It’s that time again. Soon I will head out “on the road”. This time (yet another) trip to Spain. In transit, I will be away from home, and face the constant challenge of keeping electronic devices including my mobile phone and tablet charged. Often that means plugging a charging device into an electrical outlet (“mains” to you Brits). But sometimes, the convenient place to charge is at a public charging station that provides a “USB” socket for a charging cable.
OK, although I think of myself as “prudent”, others characterize me as a raving paranoid! Let’s just say that safety is a good policy. There have been reports of public charging stations that take advantage of travelers plugging in cell phones etc,. will use that opportunity to either steal data from the device, delete files, or plant malicious files on the phone. After all, that USB cable you use to charge your phone is the same cable you can use to transfer data back and forth between your mobile phone and your computer.
When we read stories like that, there is always a bit of doubt as to whether the reports of data theft are real, or just an excuse to sell a solution to the “problem”.
I have a fair amount of experience with USB charging/data cables from my work on the ESL-Kiosk project. I knew that USB cables involve four wires: two that transmit power and two that transmit data. I had experienced difficulties as I did intensive market research to find suitable cost-effective (cheap!) MP3 players for the classroom. Sometimes cheap USB cables used only two rather than four wires. This made them usable for charging but not file transfers.
Armed with that knowledge, I thought that somebody must make a simple USB dongle that blocks transmission of the data signals from one end to the other. Easy-peasy! (and obviously very cheap to make).
Well, indeed such devices are available. On Amazon, they sell for $7 – $20!! Hardly cheap!!
OK, full disclosure, Amazon is usually NOT the cheapest source for consumer goods. I did check eBay and Aliexpress, where I found devices for as little as $3. But, procrastination leaves me without the option of waiting a couple weeks to a month to receive something from Aliexpress!
As I pondered my (paranoid) dilemma, I glanced over at my bookcase and noticed a couple of (cheap!) short USB extension cables. I have no memory of what possessed me to ever buy uselessly short “extension” cables. But, there was my answer!
I grabbed a couple nearby tools… (Don’t try this at home folks!)
Making a careful, sort incision (slicing open!) in the middle of the cable, I examined the wires. Black, white, yellow and red. Well, it was reasonable to guess that the black and red wires carried power. So I boldly clipped the white and yellow ones.
I tested connecting my phone to my computer. Using a regular USB cable, a message appeared on the screen to allow the option of just charging, or performing data transfer. I then plugged my homemade safety-cable into the charger and my normal cable from it to my phone. It charged, and did NOT offer to transfer data!
OK, one small detail about the USB standard is that normally it will not “charge” at more than one half amp. By “shorting” each exposed white-yellow pair, more current is allowed to pass.
All done, a bit of black electrical tape to cover the wound in the cable, and I am ready to rock and roll!!
Afterword: The less paranoid out there will point out that my phone did provide protection. It *asked my approval* before changing from charging to data-transfer mode. Most devices do that. So in the end, I suppose I spent a bunch of time in a useless exercise in paranoia. Well, I enjoyed it! 😉