|
What time is it? (rant)
#290734 - 07/02/12 12:46 PM
|
|
|
I needed a clock for my apartment.
My requirements:
1) 24-hour format. (I truly do not grok how "3:00" can stand for a time in the afternoon, nor how "12:30" can stand for half an hour past midnight.)
2) Must be correctly readable from across the room, without my eyeglasses. (This is a real problem with 7-segment displays: the digits are usually smashed too close together, making it hard to tell which digit a given segment belongs to.)
3) Must indicate the date. (I don't have to read the date from across the room, just the time.)
4) Must keep good time. (It is lame to have to qualify "It's 11:28" with "by my clock".)
5) Must not be ridiculously expensive. (Nixie clocks, for example, are ridiculously expensive.)
You don't know how hard it is to find a clock that fits all these requirements unless you've looked. (It is hard.)
What I ended up doing was giving up and buying a kit, instead.
Alpha Clock Five (kit)
http://evilmadscience.com/productsmenu/tinykitlist/447-alphaclock
It was on sale for US$120 or so. And I had to buy solder and borrow a soldering iron just so I could get the bloody thing together and working.
For a number of reasons, including that the clock was not built to show the date, I knew I would need to modify the firmware. The firmware? Hoooo boy. Why don't you take a look?
http://evilmadscientist.s3.amazonaws.com/source/alphafive/alphaclock_18_Rev1_0.pde
It took me at least 16 hours of labor to get the thing working, correctly counting days as well as hours, minutes, and seconds, and correctly interfacing with the battery backup. And even now I'm not 100% sure I have it working properly.
Why, oh why, can't the %&$# free market even provide a decent clock for a decent price?
|
|
|
italie |
|
MAME owes italie many thank yous, hah
|
|
|
|
|
Reged: 09/20/03
|
|
Posts: 15246
|
|
Loc: BoomTown
|
|
|
|
Send PM
|
|
|
Just one question (yes, only one)
[Re: amused]
#290739 - 07/02/12 02:02 PM
|
|
|
> It was on sale for US$120 or so. And I had to buy solder and borrow a soldering iron
> just so I could get the bloody thing together and working.
You can afford $120 for a clock, but can't drop $9 on a soldering iron?
|
|
|
|
Re: Just one question (yes, only one)
[Re: italie]
#290745 - 07/02/12 02:40 PM
|
|
|
> > It was on sale for US$120 or so. And I had to buy solder and borrow a soldering
> iron
> > just so I could get the bloody thing together and working.
>
> You can afford $120 for a clock, but can't drop $9 on a soldering iron?
That I'm only going to use once?
|
|
|
| italie |
|
MAME owes italie many thank yous, hah
|
|
|
|
|
|
Reged: 09/20/03
|
|
Posts: 15246
|
|
Loc: BoomTown
|
|
|
|
Send PM
|
|
|
Re: Just one question (yes, only one)
[Re: amused]
#290747 - 07/02/12 03:47 PM
|
|
|
> > > It was on sale for US$120 or so. And I had to buy solder and borrow a soldering
> > iron
> > > just so I could get the bloody thing together and working.
> >
> > You can afford $120 for a clock, but can't drop $9 on a soldering iron?
>
> That I'm only going to use once?
Odd, for someone hanging around an emulation forum. I would have guessed that as a prerequisite or an "If I have the need I'm totally buying one" type of thing....
|
|
|
| Tomu Breidah |
|
No Problems, Only Solutions
|
|
|
|
|
Reged: 08/14/04
|
|
Posts: 6819
|
|
Loc: Neither here, nor there.
|
|
|
|
Send PM
|
|
|
Re: Just one question (yes, only one)
[Re: amused]
#290749 - 07/02/12 03:52 PM
|
|
|
> > > It was on sale for US$120 or so. And I had to buy solder and borrow a soldering
> > iron
> > > just so I could get the bloody thing together and working.
> >
> > You can afford $120 for a clock, but can't drop $9 on a soldering iron?
>
> That I'm only going to use once?
maybe this?
http://www.instructables.com/id/Guide-to-field-Soldering/
|
LEVEL-4
|
|
|
Re: Just one question (yes, only one)
[Re: italie]
#290750 - 07/02/12 04:02 PM
|
|
|
> > > > It was on sale for US$120 or so. And I had to buy solder and borrow a soldering
> > > iron
> > > > just so I could get the bloody thing together and working.
> > >
> > > You can afford $120 for a clock, but can't drop $9 on a soldering iron?
> >
> > That I'm only going to use once?
