Entries from March 2012

Embedding Videos Elastically

I've meant to make and share more videos for some time now, ever since my first smartphone brought with it a decent video camera, in fact. This has meant diving deeply into technical subjects I had previously neglected, wrestling with various open-source video editors, and, of course, updating my blog theme so that I could properly embed YouTube iframes into posts. This last turned out to be surprisingly difficult.

B-29 Superfortress “Fifi”

I had the pleasure this weekend of seeing the only presently flying example of the B-29 Superfortess, a salvaged plane named “Fifi” that was restored and is kept airworthy by the fine people of the Commerative Air Force. A recently restored P-51D Mustang, “The Brat III” was also on display, and the public could even fly in both planes. I couldn't afford that ($570 to $1395 for the B-29, depending on the seat, $1995 for the P-51) but was very happy taking a tour through the bomb-bay and cockpit.

By the way, I only became aware of Fifi's visit to Fort Lauderdale Executive Airport because I happened to be overflown at low altitude by it, heard a somewhat remarkable noise, and was surprised to find a B-29 overhead. A little google-searching revealed what was going on this week. Either the CAF might want to try to get the word out more effectively, or I need to be more plugged into the local aviation and warbird community, if such exists. Any suggestions to that end will be appreciated.

Postel's Prescription and Power Polarity

Be liberal in what you accept, and conservative in what you send.

Postel's Prescription, by Jon Postel

I have a day job as a hardware engineer for a telecommunications company, and in this capacity I'm often designing equipment to be installed in phone company Central Offices (COs). Unlike the designers of consumer electronics or data center hardware, I can rely on having DC available to power my devices; COs have “rectifier plants” that convert mains AC to 48-volt DC and distribute this power through the facility with giant copper or aluminum busbars over the racks.

Most CO equipment uses two-pin Phoenix-style connectors as power inlets. These come with a pluggable terminal block with screw-down style connectors that accept bare wire from the rack's fuse and power distribution panel. Because installers wire this plug on site and mistakes are easy to make, it's good sense (and company policy) for the hardware designer to put a bridge rectifier across the input leads so that this connection can be insensitive to polarity.

This is an application of the first part of Postel's Prescription, “be liberal in what you accept”, to power engineering. If the second part, “conservative in what you send”, has an analogue in this field, it could be this: make sure your power outputs, if any, have clearly defined polarity. Another possible analogue would be: keep the output to a tighter voltage range than the telecom standard 36-72 volts.