[time-nuts] Mechanicrawl (San Francisco, July 12th)

Hal Murray 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 
display stuff.

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 
really tight.)

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.

http://www.maritime.org/radiocat.htm says:
    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 
distractions though.

These are my opinions, not necessarily my employer's.  I hate spam.

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