Some notable models in the line-up of classic looking digital watches:
- Casio F-91W: $14 which gets you a basic watch
- Casio AE1200: $40, modern module with timezones, stopwatch, timer
- Casio G-Shock DW-5600: $50, Similar to AE1200 in functionality, adds shock-proofing
- Casio G-Shock GW-M5610: $110, Similar to DW-5600E but adds solar, radio time-sync
- Casio G-Shock GW-5000: $300, Similar to GW-M5610 but has a stainless steel case instead of plastic
- Casio G-Shock GMW-B5000: $400, Similar to GW-5000 but has a stainless steel bezel and bracelet
- Casio G-Shock GMW-B5000T: $1100+, Similar to GMW-B5000 but in titanium
Some comments on a great article from an EE who has many axes to grind about stupid old decoupling myths (which this article gets mostly right!):
> A related trick is to put ferrite beads on MCU output lines
You must be extremely, extremely careful with this. In general, ferrite beads are hard to apply correctly and great care is required if you want them to work out. Do it wrong and you'll probably be making things worse, instead of helping. See for example:
Honestly, the datasheets are usually just wrong. The writer is an intern and the material is cargo-cult copy-pasted. If it works it's by accident, or because it wasn't critical in the first place. Read the datasheet, understand what it's trying to do, then go ahead and achieve that end in the most sensible manner.
> It is true that at very high frequencies — hundreds of megahertz — the capacitor’s residual inductance becomes a limiting factor. At that point, combining multiple different capacitors can offer somewhat better wideband noise suppression.
Nope. It's still wrong and dumb to do this with MLCCs unless you have simulated the hell out of the whole thing. You should practically never parallel different values of MLCC. Instead follow EMC wizard Henry Ott's advice: pick the smallest package you're willing to deal with, then the largest capacitor you're willing to pay for in that package, and just use that everywhere. This is called "big V" decoupling by Ott and decoupling master Bruce Archambeault and it is not the best way to do things, but every better way is much, much, much harder to do. "Big V" will work for everything that doesn't involve underfilled BGAs, and even most of those.
> tantalum polymer
I actually kind of hate these guys, I don't find much use for them outside DC-DC converter output capacitors. They have too little ESR to damp things that need it, too much ESL for high frequency use, and are just too expensive for general use. They're not bad or anything, they just don't really have a sweet spot. MLCCs plus a few cheap high-ESR aluminum electrolytics (often found these days as the high-temp long-life parts) is a really effective combination. Maybe a few solid tantalums for intermediate bypass if appropriate.
> Y5V
Thank the heavens that these are basically extinct. Good riddance.
Okay, enough comments, you might then ask, how the hell do I decouple things in production designs?
First, put one bulk capacitor, minimum, on every rail. Aluminum electrolytic if the rail leaves the board ever, maybe tantalum if it doesn't (or maybe not, solid tantalums have... reputations). My go-to series is Rubycon YXM or YXJ for through-hole electrolytics, Nichicon UCB/UCW or Chemi-Con MLE/MLF for surface-mount, and AVX TAJ for tantalums. These can physically be located anywhere.
Then sprinkle down one 1uF 0402 per part for the small parts, or one per power pin for the big digital chips. Place these at the power pins, no exceptions. Things like MCU analog rails usually don't need ferrites but might get pi filter type structures. It depends on how important they are, really. If it's a big or dense board, toss in another tantalum or two physically near the chips or chip clusters to help keep the electrolytics honest.
You can decouple 500MHz processors and pass radiated EMC at Class B with this approach. It's not hard to do, it's cheap (but not cheapest, this isn't going to get you to Shenzhen-special COGS), and it works great.
PET is formed via the condensation of ethylene glycol (ethane-1,2-diol, aka EG) and terephthalic acid (1,4-benezenedicarbyoxylic acid, aka BDC). In the process, a proton (H, a hydrogen) is lost from the carboxylic acid (COOH -> COO) and a hydroxyl is lost from the alcohol (R-OH -> R). The H and OH combine to form a water (hence "condensation") and leave, and an ester bond (RCOO-R') is formed. Amide bonds (RCONR'), the backbone proteins and materials like Kevlar, spider silk, and Nylon, are similar, but less flexible and harder to break.
This condensation reaction (and others) is reversible. If you heat PET in boiling water, you can begin to depolymerize the polymer into its constituent monomers by having a water molecule consumed in the reaction (RCOOR' + H2O -> RCOOH + HO-R').
However, PET is a rigid plastic that acts as a barrier material (that's why it's used for bottles and packaging), and has a high glass transition temperature (the temperature at which polymer chain mobility becomes broadly possible -- the polymer is in equilibrium, while it is kinetically trapped below the Tg). This inhibits the breakdown of PET, particularly at low temperature.
Hence, the sentence from the abstract:
> With a high ratio of aromatic terephthalate units—which reduce chain mobility—PET is a polyester that is extremely difficult to hydrolyse.
Aromatic rings are just that -- rings. They don't flex a lot and can't undergo a lot of thermal motion, can't change conformation, etc.
> Here we describe an improved PET hydrolase that ultimately achieves, over 10 hours, a minimum of 90 per cent PET depolymerization into monomers, with a productivity of 16.7 grams of terephthalate per litre per hour (200 grams per kilogram of PET suspension, with an enzyme concentration of 3 milligrams per gram of PET).
> We also show that biologically recycled PET exhibiting the same properties as petrochemical PET can be produced from enzymatically depolymerized PET waste, before being processed into bottles, thereby contributing towards the concept of a circular PET economy.
So, they depolymerize the PET, an subsequently repolymerize the terephthalic acids to produce new PET. I haven't clicked through to find if they recycle the EG as well, though.
Usually you offer a connect button with the most popular providers. You could also detect a login with somename@whateverapplemaildomain in order to passthrough for those addresses. There are some discovery mechanisms that can be added for DNS/http(s) services as well against different tlds.
In the end, probably would just add an apple-logo button next to twitter, google and facebook auth buttons.
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Aside, in terms of data storage, separate the account, user and login/auth details. An account is related to activity inside the system. A user is a person authorized to use/act on or as that account. A login is an authority and related information to enter as a given user. Logins can be an OpenID reference, AD Integrated User, an API token, a local password entry (salted/hashed of course).
If you make the separations above, you'll have far fewer issues if/when you need to make your application more flexible in terms of users/authentication against accounts. It also is very helpful when you will have "individual" accounts and "business entity" accounts, which may have variances in UI/UX.
Beyond this, would separate the actual API/UI systems from auth systems relying on integrated tokens (like RSA signed JWT on an internal authority). In this way, your API systems only need to worry about "allowed" signers, and the roles assigned in the token's claims. Of course then there are issues with token lifetime, refresh and revocation to consider.
Sorry for the blathering on this, literally working on an authentication management system (fairly barebones initially) right now. MVP at end of day after 4 months work.