>
> Odd, for someone hanging around an emulation forum. I would have guessedthat as a
> prerequisite or an "If I have the need I'm totally buying one" type of thing....
The soldering iron was only a means to an end.
The end was getting a working clock in my apartment.
Now, my question is: why did I have to go to these lengths to get a working clock that doesn't suck? (See original post for definition of "does not suck" as it pertains to a clock.)
|
|
|
| Gor |
|
Giver of truth.
|
|
|
|
|
Reged: 09/21/03
|
|
Posts: 1925
|
|
Loc: The basement
|
|
|
|
Send PM
|
|
|
Re: What time is it? (rant)
[Re: amused]
#290754 - 07/02/12 04:21 PM
|
|
|
> I needed a clock for my apartment.
>
> My requirements:
> 1) 24-hour format. (I truly do not grok how "3:00" can stand for a time in the
> afternoon, nor how "12:30" can stand for half an hour past midnight.)
> 2) Must be correctly readable from across the room, without my eyeglasses. (This is a
> real problem with 7-segment displays: the digits are usually smashed too close
> together, making it hard to tell which digit a given segment belongs to.)
> 3) Must indicate the date. (I don't have to read the date from across the room, just
> the time.)
> 4) Must keep good time. (It is lame to have to qualify "It's 11:28" with "by my
> clock".)
> 5) Must not be ridiculously expensive. (Nixie clocks, for example, are ridiculously
> expensive.)
>
> You don't know how hard it is to find a clock that fits all these requirements unless
> you've looked. (It is hard.)
>
> What I ended up doing was giving up and buying a kit, instead.
>
> Alpha Clock Five (kit)
> http://evilmadscience.com/productsmenu/tinykitlist/447-alphaclock
>
> It was on sale for US$120 or so. And I had to buy solder and borrow a soldering iron
> just so I could get the bloody thing together and working.
>
> For a number of reasons, including that the clock was not built to show the date, I
> knew I would need to modify the firmware. The firmware? Hoooo boy. Why don't you take
> a look?
> http://evilmadscientist.s3.amazonaws.com/source/alphafive/alphaclock_18_Rev1_0.pde
>
> It took me at least 16 hours of labor to get the thing working, correctly counting
> days as well as hours, minutes, and seconds, and correctly interfacing with the
> battery backup. And even now I'm not 100% sure I have it working properly.
>
> Why, oh why, can't the %&$# free market even provide a decent clock for a decent
> price?
This does everything you require, needs no soldering iron, and tells you inside temperature as well.
Jumbo Giant Digital Atomic Wall Clock Thermometer.
It costs $93 shipped.
|
Oh for Pete's sake.
loser.com
|
|
| italie |
|
MAME owes italie many thank yous, hah
|
|
|
|
|
|
Reged: 09/20/03
|
|
Posts: 15246
|
|
Loc: BoomTown
|
|
|
|
Send PM
|
|
|
Re: Just one question (yes, only one)
[Re: amused]
#290755 - 07/02/12 04:22 PM
|
|
|
> > > > > It was on sale for US$120 or so. And I had to buy solder and borrow a
> soldering
> > > > iron
> > > > > just so I could get the bloody thing together and working.
> > > >
> > > > You can afford $120 for a clock, but can't drop $9 on a soldering iron?
> > >
> > > That I'm only going to use once?
> >
> > Odd, for someone hanging around an emulation forum. I would have guessedthat as a
> > prerequisite or an "If I have the need I'm totally buying one" type of thing....
>
> The soldering iron was only a means to an end.
>
> The end was getting a working clock in my apartment.
>
> Now, my question is: why did I have to go to these lengths to get a working clock
> that doesn't suck? (See original post for definition of "does not suck" as it
> pertains to a clock.)
The more you filter, the less results you return. It's kinda like getting laid. One could be bringing home action daily if one cuts their prerequisites to "breathing".
|
|
|
|
Re: What time is it? (rant)
[Re: Gor]
#290759 - 07/02/12 05:05 PM
|
|
|
> > Why, oh why, can't the %&$# free market even provide a decent clock for a decent
> > price?
>
> This does everything you require, needs no soldering iron, and tells you inside
> temperature as well.
> Jumbo Giant Digital Atomic Wall Clock Thermometer.
> It costs $93 shipped.
I wish I had known about this clock a few months ago.
I might still get one like it. Or maybe not.
There are two things I don't like about such clocks:
1) If it cannot receive the signal, the clock is useless.
