3 ms·
Mobile phones and digital cameras etc often come with USB cables for charging. The intent is that they be charged from the ports on a computer but there's no re
by tb 17y ago
Mobile phones and digital cameras etc often come with USB cables for charging. The intent is that they be charged from the ports on a computer but there's no reason they can't be charged directly from a socket. The exception is the iPhone, some versions of which will not draw any current from the USB socket until a handshake protocol with the PC is complete, and so they will not charge from this kind of arrangement.
- bedris 17y agoMy BlackBerry is the same way; it will only draw current from the USB socket if it detects the requisite software installed on the computer.
- allenbrunson 17y agomy iPhone came with a little transformer that plugs into the wall for charging. obviously there isn't going to be any handshaking there. i was under the impression that all iPhones were like that. are you saying that some aren't?
- ssharp 17y agoMy iPhone charges from the home adapter that came with the phone, of course. I also have a 3rd party USB charger that I bought two or three years ago for my iPod. It came with both a home adapter and car adapter. The car adapter will charge my iPhone but the home adapter won't.
- rufo 17y agoYour home adapter probably uses the old FireWire power pins, which the iPhone 3G can no longer charge from. There is also a handshake, but that's separate and (as of the 3GS) only displays a "product not designed for iPhone" warning - even if it displays the warning, it still lets you use the device.
- mikepurvis 17y agoI don't believe it's malicious—the "handshake" is just the device requesting that the USB port switch to high-power mode. The line is always 5V, but the device needs to request to draw anything more than 0.1A. In the case of wall-transformers for iPods, phones, etc, they're either using an unstandardized handshake (such as the phone shorting its two data lines, which can be recognized by the transformer with just a relay), or they provide power all the time, which could damage a low-power device that was inadvertently plugged in.