1. For Tetrinsic, I'm planning to integrate Bluetooth, which will allow for satisfyingly wireless communication with no extra PCBs, for only a small BOM increase.
2. I forgot that #T^2 TyMist [gd0138] is no longer happening due to optical constraints, so audio output is once again required... maybe. Planning to use a mono Samsung speaker (which I mentioned in a TyMist log) for now and potentially add 2 smaller stereo tweeters if the MVP works (and it even makes sense to go stereo).
3. Where is that speaker going? Where the 26650 was. It's much better to go with the 10Ah dual battery I sourced for an older TimerSpy concept. Why should Tetent have less capacity than 2 TimerSpys? 
4. If I don't put a speaker there, Tetent might shrink 26mm, but it does seem like 210mm is ergonomically valid wheras shorter (like 190mm) could be uncomfortable for wrists. Actually, the speaker is only 15mm wide, so I could add it and still go down to a 200mm solution, which is probably the sweet spot between ergonomics and portability.

I've also got to research what I'm going to do about the charging circuity. 10Ah will take half an eon to charge at the typical 0.1A found in development boards. The most ideal solution would be to charge from the 30W SuperDart Realme charger, but I think 15W is a more reasonable goal to aim for. At that wattage, I should have a full charge in 3 hours.

[22 March] Tetent is now down to 204mm long, which makes it shorter than an A5 notebook. I've also determined the main speaker location:

It's here so that it doesn't interfere with the otherwise symmetrical design on the back, and because I imagine that this side would be facing up if the device is momentarily put down on a surface and facing towards the user in 1-handed mode. 

There's just enough space for a 357090 5Ah battery on each side, so this controller is going to be a dense fit almost as if I was Apple and managed to get custom components that use all the available area. 

I'm expecting Tetent to be 700g or less, assuming that 

• Batteries: 130g
• Tetrinsic: 40g x 8 = 320g
• Speaker: approx 100g
• Case and other components: approx 100g