2) The whole concept is a cop-out. The manufacturers are in effect saying that they can't be bothered to make accurate timekeepers.
|
|
|
|
Re: Just one question (yes, only one)
[Re: italie]
#290761 - 07/02/12 05:07 PM
|
|
|
> The more you filter, the less results you return. It's kinda like getting laid. One
> could be bringing home action daily if one cuts their prerequisites to "breathing".
Especially if "female" is not a prerequisite.
|
|
|
|
Re: What time is it? (rant)
[Re: amused]
#290763 - 07/02/12 05:25 PM
|
|
|
> > > Why, oh why, can't the %&$# free market even provide a decent clock for a decent
> > > price?
> >
> > This does everything you require, needs no soldering iron, and tells you inside
> > temperature as well.
> > Jumbo Giant Digital Atomic Wall Clock Thermometer.
> > It costs $93 shipped.
>
> I wish I had known about this clock a few months ago.
> I might still get one like it. Or maybe not.
> There are two things I don't like about such clocks:
> 1) If it cannot receive the signal, the clock is useless.
> 2) The whole concept is a cop-out. The manufacturers are in effect saying that they
> can't be bothered to make accurate timekeepers.
I bought that exact clock (from Amazon) in January, and am very happy with it.
The wall where I wanted to mount it had no reception for the clock signal, so I moved the clock around the house until I found the proper Colorado-facing window. Then, I removed the antenna/circuit board assembly from the clock and mounted it in that window, with a 4-conductor phone wire going back to the rest of the clock (through a hole in the wall behind it made several years ago for a different clock). -JW
|
|
|
| Stiletto |
|
They're always after me Lucky ROMS!
|
|
|
|
|
|
Reged: 03/07/04
|
|
Posts: 6472
|
|
|
|
|
|
Send PM
|
|
|
For reasons I can't explain, I love this thread. *nt*
[Re: amused]
#290769 - 07/02/12 05:51 PM
|
|
|
> I needed a clock for my apartment.
>
> My requirements:
> 1) 24-hour format. (I truly do not grok how "3:00" can stand for a time in the
> afternoon, nor how "12:30" can stand for half an hour past midnight.)
> 2) Must be correctly readable from across the room, without my eyeglasses. (This is a
> real problem with 7-segment displays: the digits are usually smashed too close
> together, making it hard to tell which digit a given segment belongs to.)
> 3) Must indicate the date. (I don't have to read the date from across the room, just
> the time.)
> 4) Must keep good time. (It is lame to have to qualify "It's 11:28" with "by my
> clock".)
> 5) Must not be ridiculously expensive. (Nixie clocks, for example, are ridiculously
> expensive.)
>
> You don't know how hard it is to find a clock that fits all these requirements unless
> you've looked. (It is hard.)
>
> What I ended up doing was giving up and buying a kit, instead.
>
> Alpha Clock Five (kit)
> http://evilmadscience.com/productsmenu/tinykitlist/447-alphaclock
>
> It was on sale for US$120 or so. And I had to buy solder and borrow a soldering iron
> just so I could get the bloody thing together and working.
>
> For a number of reasons, including that the clock was not built to show the date, I
> knew I would need to modify the firmware. The firmware? Hoooo boy. Why don't you take
> a look?
> http://evilmadscientist.s3.amazonaws.com/source/alphafive/alphaclock_18_Rev1_0.pde
>
> It took me at least 16 hours of labor to get the thing working, correctly counting
> days as well as hours, minutes, and seconds, and correctly interfacing with the
> battery backup. And even now I'm not 100% sure I have it working properly.
>
> Why, oh why, can't the %&$# free market even provide a decent clock for a decent
> price?
|
|
|
| Gor |
|
Giver of truth.
|
|
|
|
|
|
Reged: 09/21/03
|
|
Posts: 1925
|
|
Loc: The basement
|
|
|
|
Send PM
|
|
|
Re: What time is it? (rant)
[Re: amused]
#290773 - 07/02/12 06:45 PM
|
|
|
> > > Why, oh why, can't the %&$# free market even provide a decent clock for a decent
> > > price?
> >
> > This does everything you require, needs no soldering iron, and tells you inside
> > temperature as well.
> > Jumbo Giant Digital Atomic Wall Clock Thermometer.
> > It costs $93 shipped.
>
> I wish I had known about this clock a few months ago.
> I might still get one like it. Or maybe not.
> There are two things I don't like about such clocks:
> 1) If it cannot receive the signal, the clock is useless.
> 2) The whole concept is a cop-out. The manufacturers are in effect saying that they
> can't be bothered to make accurate timekeepers.
