side is too thick. When my fingers are bent, the distance between them is more like 19.5mm and not 21mm. The new Tetwin design seems tolerant to such a change. Then there's the rotation of the forearm that further complicates things. Tetent having such a small window of comfortable configurations really doesn't help; perhaps the thumb column would have to be ommited since it's what's causing the ergonomic issues (just like in all Tetent projects at the moment, now that I think about it). I only need the first two:

I actually have only now realised that the keymap only calls for 4 buttons and not 5. Anyway, I think the plan is to remove the bottom two and just have 2 extra long switches. This may solve a few issues across the whole Tetent lineup since I don't have to get the thumb in a position to press a <6mm long keycap whilst not pressing the ones around it. It also greatly simplifies the mental compute, resulting in lower intent-to-keypress latency. It's also more straightforward knowing that Ctrl, Alt and Win are toggle modifiers instead of just Win being a toggle and having to do some fancy, potentially 2 handed work with Ctrl and Alt.


It seems that the side of my arm is still the optimal viewing angle for the screen and use of the keyboard. How bendable are standard OLED's anyway? Anyway, it looks like the keyboard would make the outer length >80mm so the OLED I found in the previous log is out. If the watch is going to be large, it should at least be large and sleek and without relatively thick bezels, and the 2.69 inch display would need bezels over 13mm in size.

I actually thought the bezels on the LEM-T / TICWRIS MAX were exaggerated to be small, but they are actually some very thin bezels IRL.

I've found this OLED display that I originally dismissed because it's 80.5mm in length.

The overall size of the Timespy would then be something like 84.5mm across the arm and 51mm down its thickness. The thickness should actually fit no issue, and if I have another 6mm of arm space to spare, I could go for a 3.5" screen.
I assume that the 3.5" is a portrait display and the 3.26" is a landscape one. It's slightly cheaper (£5 after VAT) , slightly larger, needs slightly fewer pixels driven and with the large thumb keys, the Timespy would likely need to be 90mm anyway for ergonomics.

Battery, motherboard, speaker and joysticks

Right, so Tetent takes up a considerable amount of space already so I'm not all that hopeful.

It turns out that a) my design has come right back to the original L shape I was thinking of and b) that there's enough space for a 18650 cell. I wanted to have a removable battery but wasn't sure how it was going to happen, so this is good news. 

It seems that the joysticks used in #Tetent Turntable [gd0038] could be small enough to implement into the design.

The reason why I haven't been able to merge Tetent and Turntable into one is because the only solution I could compute involved having to rotate to get the joysticks under the fingers. I don't think the same issue would happen in this configuration.

The speaker(s) is likely to be an afterthought, but I might be able to fit these somewhere:

The motherboard is likely going to be CM4 compatible but use the CB1 I got for £9 avg since I have 4 of them and 2 have been reserved for #SecSavr Suspense [gd0105]. Even at the standard £21.60 price of the CB1, it's still cheaper than all the other options that only have half the RAM.

The thickness of the CB1 is 4mm. I'll assume the PCB is an additional millimetre.

Idea 3

Thus from the research above, this is my 3rd idea:

Computation and research time: Approx 8 hours.

Published: 04:02 @ 9th Aug