I have no idea what you are talking about. If you want to explain it, fine. But continuing to pull stuff from your back pocket is pointless.
I guess this all comes from having no indicated purpose to your exploration. So everything is an option. Whatever. When are you going to talk about moon rocks?
You quoted (above) my statement that in addition to 32768 Hz, there were 32767Hz (I typo'ed the number...) oscillators
available; I then suggested a use to which the latter might apply, and that it would have different energy cost seems likely. The mystery of a (2^15 - 1 ) Hz oscillator's purpose is open to other explanations: what's yours?
I have no idea what you are talking about. Sorry.
That applies only on low voltage (<1.5 V) wrist watch ripple counters, in which the output is effectively tri-state during each transition. Energy is consumed only charging and discharging the output stray capacitance. Even a very slow input transition doesn't cause extra dissipation.
In high voltage (>3 V) CMOS both the N and P FETs are conducting during the transition region, causing extra dissipation during each state change. This also defines the maximum allowed input transition times.
How would you implement the PRS shift register ? With some (mercury/glass) acoustic delay line ?
If with flip-flops, each flip-flop would operate a full clock frequency, consuming more power. For some number of stages a single XOR gate is sufficient, but some other lengths 2 or 3 XOR gates are required, each operating at full clock frequency.
Thus a ripple counter is preferable for low power dissipation
On a very high precision dividing engine, they started at the setting for 360 teeth on the circle, and then make the step length slightly larger (so the circle didn't quite close after walking around the circle, increasing the step size gradually until closure was again achieved. A version of Newton's method was used to improve convergence speed.
Joe Gwinn
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The point of a clocked timer is that it indicates when it has run a full many-clocks sequence. Both an array of flipflops, and a pseudorandom sequence generator, take many clocks to complete a sequence. Both are clocked, and can indicate a time at the end of the sequence. The fact that 'pseuorandom sequence generator' makes a sequence is interesting, but it is NOT the only function that that particular kind of hardware can serve. It also divides down a fast clock, if you note the occurrences of repetition of its state.
Sorry, you just are not explaining yourself. You don't need to explain counters to me. I just need to understand what you are doing. You seem to flail all around with no sense of purpose.
Oh, BTW, you seem to ignore the need for an N bit state detector for whatever is making your sequence generator. That's even more logic.
A multiplicity of powers of 2 are already present, in the (presumably) ripple-counter that divides down a 32.nnnn kHz rock to one minute, each stage being a divide-by-two flipflop.
The crystal frequency most convenient is what one would use, of course. It isn't arbitrary, it's specified.
Dividing a second clock by 60 does that, but there IS NO SECOND CLOCK. The powers-of-two clock division goes down to MINUTES to form a minute clock, and 1/64 minute is the closest item in the division chain to a second. We want uniform revolution of the second hand to complete one cycle in one minute; the seconds aren't electrical events, they're markings under the second hand on the watch face.
So? If you are designing a watch, and you find designing a divide by N counter to be remotely anything other than "convenient", you are in the wrong business.
You seem to be bantering wordplay now. I thought we were discussing engineering. Assume you have a boss, who asks, "Why are you using an oddball crystal frequency, when we already buy tons of 32,768 Hz crystals? Do you not know how to design a counter to produce a 1 minute clock from that frequency? If not, why would we let you design a chip for this watch?" How do you respond?
Only because you are using word play rather than designing anything.
Only if you are constrained on dividing by binary powers, which you are not.
Who cares??? You are saying the second hand does not use a second clock. That's irrelevant to the minute hand.
I have no idea what you are really thinking or what you are trying to do. Divide 32786 Hz by 32768 * 4 * 15 giving... wait for it... a minute clock. No rocket science involved and no need to specify unique, specific frequency crystals. Now, you only need to specify all the other details that impact the oscillator, start up, initial accuracy, drift, temperature compensation, etc. That's where you should focus your attention, to making the oscillator work as well as possible given the harsh environment it will be operating in. What's the point of an expensive, fancy watch that doesn't work any better than a cheap dollar store watch?
Of course, this is your idea, your product, except that it's not a product at all. It's play and you are free to do anything you wish with it.
It's my choice; I'm the customer.
You can choose to be constrained to one particular crystal. I do not so choose.
Huh? The minute hand wasn't going to need a divide-by-60, and the second hand doesn't need a divide-by-60, and the hour hand uses gears, not electronics. Why are you thinking there's a divide-by-60 issue? What got your head stuck in that particular box?
One makes seconds from a 32.768 kHz crystal, with a few flipflops. One makes minutes from a 30.720 kHz crystal, the same way.
Who's customer???
You seem to be deliberately thick about this. I've explained it clearly, even giving you the numbers. 32,768 Hz / (32,678 * 4 * 15) 4 * 15 is 60. It makes sense to split the 60 into a 4, which can be combined with the 32,768 leaving the 15. So, technically, you are right. There's no divide by 60.