I'm betting the clock keeps accurate time even when it has no signal, the signal just allows it to
set itself to the atomic clock and positively ensure accurate time.
|
Oh for Pete's sake.
loser.com
|
|
|
Re: What time is it? (rant)
[Re: JWJr]
#290776 - 07/02/12 07:18 PM
|
|
|
> > > > Why, oh why, can't the %&$# free market even provide a decent clock for a
> decent
> > > > price?
> > >
> > > This does everything you require, needs no soldering iron, and tells you inside
> > > temperature as well.
> > > Jumbo Giant Digital Atomic Wall Clock Thermometer.
> > > It costs $93 shipped.
> >
> > I wish I had known about this clock a few months ago.
> > I might still get one like it. Or maybe not.
> > There are two things I don't like about such clocks:
> > 1) If it cannot receive the signal, the clock is useless.
> > 2) The whole concept is a cop-out. The manufacturers are in effect saying that they
> > can't be bothered to make accurate timekeepers.
>
> I bought that exact clock (from Amazon) in January, and am very happy with it.
>
> The wall where I wanted to mount it had no reception for the clock signal, so I moved
> the clock around the house until I found the proper Colorado-facing window. Then, I
> removed the antenna/circuit board assembly from the clock and mounted it in that
> window, with a 4-conductor phone wire going back to the rest of the clock (through a
> hole in the wall behind it made several years ago for a different clock). -JW
Oy.
What I don't understand is why they don't just measure the crystal frequency at the factory and program the ROM to compensate. (Clocks tend to be consistent in their errors.) Or provide a software equivalent of the "slow/fast" lever one sees on mechanical alarm clocks.
|
|
|
| italie |
|
MAME owes italie many thank yous, hah
|
|
|
|
|
|
Reged: 09/20/03
|
|
Posts: 15246
|
|
Loc: BoomTown
|
|
|
|
Send PM
|
|
|
Re: What time is it? (rant)
[Re: amused]
#290777 - 07/02/12 07:30 PM
|
|
|
> > > > > Why, oh why, can't the %&$# free market even provide a decent clock for a
> > decent
> > > > > price?
> > > >
> > > > This does everything you require, needs no soldering iron, and tells you inside
> > > > temperature as well.
> > > > Jumbo Giant Digital Atomic Wall Clock Thermometer.
> > > > It costs $93 shipped.
> > >
> > > I wish I had known about this clock a few months ago.
> > > I might still get one like it. Or maybe not.
> > > There are two things I don't like about such clocks:
> > > 1) If it cannot receive the signal, the clock is useless.
> > > 2) The whole concept is a cop-out. The manufacturers are in effect saying that
> they
> > > can't be bothered to make accurate timekeepers.
> >
> > I bought that exact clock (from Amazon) in January, and am very happy with it.
> >
> > The wall where I wanted to mount it had no reception for the clock signal, so I
> moved
> > the clock around the house until I found the proper Colorado-facing window. Then, I
> > removed the antenna/circuit board assembly from the clock and mounted it in that
> > window, with a 4-conductor phone wire going back to the rest of the clock (through
> a
> > hole in the wall behind it made several years ago for a different clock). -JW
>
> Oy.
>
> What I don't understand is why they don't just measure the crystal frequency at the
> factory and program the ROM to compensate. (Clocks tend to be consistent in their
> errors.) Or provide a software equivalent of the "slow/fast" lever one sees on
> mechanical alarm clocks.
If oscillator compensation was that easy, I'm sorry I left the field.
|
|
|
|
Re: What time is it? (rant)
[Re: italie]
#290778 - 07/02/12 07:36 PM
|
|
|
> > Oy.
> >
> > What I don't understand is why they don't just measure the crystal frequency at the
> > factory and program the ROM to compensate. (Clocks tend to be consistent in their
> > errors.) Or provide a software equivalent of the "slow/fast" lever one sees on
> > mechanical alarm clocks.
>
>
> If oscillator compensation was that easy, I'm sorry I left the field.
??!!!
For me, the clock was running a wee bit too fast, so...
I told it that there were 500012 microseconds in half a second! Problem solved!
|
|
|
| italie |
|
MAME owes italie many thank yous, hah
|
|
|
|
|
|
Reged: 09/20/03
|
|
Posts: 15246
|
|
Loc: BoomTown
|
|
|
|
Send PM
|
|
|
Re: What time is it? (rant)
[Re: amused]
#290779 - 07/02/12 07:48 PM
|
|
|
> > > Oy.
> > >
> > > What I don't understand is why they don't just measure the crystal frequency at
> the
> > > factory and program the ROM to compensate. (Clocks tend to be consistent in their
> > > errors.) Or provide a software equivalent of the "slow/fast" lever one sees on
> > > mechanical alarm clocks.
