[R] Redesign options

A project log for Tetrinsic [gd0041]

A motorised, pressure sensitive and haptic feedback slide encoder.

kelvinAkelvinA 08/11/2022 at 15:080 Comments

Redesign requirements

So I'm changing from a dual-action to a triple-action switch since there's more space. This reduces the length the fingers move from 30mm to 24mm, but I'm thinking of going with a "rounded" 25mm. The mental compute of accurately moving my fingers to 5 positions exceeds having to think of an extra actuation layer, especially because the layers are discrete but the location on the key is continuous. Additionally, this means that instead of 11^3 - 1 combinations, Tetent will have 13^3 - 1 combinations, which is 65% more chord combinations, and the max and min button zones being closer means that all chords are easier to key. A while ago, I was thinking of having a 6th button in the columns for a potentially better use with non-english languages, but this solution achieves that in a better way.

The project might become the "TeTriad Switches", but for now, I think "TeTwin" looks better.

The thumb keys would also benefit from this, since I've been missing the ability to do a "shift last" ("aB") or "space inbetween" ("a b") in my mental simulations. With the dual-action, I just had "Ab", "AB", " ab" and "ab " available.

Redesign options

I've been researching capacitive touch sensors as an option. They're manufacturable from a PCB fabricator and I hear that they can sense proximity if the sensitivity is high enough. I need to accurately detect 5mm from the surface, but only need to detect a single finger in 1 axis, so perhaps it's possible. 

I don't think an IR based solution is going to work outdoors.

I've also been looking for small resistive touchscreens to no success. However, I have just found these 1.14" screens.

I've only been able to find <0.96" and >1.3" screens mainly, with a few in the range that didn't quite have dimensions that would work. This screen would fit in nicely.

Ever since the first Tetent concept, I've wanted to put a screen under the keys for backlight animations, but the surface of the keys aren't visible when in use in any of the concepts so it hasn't been much of a priority; it'll be more like the glowing Apple logo on old MacBooks or, more recently, the Nothing Phone 1. 

It seems that, at this size, the power consumption is comparable to the same size of OLED. My hope was that there'd be a small screen with a resistive touch layer on it that I could use.

I don't think I'm going to be able to sense capacitiev proximity though that metal shield, but perhaps I can actually use it to my advantage and use it to detect subtle changes in capacitance across the area due to force applied on the screen. This could reduce noise and allow extra-long (5mm+) nails to work without loss of accuracy.