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cheap Chinese electronics
Friday, January 5 2007
I've done a lot of work with electronic devices in my life. Some of that work has involved experiments with opening cases, soldering wires to various pins, and supplying power from alternate sources. In the course of such experiments there are plenty of ways to screw things up. But it's been rare for me to actually destroy electronics, even when doing things like accidentally supplying voltage backwards, handling CMOS circuitry without concern for electrostatic discharge, or wantonly shorting out pins. Most electronics, I've inferred, is protected by safeguards against a ordinary electrical insult. Today, though, I noticed that I'd managed to destroy a USB hub and the device-end electronics of my 100 foot USB cable down in the boiler room. They were probably destroyed a couple weeks ago when I accidentally shorted a 38 volt relay-driving power line to ground. Such a short shouldn't have caused any damage except to the 38 volt supply (which, because the short was only momentary, was fine). But for some reason it killed those two USB devices. The short must have been powerful enough to raise the ground line's voltage in relation to the USB devices' five volt line, causing a lethal backwards-wired voltage. It existed for only a moment, but it was a moment too long. Both USB devices were cheap Chinese imports, the kind that come in boxes written in butchered English. My guess is that the manufacturerers of such devices have found numerous ways to shave tiny amounts off the price of assembling these items, probably by skipping the use of zener diodes, power supply chips, and other protective measures. The lesson for me is that I must disconnect the USB cables from devices when doing risky mid-voltage work.
Today was another warm sunny day, the kind that wouldn't be out of place in May. But of course it wasn't May, it was January 5th in the dead of winter. I was in Woodstock today and it was perfectly fine weather for walking the length of downtown in a teeshirt to grab a slice of pizza. Wintertime inertia prevailed at the pizza place and tables hadn't been set up for those wishing to eat outdoors.
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