> >
> >
> > If oscillator compensation was that easy, I'm sorry I left the field.
>
> ??!!!
>
> For me, the clock was running a wee bit too fast, so...
> I told it that there were 500012 microseconds in half a second! Problem solved!
Problem solved at that specific temperature. Mess with your thermostat in the slightest and you might have just made things worse.
What you said isnt untrue, as long as ambeint is not a variable. I have some nice temp vs frequency charts I can post later, if you would like.
|
|
|
| italie |
|
MAME owes italie many thank yous, hah
|
|
|
|
|
|
Reged: 09/20/03
|
|
Posts: 15246
|
|
Loc: BoomTown
|
|
|
|
Send PM
|
|
|
Re: Just one question (yes, only one)
[Re: amused]
#290780 - 07/02/12 07:51 PM
|
|
|
> > The more you filter, the less results you return. It's kinda like getting laid. One
> > could be bringing home action daily if one cuts their prerequisites to "breathing".
>
>
> Especially if "female" is not a prerequisite.
Indeed.
|
|
|
|
Re: Just one question (yes, only one)
[Re: italie]
#290782 - 07/02/12 08:36 PM
|
|
|
> > > The more you filter, the less results you return. It's kinda like getting laid.
> One
> > > could be bringing home action daily if one cuts their prerequisites to
> "breathing".
> >
> > I assumed "breathing meant you'd already thrown out "female," as well as "old enough," "young enough," "human," and "mammalian."
|
|
|
| italie |
|
MAME owes italie many thank yous, hah
|
|
|
|
|
|
Reged: 09/20/03
|
|
Posts: 15246
|
|
Loc: BoomTown
|
|
|
|
Send PM
|
|
|
Re: Just one question (yes, only one)
[Re: TriggerFin]
#290784 - 07/02/12 09:07 PM
|
|
|
> > > > The more you filter, the less results you return. It's kinda like getting laid.
> > One
> > > > could be bringing home action daily if one cuts their prerequisites to
> > "breathing".
> > >
> > > I assumed "breathing meant you'd already thrown out "female," as well as "old
> enough," "young enough," "human," and "mammalian."
You have assumed wisely.
|
|
|
GatKong |
|
Tetris Mason
|
|
|
|
|
Reged: 04/20/07
|
|
Posts: 5907
|
|
Loc: Sector 9
|
|
|
|
Send PM
|
|
|
Did an elephant sit on your fence?
[Re: amused]
#290789 - 07/02/12 09:51 PM
|
|
|
Becuase then it would be time to get a new fence!
|
|
|
|
Re: What time is it? (rant)
[Re: italie]
#290792 - 07/02/12 10:01 PM
|
|
|
I have also had issues with clocks on some circuits depending on what else is on the circuit. Most extreme case my parents had a air filter which would freak out my clock (+/- 2 hours in 2-4 hours, why yes I like getting up a 5 am instead of 7 am). Got rid if the filter and that clock is usually +/- 1-2 mins per year. In the US its not that bad either as you set the clock about every 6 months anyway for DST. Though the red numbers are starting to fade due to age.
My fav is the one we have on the wall right now. The motor doesnt work very well. So therefor I leave an almost dead battery in it just so it moves once and awhile. The time is not very accurate due to a lack of power 
http://www.amazon.com/California-Clock-Co-Whatever/dp/B001G6MK64/ref=sr_1_2
|
|
|
|
Re: What time is it? (rant)
[Re: italie]
#290804 - 07/03/12 03:45 AM
|
|
|
> > For me, the clock was running a wee bit too fast, so...
> > I told it that there were 500012 microseconds in half a second! Problem solved!
>
>
> Problem solved at that specific temperature. Mess with your thermostat in the
> slightest and you might have just made things worse.
>
> What you said isnt untrue, as long as ambeint is not a variable. I have some nice
> temp vs frequency charts I can post later, if you would like.
I'd like to see them.
How bad is the problem, really? If it's not too bad, then (since the clock has a calendar) I could use a lookup table based on the month of the year. Assume 65 degrees F in February, 75 degrees F in August, that sort of thing, as the clock is for indoor use.
|
|
|
|
Re: What time is it? (rant)
[Re: lharms]
#290805 - 07/03/12 03:50 AM
|
|
|
> I have also had issues with clocks on some circuits depending on what else is on the
> circuit. Most extreme case my parents had a air filter which would freak out my clock
> (+/- 2 hours in 2-4 hours, why yes I like getting up a 5 am instead of 7 am). Got rid
> if the filter and that clock is usually +/- 1-2 mins per year. In the US its not that
> bad either as you set the clock about every 6 months anyway for DST. Though the red
> numbers are starting to fade due to age.
