Stupid USB question

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I have, in the last year, acquired a toothbrush, a Kindle and a phone all of  
which use mini (or maybe even micro) USB ports for charging and all say they  
can be connected via their supplied lead to a computer for charging.   In  
any case all the ports are identical.   I also acquired a mains powered  
charger for the Kindle.

I only actually need one lead don't I?
The mains charger will work for all 3 devices won't it?

It's so simple and obvious I find myself doubting the answer.  

Re: Stupid USB question

Graham Harrison wrote:
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Devices that charge from a +5V source, yes, they could charge
from a wall adapter which puts out +5V. On the face of it, it
seems a pretty simple problem and solution.


The complexity comes, from any products protected by their manufacturer,
to only work with the manufacturer's charger. For example, some Apple
stuff, looks for certain voltage levels on the D+ and D- pins of the USB

    VCC   <--- +5V source, suitable for charging.
    D+    \___ Normally only for data, but abuse-able for proprietary reasons
    D-    /
    GND        Electrical ground

So I can't guarantee that "X works with Y". It all depends on the generosity
of the manufacturer. For example, on a toothbrush, it wouldn't make much
sense to "protect" it so that only the official "Toothbrush Charger" would
work. But if they want to add cost to the toothbrush, by enforcing identity
info, they could.


Example of a smart consumer, building a device to fool an Apple product into
charging itself. Not all the components in this example, are for "fooling".
But the four resistors, set up as two voltage dividers and connected
to D+ and D-, are what the Apple product uses for "validating"
the charger.

Fortunately, it's not worse than that. They could have designed
chargers, with a serial bus protocol, to validate the equipment,
with public key encryption or the like.


I thought there were some development in the works, to cause cell phones
to have a common charger, but I don't know how that's going.

    "Geneva, 22 October 2009

     ITU has given its stamp of approval to an energy-efficient
     one-charger-fits-all new mobile phone solution."

So maybe, some day, there'll be fewer adapters around. And
fewer "schemes and scams". For example, if the toothbrush
said on the package "works with universal mobile phone charger",
that would be a start.


Re: Stupid USB question

On 4/4/2013 7:23 PM, Paul wrote:
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There is a standard for the resistor between D+ and D- to indicate the  
current. But it can even be more complicated than that. The phone and  
probably the Kindle should be designed for high current, but not all usb  
chargers can supply high current (1.5A to maybe 2A). The toothbrush is  
probably 0.5A. I never saw a USB tooth brush, but why not...

I would saw the smart power supplies capable of delivering high current  
will probably work fine for the tooth brush, but the phone and kindle  
should use proper power supplies.

There are a few webpages where people have tested "replacement"  
chargers. Amazing how few meet specifications.

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Re: Stupid USB question

miso wrote:
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It's amazing. I looked for a Kindle adapter here, and it
claims to supply up to 2.1 amps. And all through some kind of
USB plug.

( product link shortened)

Now, someone here, is working in the opposite direction. Using a USB power
source (laptop), to put power into a Kindle that has a barrel power connector.
And the claim is, the Kindle draws 1A while charging.

So this is very much a situation, where you'd be best advised
to research the exact model. As they probably all work differently.
The Kindle depicted in the previous link, apparently it "trickle
charges" off the USB power as a power source, versus fast charging
via the barrel power connector.

And the stupid Kindle manuals I could find, make no mention about
charging characteristics at all (no mention of current level,
power in operation, anything practical like that). So you'll have
to find a hardware hacker page, to get any tech info. I don't own a
Kindle here, so haven't a clue what they need.


Re: Stupid USB question

A lot of tablets use 2amp supplies on the microusb and can be charged  
faster with a different connector. [Phones these days are maybe 2AH, but  
tablet batteries are 5AH and up.]

If you can dig deep enough into the device OS, it will indicate the  
current flow. The device (phone, tablet, whatever) needs to monitor the  
charging current in order to determine when to stop charging the  
battery. [The fuel gauge needs to monitor the current used by the  
device.] The data is there. Getting it takes some effort to find the  
location/command etc.

In the dark ages (probably still true for notebooks), the keyboard  
controller, which itself is a uP, would have firmware to charge the  
battery. This was done for safety reasons, i.e. it would be a bad to get  
a virus that decides it is entertaining to blow up your battery.  
Firmware is firm! You can't touch it with a virus. [Apple was infamous  
for not using this technique. No problem if your software is good. Big  
problem if your software sucks, hence those macbooks that caught fire.]

Phone and tablets don't have a keyboard controller. [Even phones with  
keyboards seem to use the Arm CPU for decoding.] Now the charger might  
still be independent of the main CPU since it doesn't cost that much to  
make a smart charger. For one thing, the customer might remove Android  
and install linux, so you can't depend on the CPU doing the charging,  
though it could be in the bios.

Without turning everything into a research project, use the charger from  
the manufacturer, especially for tablets. Maybe less so for phones. But  
at least use a charger that actually came with a phone rather than a  
mystery charger. I have Android and Blackberry chargers, and they seem  
to work fine for phones. For tablet, I use the stock charger.

Note how the Monoprice charger was "ok". Looking at the trace itself, I  
think it is fine. Not as good as the rest, but good enough. The battery  
itself is a filter of sorts, so the supply can be a bit noisy.

If I had to describe Monoprice, it is a company that curates Chinese  
tech devices. They pick decent items for the price. Maybe not the best,  
but you won't get trash either. They used to do just cables, but nowaday  
they have more complex items. I heard a reviewer on a podcast indicate  
the Monoprice earbuds are decent. It doesn't surprise me that some  
company could evaluate the market, find the decent model, then get their  
name stamped on it. It really isn't a bad business model.

I won't say every cable I own is monoprice, but at least half of them  
are and I've never had a problem with them.

Re: Stupid USB question

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Maybe the question wasn't so stupid.   I think I'll continue to use the  
specific cables etc.   Thank you gentlemen.  

Re: Stupid USB question

It never occurred to me that anyone would sell a device that doesn't  
meet specifications, well because that is how I operate. [If you don't  
meet spec, you redesign.] But apparently some in China have a different  
attitude. Then again, I never expected horse meat in beef meatballs, and  
we can't blame China on that fiasco.

I noticed Monoprice has their name on the cable jacket, probably to keep  
the supplier from substituting a different cable.

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