No, I'm just being realistic about designing a watch. Also, dividing by 60 creates no issues. It's easy to do. It's often a small part of a junior level lab project.
Your minutes approach uses the identical number of FFs, not that it matters. You are designing a watch. What is the full feature set? Once you tell me that, I will give your more info about the divider chain.
No, I won't. You are not designing a watch. You are designing a divider chain for an imaginary timepiece with no other information. You are clearly being argumentative at this point. You have zero requirements. You've defined nothing about a product to be designed. You clearly don't understand digital electronics in detail, having made many mistakes. I can't see any reason to continue this discussion.
With 60 or 240 kHz crystal it is easier to implement 1/10 s (or 1/100 s) resolution stop watch functionality.
How do you implement such resolution with a 32768 Hz crystal ?
For equally spaced 1 second steps you divide by 546 52 times and 547 8 times.
For 0.1 sec you can't do it exactly, but dividing by 3,277 nine times and 3,275 once comes pretty close.
For 0.01 sec you divide by 328 68 times and 327 32 times which is again fairly close.
If you want to get cranky you can set up a phase locked loop to lock a 100Hz oscillator driving a 10:1 digital divider to the roughly 0.1Hz output - the low pass filter in the phase locked loop will take out most of the jitter , such as it is.
Do you really not know how?
NCO
Dither between two divisors and live with the jitter. No-one will *ever* notice unless they subject the thing to laboratory testing.
Since human reaction times are ~>100ms even for the best trained visual observers(*) the precision shown on such a toy chronometer is completely bogus anyway unless a robot hits the button.
(*) 150ms to 250ms is more typical for your average Joe.
0.1s is divide by 3277 4x and 3278 1x = 32768 0.01s is divide by 327 8x and 328 17x = 32768The 0.01s interval is still good to within 0.3% and 0.1s within 0.03% worst case. (it is actually better than that on average for 0.01s)
Watches are often designed with very low power consumption in order to maximize battery life time and hence avoid frequent battery changes. A battery change can be expensive and may risk the water resistance of the watch. A long life non-replaceable battery would be ideal, if it lasted 10 years or more.
With a 60 kHz crystal, one could use a 4 stage ripple counter to divide by 16 down to 3750 Hz followed by a 375 divider down to 10 Hz to drive the 1/10 s display.
The power consumption would be only twice compared to a ripple counter from 32768 down to 1 Hz due to the oscillator and first divider running about twice the frequency.
If it is acceptable to charge the watch as often as a mobile phone, why not. I have not checked for low power slow NCOs.
If power consumption is not an issue, I would make the NCO with a small 8 bitter uController, clocked at 32768 Hz and interrupted with a
16 divider chain (62500 us). If a 1 us resolution time accumulator is used, add 62500 to the time accumulator during each interrupt. There are more than 2000 clock cycles between interrupts, which is more than enough for doing four 8 bit additions with carry.With a processor, you could handle leap seconds standard/daylight time, time zone, weekday, date and leap year counting. These do not have to be done in the interrupt context, just calculate them in advance the previous minute and apply changes during the next full minute.
Counting the date of Eastern is a bit more complicated and depends of country :-).
And your proposal to use a crystal that divides by 2^N to make seconds instead of one that divides by 2^M to make minutes has absolutely no benefit.
I'm unaware of any reason a crystal manufacturer cannot make tuning forks for any note in the normal range of their product line, so I do not see an eonomic barrier. No one has offered a credible cost estimate.
No one has asked Statek to give bids for both proposed crystals, for comparison, so I question the assumption of cost.
I had a Casio watch that lasted twenty years (until it went through the washing machine) going through three lithium coin cells in the process.
If you could find a cheap close tolerance 60kHz crystal. The problem is that 32768Hz crystals are mass-produced in huge volumes and offer a much better cost-performance ratio.
So half the battery life.
If a mobile phone battery runs flat, the network resets it's clock when it gets recharged. That isn't an option with a watch.
It obviously is an issue.
<snip>
Yes it does!
32kHz watch crystals are about an order of magnitude cheaper than any custom low frequency crystal. There is one in every consumer item with a low power RTC as well as in watches - they are made in billions!They are about half the price of any other common LF crystals like 60kHz and 65.536kHz for example. Dividing by 60 is *NOT* that difficult!
It is up to you to find out how much they would charge you and what the minimum order is. ISTR when it was last done for sidereal rate it was ~$0.5 each minimum order 10k.
Today you can get a 32k watch xtal for ~$0.2 (and less in bulk)
The advent of cheap PICs like the 16877 pretty much did for that ancient swap the crystal way of making a sidereal clock. That had enough legs to direct drive an LCD display and very low power operating modes.
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