>
My guess is that your clock uses the mains frequency somehow.
I wonder why an air filter would mess up a clock like that.
My "alarm clock" is simply a battery-powered kitchen timer.
http://www.walmart.com/ip/Mainstays-Digital-Timer-with-Keypad-00535W/14913166
|
|
|
| italie |
|
MAME owes italie many thank yous, hah
|
|
|
|
|
|
Reged: 09/20/03
|
|
Posts: 15246
|
|
Loc: BoomTown
|
|
|
|
Send PM
|
|
|
|
> > > For me, the clock was running a wee bit too fast, so...
> > > I told it that there were 500012 microseconds in half a second! Problem solved!
> >
> >
> > Problem solved at that specific temperature. Mess with your thermostat in the
> > slightest and you might have just made things worse.
> >
> > What you said isnt untrue, as long as ambeint is not a variable. I have some nice
> > temp vs frequency charts I can post later, if you would like.
>
> I'd like to see them.
> How bad is the problem, really? If it's not too bad, then (since the clock has a
> calendar) I could use a lookup table based on the month of the year. Assume 65
> degrees F in February, 75 degrees F in August, that sort of thing, as the clock is
> for indoor use.
It isn't that simple, not even in a really good looking crystal as shown.
Below is a pretty decent looking and fairly well compensated AT cut crystal, @ 10MHz. The plot you see is the frequency deviation from nominal (10Mhz), shown in ppm (Parts per million). In this case that equates to about .07ppm total deviation(70 parts per billion) over the temp range of -45C to 80C (+/-32ppb would be the appropriate tagging). That would make for one rocking timepiece, but you'd be paying $30 - $70 for just the oscillator.
To put that in perspective, your average uncompensated quartz clock oscillator is listed around 10ppm. That'll get you to +/- one second a DAY.
The crystal below is compensated as an "oven oscillator". They actually put the crystal in a little sealed container, and using a PID or similar control circuit keep the "oven" at a specific single temperature just above the highest rated use temperature. By this method they remove temperature as variable and can, as you put it, "tell the clock to run a little faster" (or slower). Even with aging, drift, and jitter, you'd end up with a very accurate clock. That is the nature of an oven oscillator, your error follows a smooth and predictable curve. The drawbacks here are expense, power required to run the oven, and space. You'd end up with a clock control circuit that would chew through a few AA batteries in a week, cost $100 itself without any of the clock parts, and take up an inordinate amount of real estate. Not your hot seller, IMO. Now, on to part 2 and why this won't work in other situations...
[ATTACHED IMAGE - CLICK FOR FULL SIZE]
|
|
|
| italie |
|
MAME owes italie many thank yous, hah
|
|
|
|
|
|
Reged: 09/20/03
|
|
Posts: 15246
|
|
Loc: BoomTown
|
|
|
|
Send PM
|
|
|
|
> Now, on to part 2 and why this won't work in other situations...
(Forgive the borrowed data plot below, the results are consistent with expectations.)
Shown is a plot of a compensated TCXO. This is a more common and less expensive compensation method. You ~still~ won't find these in most clocks, at $2-10 a pop. This compensation method usually utilizes some form of reverse error generation applied to a crystals natural error curve. Generally you would run a crystal over temperature, capture it's frequency response, and then generate a 4th or 5th order polynomial equation for that response. To compensated for the error in any given crystal, you then would calculate a second polynomial equation to generate a cancellation signal to bring the crystal as near to nominal as possible. There are several means by witch to apply that correction to the crystal. All of them have their pluses and minuses.
When you are done, you have something that looks like the attached image below. Note that the response isn't as predictable and smooth as the last attachment. You might be thinking "I still don't understand why I can just store a table of values to compensate it further?" The answer to that lies in aging, drift, hysteresis, and the compensation method in itself.
Aging/drift - As the crystal is used and stressed, subtle changes will happen over time. You may still retain most of the compensatory effects, but all crystals do move. the amount of error at 25C today, may not be the amount of error at 25C next month. You'd have to re-train you values every so often, which isn't in the realm of possibility for most. You are being guaranteed +/- a certain spec over temp, not at defined error at a given temperature point.
Hysteresis - The crystal may not respond in the same manner when traveling forward on a temperature scale as it does in reverse. The amount of error you have compensated for in one direction, may be off a few degrees in the reverse direction. Due to the varied nature of the compensated curve this could be a minor issue, but could also produce very unexpected results.
