Feb 102015
 

Recently I saw SONICable Indiegogo project promising to double the charging speed on computer. It is supposedly an advanced USB cable with a magic switch cutting your charge times in half. But not everything is as it seems.

First onto a topic of “unleashing double the charge power of the regular charge cable”. As you might know, USB standard limits current to any USB device at 500 mA. What is not obvious from this is that even now you can have devices pulling much more than this – all the way until small fuse stops you. Devices obeying the standard pull 500 mA because they are well behaving citizens – not because USB restricts them from more. Just measure current of any USB cup warmer. :)

Some devices, mobile phones in particular, also have a fast charging mode that triggers when they detect a wall charger. Detection method itself used to be different for every manufacturer. Fortunately they got standardized into two camps – Apple and everybody else. Leaving Apple aside, most phones use USB Battery Charging Specification. Deep in technical text there is a Dedicated Charging Port (DCP) detection method consisting of “short D+ to D- through resistance RDCP_DAT“. At end specification we have RDCP_DAT defined as maximum resistance of 200 Ω. In laymans terms – just connect the freaking D+ and D- wire together.

Since standard USB cable has four wires (5V, D-, D+, and GND – let’s forget about ID for now), whole high-tech solution is to connect two wires together. That will make device think it is connected to a wall charger and that it can stop being good 500 mA citizen. It is the phone who will then pull around 1000 mA (rarely more) from computer. Since fuses on USB port are intentionally overdimensioned, computer will generally allow it.

There are thousands of YouTube videos alone showing you how you can do this. All you need is to get an old USB cable and cut it open. Then short data wires (white and green) together and voila – you have a cable giving you 1000 mA magic.

There are devices enabling this on eBay. Quick Google search found me The Practical Meter and USB Meter Pro on Kickstarter using exactly the same “magic” as SONICable. Heck, even my UsbAmps uses exactly the same principle from 2013 onward as a button option. Unofficially, there were people seeing me use small screwdriver to connect D+/D- lines way before that. :)

This functionality is nothing special, nothing secret, nothing patentable, and definitely not magic. Paying for a $25 cable promising you magic when all it does is enabling something you can get either for free or for fraction of a cost is crazy in my opinion. To be completely fair, just based on images, it does look as a nice cable – those with fashion in mind might be able to justify $25 cable. Just don’t buy it for its technology.

And remember – with USB 3.1, its new connector, and a new USB Power Delivery standard all this will become pretty much irrelevant side note in the history of USB.

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