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Saturday, January 8, 2005

Entropic Storm: Zap a Laptop

It's hardly a news flash that it gets cold in Switzerland in the winter, especially at Fourmilab's altitude of 806 metres above mean sea level. When it's cold outside, relative humidity inside plunges, and static electricity manifests itself everywhere in irritating fat blue sparks whenever finger approaches metal. Humidifiers mitigate the effect, but you can't use them everywhere, and they don't help when you've been outside and just walked into a warm room, fully charged.

For the most part, this is a minor annoyance, but after I migrated my development work to a Dell Inspiron 9100 laptop a few months ago, it's been a matter of some concern because on three separate occasions so far I've entered the computer room from outside, touched the metal frame of the work table on which the computer sits (as I always to do discharge any static electricity before touching the computer keyboard or mouse), and had the laptop immediately power down without any soft shutdown of the operating system whatsoever.

Apparently this computer is unusually vulnerable to EMP discharges in its vicinity, so much so that simply discharging static electricity to the metal frame which supports the particle board table on which it sits is enough to make it turn itself off.

The Dell mains adaptor has a three prong grounded plug, and I verified with an ohmmeter that when it's plugged in, the chassis of the laptop is grounded to mains safety ground. Since the metal frame of the table wasn't grounded but was simply serving as a charge sink, perhaps it was acting as an antenna to deliver the electromagnetic punch to the guts of the Dell.

In any case, these static zap induced power downs are extremely irritating and risky to work in progress, so to attempt to avoid them I cobbled up this grounding strap to create a low impedance ground between the frame of the work table (which I always touch before touching the computer keyboard or mouse) and the chassis of the computer, via the safety ground of the UPS into which the laptop's power brick is plugged.

The ground wire is a sturdy solid copper conductor, soldered to the lug, which is fastened with a self-tapping 3.5 mm screw and lockwasher to a hole I bored in the table. The other end of the ground strap is connected to the safety ground terminal of the mains plug, the other two pins of which are unconnected. Steel is sturdy stuff! It took the better part of an hour, off and on, to bore a 3 mm hole through the frame of the table, which is only about 1 mm thick. A drill press would have made quick work of the job, but I don't have one and wouldn't want to tear down the table anyway, so I used a handheld drill instead. Yes, I powered down the computer so its hard drive wouldn't be spinning while I bored the hole in the table.

Does it work? Well, I don't know yet. I'm not about to deliberately charge myself up and try an experimental zap. I'm sure the inevitable inadvertent shocking event will put the gizmo to the test in the near future, and I'll let you know whether it worked when that happens.

Posted at 17:13 Permalink

Comet Machholz Passes the Pleiades

machholz_pleiades_2005-01-07.jpg

The weather was murky with occasional drizzle most of today, so I wasn't optimistic about spotting the passage of Comet Machholz (C/2004 Q2) past the Pleiades tonight, but a couple of hours after sunset the falling temperature forced the ground fog to a lower altitude and the sky was exquisitely transparent. The comet was an easy object for the unaided eye, about two degrees to the southwest of the Pleiades, and with 15 power 50 mm binoculars the inner coma and nucleus were visible and the overall green colour of the coma obvious. (The colour is due to cyanogen (CN) and diatomic carbon (C2) in the coma, both of which fluoresce in the green when illuminated by sunlight.)

After the rather disappointing results of my first attempt to photograph this comet on the morning of the fifth, I decided that with a comet this dim and no clock drive, aperture was king, so I mounted a thirty-year-old Nikkor 50 mm f/1.4 lens on the Nikon D70 digital SLR and made time exposures at f/1.4 with CCD sensitivity set to the equivalent of ISO 1600. The off-axis performance of this vintage lens at full aperture is execrable, so I was careful to centre the Pleiades and comet in the frame. The image above is cropped from the original and reduced by 50%, which almost conceals the small star trails visible in the full scale image.

Both the dust and ion tails of this comet are extremely subtle and I have neither spotted them visually nor picked up the slightest hint of them in a photograph.

Posted at 00:18 Permalink