Compensation - The nature of the beast itself is unpredictable. You are applying a polynomial response curve to a waveform taken once, twice if lucky. Your cancellation/correction curve will never change. Your crystal response will. This could lead to perturbations (random spikes), or even phase shifts. Depending on how the response curve is generated, there could also be hardware limitations to consider. Bottom line, even though you will stay within a certain range of accuracy, you won't always get the same response each time you sampled your compensated crystal over temp.
[ATTACHED IMAGE]
|
|
|
| italie |
|
MAME owes italie many thank yous, hah
|
|
|
|
|
|
Reged: 09/20/03
|
|
Posts: 15246
|
|
Loc: BoomTown
|
|
|
|
Send PM
|
|
|
|
And now, the $0.10 part they are putting in your clock. An uncompensated, 10ppm quantified piece of crap. You have little to no control over aging, phase shift, jitter, hysterisis, etc. They are guaranteeing your spec based upon averages in most cases. The error you are compensating for today might drift out by next week. You might get +.2 second accuracy today, and -1.2 tomorrow.
You might get lucky, and room temp might fall on a linear part of your response curve and leave you with a relatively predictable crystal. You might not get luck just as easily. There are no promises about anything, other than +- 10ppm.
Show, and not to scale, a plot of all three we've briefly touched on. In real-world plotting, the green "uncompensated" curve would be ~10x larger than the other two.
[ATTACHED IMAGE - CLICK FOR FULL SIZE]
|
|
|
|
Re: Xtal compensation theory 101: Part 2
[Re: italie]
#290822 - 07/03/12 11:04 AM
|
|
|
> Shown is a plot of a compensated TCXO. This is a more common and less expensive
> compensation method. You ~still~ won't find these in most clocks, at $2-10 a pop.
> This compensation method usually utilizes some form of reverse error generation
> applied to a crystals natural error curve. Generally you would run a crystal over
> temperature, capture it's frequency response, and then generate a 4th or 5th order
> polynomial equation for that response. To compensated for the error in any given
> crystal, you then would calculate a second polynomial equation to generate a
> cancellation signal to bring the crystal as near to nominal as possible. There are
> several means by witch to apply that correction to the crystal. All of them have
> their pluses and minuses.
"Reverse error generation"? "Cancellation signal"?
You mean, as opposed to a lookup table containing values such as "500000" and "500012"?
|
|
|
| italie |
|
MAME owes italie many thank yous, hah
|
|
|
|
|
|
Reged: 09/20/03
|
|
Posts: 15246
|
|
Loc: BoomTown
|
|
|
|
Send PM
|
|
|
Re: Xtal compensation theory 101: Part 2
[Re: amused]
#290824 - 07/03/12 01:42 PM
|
|
|
> > Shown is a plot of a compensated TCXO. This is a more common and less expensive
> > compensation method. You ~still~ won't find these in most clocks, at $2-10 a pop.
> > This compensation method usually utilizes some form of reverse error generation
> > applied to a crystals natural error curve. Generally you would run a crystal over
> > temperature, capture it's frequency response, and then generate a 4th or 5th order
> > polynomial equation for that response. To compensated for the error in any given
> > crystal, you then would calculate a second polynomial equation to generate a
> > cancellation signal to bring the crystal as near to nominal as possible. There are
> > several means by witch to apply that correction to the crystal. All of them have
> > their pluses and minuses.
>
> "Reverse error generation"? "Cancellation signal"?
> You mean, as opposed to a lookup table containing values such as "500000" and
> "500012"?
Yes. One solid difference is that most of these error corrections are generated real time (analog). A digital look-up table would require a huge resolution to be effective at anything other than one very precise fixed temperature (see oven oscilator, the only way this principle works to any degree of accuracy).
|
|
|
|
Re: Xtal compensation theory 101: Part 2
[Re: italie]
#290831 - 07/03/12 04:24 PM
|
|
|
> > "Reverse error generation"? "Cancellation signal"?
> > You mean, as opposed to a lookup table containing values such as "500000" and
> > "500012"?
>
> Yes. One solid difference is that most of these error corrections are generated real
> time (analog). A digital look-up table would require a huge resolution to be
> effective at anything other than one very precise fixed temperature (see oven
> oscilator, the only way this principle works to any degree of accuracy).
What do you mean by a "huge resolution"? Do you mean lost of entries? Or do you mean that the entries themselves would have a lot of digits?
