[time-nuts] Mechanicrawl (San Francisco, July 12th)
hmurray at megapathdsl.net
Mon Jul 14 16:09:37 EDT 2008
I was in San Francisco on Sat for the Mechanicrawl.
For time-nuts, the Long Now was probably the most interesting place. They
are building a mechanical clock that is targeted to run for 10,000 years.
They had lots of neat prototype stuff working. I didn't get the big picture.
It's half art and half engineering.
I think the plan is to power the core timekeeping unit from day-night
temperature differences and let visitors/tourists provide power for the fancy
They have a big Fresnel lens that's somehow rigged up with a PLL. They are
keeping solar time, not atomic time.
Pampanito is a WW II sub.
They had a TDC (Torpedo Data Computer) on display. It was in the shop where
you could see it. (There was another in the sub, but the sub itself was
The TDC was close to working. It's a mechanical analog computer. Inputs are
your speed and direction and (estimates) of the target's bearing, speed, and
direction. It sets the bearing on the torpedo's gyrocompass. Being able to
track that in real time was a major advance.
The guy said they were expecting 40-50 geeks. Word got out. They had 1000
or 2000 visitors.
I didn't see it on the tour, but the Pampanito has Loran gear.
The DAS-3 LORAN is in the control room. It was used to
locate the boats position when close to shore based
transmitter stations. A replacement is installed in control
room. It powers up, but otherwise the status is unknown
since the LORAN signals it uses are no longer transmitted.
We would like to simulate these signals with a computer for
testing, or find one of the WW II era testing devices.
Each pulse is 40 microseconds. At 1.75 to 1.95 MHz, that's about a dozen
cycles. My straw man would be a 1 bit D/A from a FPGA and a low pass filter.
Maybe 2 bits on a center tapped transformer for better symmetry.
Next to the Pampanito is the Jeremia O'Brien, a WW II Liberty ship.
The steam engine was running. If size is your criteria, it was clearly the
hit of the crawl.
I didn't see anything timing related, but they did have a neat counter down
in the engine room. It counted rotations. It had a lot of digits.
Next time, I'll have to remember to find the clock. There are a lot of
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