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lainchan archive - /diy/ - 2947

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_01: Watch and learn

I know absolutely nothing about assembling my own electronics, and next to nothing about the parts I'd need, but those seem like minor problems in the face of having to constantly compromise on buying or scrounging my own. Anything anyone else has made never seems to live up to specifications that I want or look for. This isn't a "how do I into electronics" or a "I'm such a cup of soykaf I wish I could be better", I'm gonna try to learn the basics myself and build up from there as independently as I can. Mostly I'm posting this so that I'll feel like randos on the web will hold me accountable if I end up doing jack-all with my newfound motivation. But if anyone was willing to share a design/build philosophy they stick to with their projects, it'd be nice to hear it. Whatever.

First project will be a digital wristwatch - nothing fancy or superhard I hope, but if it is, I intend to get my money's worth before throwing in the towel. I'm writing this at just past 1am. No idea what materials to use but ideas are floating around in my head and I think I have a rough idea of the basics. Since I'm starting essentially from scratch, I've got to research all kinds of soykaf. I'll update whenever with pics of this project as I go. Will also include my notes and thinking so anyone reading along can follow my rationale, or that's the idea. Plans are to turn this into a personal campaign of epic learning and win.

- tell time (fuarrrking duh)
- wearable in rain
- adjustable wristband/clock
- somewhat sturdy shell

- alarm?
- what else, it's a watch...

- ripstop nylon for the strap
- plastic/rubber/stainless steel adjustment (probably rubber)
- cubieboard/rpi/arduino for clock functions
- battery (replaceable or chargeable?)
- led screen module/failing that, basic pinpoint lights
- soldering iron, probably (I've no idea how to solder, better learn soon)
- plastic/metal casing
- glass/transparent plastic cover if led module doesn't have one already
- whatever's needed to waterproof this soykaf

TL;DR I'm gonna snort a line of knowledge and kick today in the dick. Here goes.

Signed, Calicat /01


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Use one of these bad boys - russian VFD. Maybe use Arduino uno as controller. To save power, add a button to turn display off.


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_01.1: Watch and learn

A few days of finding out what I need to know and additional research to see what I might be able to do realistically felt good. Felt good to have my spare time taken up by something semi-productive instead of the black hole of vidya. Decided on the main three components: display, power and controller, but the other materials will take more consideration

Parts list:
- 0.96" oled 2-part display
- cr2302 coin cell battery
- arduino gemma
- casing to be determined (dun dun dunnnn~)

Update notes:
- sticking with a 3v coin battery since gemma specs said something about absorbing 9mA while running (not sure what the time scale on that rate is but shouldn't matter much anyways)
- considering soldering in a rechargeable LIon battery as a backup power source
- alarm might not be possible without additional parts; will have to check out gemma's potential once it arrives
- parts won't be delivered for at least a week (_ _") but this means more time to research and think through designs
- still gotta learn to solder
- mentally filing away vacuum fluorescent display as a handy part for a desk/wall clock or similar project
- buttons? or will gemma need to be set externally?

TL;DR So far, so good... too bad the parts won't get here sooner.

Signed, Calicat /01.1


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It'd be a good idea to read through the datasheet for your battery - some things you may not have considered on it are the internal resistance (i.e. as you draw current from the cell the output voltage drops) and cell voltage drop as it discharges.

You seem a bit confused on current, too; amps are coulombs of charge per second, so the time period is 1s. And the draw of the 0.96" OLED is ~9mA; you're looking at roughly 18mA current draw total. Divide the mAh of the battery by the average current draw to get the rough lifetime in hours of the circuit. A CR2032 is 240mAh, so 13 hours at that draw optimistically assuming your display and uC will still run at the 2V level.

Remember to figure out timekeeping, too. Internal RC oscillators aren't close enough to keep time, so you need some form of external IC for it or to do it with a 32kHz crystal and loads of messing around with calibration.

You've picked a seriously challenging project (small space stuff is a nightmare at the hobbyist level - difficult to get the level of custom components big consumer electronics companies do) but you should learn a lot; good luck!

(personally I've always wanted to build a watch using a bubble seven segment display - none of the battery issues of a VFD but still retro!)


Hmm, hadn't considered those factors. Will probably order a breadboard to see how the parts I've ordered will interact; if they play nice (or nice enough to function as a basic prototype) then I'll move on to optimization.

RE difficulty, everything always turns out to be harder than I initially think but instead of giving up this time, I'll power through.

Thanks for the advice!


Yeah, breadboard first is a good idea - worthwhile just to get an idea of layout too. Some stripboard is good for semi-permanent prototypes/soldering practice too.

And as a minor thing, you could look at NATO straps - it's a nice standard for durable watch straps and plenty of variety.

Keep us updated!