What you could do is: instead of thinking in terms of cycles per second, think in terms of (pico- or femto-)seconds per cycle. The table would have entries like:
(figures pulled out of ass, for illustration only)
20.0 deg C: 0.000 000 999 999 95 sec
20.1 deg C: 0.000 001 000 000 00 sec
20.2 deg C: 0.000 001 000 000 07 sec
20.3 deg C: 0.000 001 000 000 18 sec
and you're smart enough to figure out what happens with each oscillation of the crystal.
|
|
|
|
Re: Xtal compensation theory 101: Part 2
[Re: amused]
#290832 - 07/03/12 04:27 PM
|
|
|
> What do you mean by a "huge resolution"? Do you mean lost of entries? Or do you mean
> that the entries themselves would have a lot of digits?
>
> What you could do is: instead of thinking in terms of cycles per second, think in
> terms of (pico- or femto-)seconds per cycle. The table would have entries like:
>
> (figures pulled out of ass, for illustration only)
> 20.0 deg C: 0.000 000 999 999 95 sec
> 20.1 deg C: 0.000 001 000 000 00 sec
> 20.2 deg C: 0.000 001 000 000 07 sec
> 20.3 deg C: 0.000 001 000 000 18 sec
>
> and you're smart enough to figure out what happens with each oscillation of the
> crystal.
Dude, stop fooling yourself. The only way to get serious accuracy is with a crystal oven.
|
|
|
| Gor |
|
Giver of truth.
|
|
|
|
|
|
Reged: 09/21/03
|
|
Posts: 1925
|
|
Loc: The basement
|
|
|
|
Send PM
|
|
|
Re: Xtal compensation theory 101: Part 2
[Re: Vas Crabb]
#290834 - 07/03/12 05:20 PM
|
|
|
> Dude, stop fooling yourself. The only way to get serious accuracy is with a crystal
> oven.
Oh boy, I'm really looking forward to the season premiere of Breaking Bad.
|
Oh for Pete's sake.
loser.com
|
|
| italie |
|
MAME owes italie many thank yous, hah
|
|
|
|
|
|
Reged: 09/20/03
|
|
Posts: 15246
|
|
Loc: BoomTown
|
|
|
|
Send PM
|
|
|
Re: Xtal compensation theory 101: Part 2
[Re: amused]
#290836 - 07/03/12 05:29 PM
|
|
|
> > > "Reverse error generation"? "Cancellation signal"?
> > > You mean, as opposed to a lookup table containing values such as "500000" and
> > > "500012"?
> >
> > Yes. One solid difference is that most of these error corrections are generated
> real
> > time (analog). A digital look-up table would require a huge resolution to be
> > effective at anything other than one very precise fixed temperature (see oven
> > oscilator, the only way this principle works to any degree of accuracy).
>
> What do you mean by a "huge resolution"? Do you mean lost of entries? Or do you mean
> that the entries themselves would have a lot of digits?
>
> What you could do is: instead of thinking in terms of cycles per second, think in
> terms of (pico- or femto-)seconds per cycle. The table would have entries like:
>
> (figures pulled out of ass, for illustration only)
> 20.0 deg C: 0.000 000 999 999 95 sec
> 20.1 deg C: 0.000 001 000 000 00 sec
> 20.2 deg C: 0.000 001 000 000 07 sec
> 20.3 deg C: 0.000 001 000 000 18 sec
>
> and you're smart enough to figure out what happens with each oscillation of the
> crystal.
So you have built your uber precise table based upon a very controlled data collection in a stable environment...
Then your dog sneezed on the clock...
Your table has just been invalidated, enjoy your recalibration.
Xtals are extremely sensitive to many factors, many of which I haven't even touched on. If you aren't compensating for them in some way, your tweaks are random and inconsequential minutes after they are implemented.
|
|
|
| Bekki Doll |
|
A cynical yet secular shiny retrogamer, thread ressurector and fan of the word "gay".
|
|
|
|
|
Reged: 01/28/12
|
|
Posts: 771
|
|
Loc: Freeport, PA
|
|
|
|
Send PM
|
|
|
Re: Xtal compensation theory 101: Part 2
[Re: italie]
#291086 - 07/07/12 12:05 AM
|
|
|
Quote:
Xtals are extremely sensitive to many factors, many of which I haven't even touched on. If you aren't compensating for them in some way, your tweaks are random and inconsequential minutes after they are implemented.
No wonder New Agers find crystals so mysterious. You can't control the crystal. The crystal controls you to the point of buying shiny sparklies at some roadside attraction somewhere in Arizona where the busses don't go. ;-)
--Bekki
|
Combating functional illiteracy with latex-clad drama since the '80s, because old video games rule!
|
|
Index 
Threaded 
What time is it? (rant)
Reply
[Re: 
