PENDULUM DRIVE

I am working on a board with a STM32F2, it has RTC "calibration" registers that allow you to add/subtract cycles every minute or so.

Not got into it much yet, but I notice that the 16MHz crystal seems much more accurate and stable than the 32kHz one. And you can use the 16MHz to calibrate the 32kHz!

I have used a solution like that on a PIC to digitally trim a nominal

A roughly one ppm tweak on a 8192Hz master clock rate being a cycle added or subtracted every 2 minutes. It was and is surprisingly accurate and I never bothered to do any temperature compensation.

Trouble is faster clock speeds do take more power (although these days they have become astonishingly frugal).

nt in a school house wall clock with a $12 single AA battery operated quar tz movement which has a swinging pendulum for appearance only, The clock ru ns at the correct rate whether the pendulum is there or not.

ed movement which was temperature sensitive. I had to keep adjusting its pe ndulum length as the average room temperature changed summer-winter.

ensitive or even inaccurate? If it doesn't synchronize to NIST, it's junk.

temperature and can be trimmed with the load capacitor. They drift by aroun d 5-10ppm for a +/- 10C change in ambient temperature.

ut pretty badly. Older Meade LX200 scope have that problem and they "fixed" it by adding GPS capability rather than a trimmer capacitor!

the daylight saving hour on and off automatically.

registers that allow you to add/subtract cycles every minute or so.

more accurate and stable than the 32kHz one. And you can use the 16MHz to c alibrate the 32kHz!

IIRR the sweet spot for oscillator crystals was at 10MHz. The charm of the

Awesome! I imagine it's 'gut wrenching', putting electronics onto a rocket.

George H.

On Tue, 12 Nov 2013 06:26:59 -0800 (PST), George Herold Gave us:

The solder joints were all kept as small as possible.

And they could have been exotic solders too.

Not like this Tin based CRAP the euro Al Gore idiots saddled the world with.

nsitive or even inaccurate? If it doesn't synchronize to NIST, it's junk.

You're being drawn into the ideal conditions trap. That crummy 32kHz crysta l clock will get bad real fast as the battery runs down or it gets temperat ure cycled by a few degrees here or there. It might take a few weeks but it will happen. There is nothing more aggravating than seeing multiple clock displays with different readings, and in this day and age that is a very li kely scenario with all the portable devices and their NTP clocks or whateve r(s). The NIST synchronized clocks are inexpensive and will flip seconds re adout in synchronization, they are impervious to operating conditions effec ts. NIST clocks ( aka "atomic clocks" to the consumer ) determine time zone as well as daylight savings, and can be programmed to display the time in any of the 360/15= 24 time zones around the Earth.

I can tell you from personal experience that I get 10 years from a Duracell AA in the pulsed solenoid ratchet type clock mechanisms and that HAS to dr aw more current than the simulated pendulum. So you should plan on the batt ery lasting for its shelf life, meaning a D-cell will probably last no long er than the AA.

The GPS clocks were not really 'gut wrenching'.

My adventures on Johnston Island in 1962 were, especially when they had to disintegrate a nuclear weapon on a failed Thor launch and spread plutonium all over the place:

And, to learn more about JI:

Jeff

The worst clock we own is the one in a small GE microwave oven at our office. The damn thing gains well over a minute a day and there's nothing reasonable I can do about it. (Except junk it, but it heats stuff just fine.)

I don't know what the timing source is, but its clearly not a decent xtal or synced to the 60 Hz line powering the oven.

I'm guessing they left the line syncing out so they could use the same electronics with just a power transformer change when they sell the same oven in countries with 240V/50Hz line voltage.

Jeff

The reason for using a magnet core in a kicker solenoid is for situations where it kicks BOTH ways. Kicking in both directions is not a necessity so the magnet could be a plain iron slug, right? Some kickers use the current induced by the magnet to feed timing circuitry but generally a plain iron slug still retains enough magnetism to be detected as well, doesn't it? A magnet core is not absolutely required is it? Further, is feedback from the slug in coil even necessary for a pendulum kicker to work? If the kick is timed to the right frequency doesn't the pendulum sync to it? As in the old synchromotors which had no magnets?

On Tuesday, November 12, 2013 10:37:56 AM UTC-5, snipped-for-privacy@gmail.com w rote:

tal clock will get bad real fast as the battery runs down or it gets temper ature cycled by a few degrees here or there. It might take a few weeks but it will happen. There is nothing more aggravating than seeing multiple cloc k displays with different readings, and in this day and age that is a very likely scenario with all the portable devices and their NTP clocks or whate ver(s). The NIST synchronized clocks are inexpensive and will flip seconds readout in synchronization, they are impervious to operating conditions eff ects. NIST clocks ( aka "atomic clocks" to the consumer ) determine time zo ne as well as daylight savings, and can be programmed to display the time i n any of the 360/15= 24 time zones around the Earth.

But who really cares? My wristwatch is accurate within about 30 siconds pe r month. And I can not think of anything that I need the time more accurat ely than that.

Dan

YECCH!

Mine loses

Wait until the battery starts to get low and just watch that thing gain 30 seconds per hour.

LOL- what year is that approximately?

It's not like the "atomic" clocks are expensive. Here's about the most inexpensive one available from a /reputable/ manufacturer-also displays calender info and temperature too:

Like the 70s-80s was the era of putting a digital clock in everything, and now it's the era of temperature and possibly humidity.

That's essentially what our TOD clocks do. A thermistor is used to determine how often cycles are dropped. If there is a GPS in the unit, it will be used to update the whole thing.

The nice thing about the 32kHz watch crystals is that the curve is inverted 'U' shaped with the zero d%F/dT spot at about 25C.

We bought it about 3 to 4 years ago.

Jeff

-- Jeffry Wisnia (W1BSV + Brass Rat '57 EE) The speed of light is 1.8*10^12 furlongs per fortnight.

That's a good signal that the battery should be replaced.

Jeff

I don't own a watch but the big deal is not 30 seconds, rather having to reset it at all.

Sounds good, but in actual fact it keeps good time right up to when it stops because the battery is too low.

Dan