One of the duties that falls to us geek-of-the-family types is playing the role of the IT Help Desk for friends and relatives. In my case, I try to maintain my parents’ computer and connections even though they live 600 miles away. Without the ability to just show up when things go wrong, I need bullet-proof solutions.
Last summer I installed a combination cable modem and WiFi router, as it seemed like a simple solution for what they needed. But I didn't realize that their cable company has the ability to disable the WiFi radio in their modem using remote commands. Others experiencing this same problem with this particular company and modem were discussing it on a forum where I often lurk. Apparently it’s part of the cable company’s periodic maintenance routine to disable WiFi on company-owned routers where the customer hadn't paid for the WiFi option. The fact that the cable company didn't own this modem didn't matter - the commands kept coming, forcing my folks to have to connect via Ethernet cable and perform a complex set of operations in the Admin screens to reset the radio. The cable company zombies on the phone denied it (it’s not on their script) but after getting through to multiple technicians and spending a few hours at it, I determined that I would have to solve the problem without their help.
My solution was to buy a separate WiFi router (one they couldn't control) and connect it to one of the LAN ports. I found a tiny router - about 4cm square that required only a USB connection for power and the LAN cable; very simple and compact (and inexpensive). I configured the router at my house and ran it for a day or two, really trying to tax it by connecting five devices and streaming some video. It was rock-solid and I knew I'd be a hero...
Six hundred miles later, when I got to the folk's house and connected the new WiFi router, it became very unstable. One minute it was fine, the next moment it dropped the WiFi link. I could reconnect, but streaming video was impossible due to the interruptions. Can you guess the problem? I couldn't; at least not until hours later, when I realized there was one component in the system that had changed from my successful home tests...
The USB supply for the router was a cheap knock-off cell phone charger that I'd purchased for $2 on a site that shipped direct from China. Oops. After replacing it with a name-brand charger (with the exact same form factor), the router worked perfectly. I’m guessing that the cheap charger had either ineffective EMI filtering or poor output voltage regulation that caused the router to constantly reset. The charge was adequate for charging phones, but completely unusable as a 5V power supply.
USB began life as serial data port but morphed into one of the most ubiquitous battery charging power standards in the world. Youngsters might not know this, but there was a time when every cell phone came with its own proprietary wall charger. If you changed from, say, Nokia to Motorola, you'd have to replace all of your home and car chargers as well. Now, every phone I have can be charged from a USB port (although the phone end of the charging cable may still be proprietary for some phones).
Now we see USB further expanding its utility to go well beyond charging batteries. Many electronic devices now use USB for their primary power supply. However, my experience has shown that not all USB supplies are up to this new task. I've skimmed the USB 3.1 specification as well as the USB Battery Charging 1.2 specification and found no reference to any noise measurements. So I guess for now it's "buyer beware" and my advice is to stay away from the cheap knock-off devices if you need clean power to operate electronics devices...
Kelly Casey is VP of Engineering for FM Technical Consulting, and holds a Bachelor of Science Degree in Electrical Engineering from the University of Nebraska, as well as a Master of Science Degree in Electrical Engineering from the Georgia Institute of Technology. Previously, Mr. Casey has held various roles at Bourns, Littelfuse, and Teccor Electronics.