how accurate is the clock? particularly on the a570is and a590is - Script Writing - CHDK Forum
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how accurate is the clock? particularly on the a570is and a590is

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Offline mattkime

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how accurate is the clock? particularly on the a570is and a590is
« on: 21 / November / 2008, 01:29:17 »
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I want to take a pic every five minutes. preferably at 00, 05, 10, 15 etc on the hour.

i need to make sure that the camera doesn't suffer from clock drift if i want to base script execution on it.

does anyone have experience with this? i guess i'll keep an eye on the camera clock for a couple of days but it would be nice to compare to other people's experiences.

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Offline fudgey

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Re: how accurate is the clock? particularly on the a570is and a590is
« Reply #1 on: 21 / November / 2008, 16:31:45 »
I think I set the date & time on my a570is about a year ago and looks like it's drifted less than a minute.
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Offline mattkime

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Re: how accurate is the clock? particularly on the a570is and a590is
« Reply #2 on: 22 / November / 2008, 16:18:44 »
thats great news.

now, one more question.

how long does the clock/setting battery last? is it affected by whether the camera has continuous power?

if i want to leave the camera set up for extended periods i need to figure out a schedule of replacing the battery.

i think the battery lasts a few years but i'm curious if i should replace the battery every year
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Offline fudgey

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Re: how accurate is the clock? particularly on the a570is and a590is
« Reply #3 on: 23 / November / 2008, 05:05:30 »
I don't know. Usually people have charged batteries in their cameras at all times so without measuring those currents it's hard to tell where the RTC current is taken from. But typically a battery like that is able to run a clock for years.

Remember that the a570is (and likely a590is) is not able to startup automatically from USB power or external power unless you wire or mechanically press the power buttoin?
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Offline Hacki

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Re: how accurate is the clock? particularly on the a570is and a590is
« Reply #4 on: 23 / November / 2008, 05:13:56 »
My SX100 drains 0.00 ampere when its on my power supply, without batteries. I guess the RTC takes its power from the button battery alone.

I remember the battery of my A410 was perfectly fine for 4 years. (Camera dead by now, battery still fine, runs my grandmas wristwatch now  ;) )

Also, i remember the clock always being extremely accurate with little to no drift..

Out of curiosity: Why do you need such extreme accuracy? Would it be really that bad if a picture is 1 sec off?



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Offline fudgey

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Re: how accurate is the clock? particularly on the a570is and a590is
« Reply #5 on: 23 / November / 2008, 05:46:32 »
You need a few more zeroes in your current reading to find out how much it drains... typical RTC chips draw less than 0,000001 A.

And many gadgets have very inaccurate clocks. Heck, my Philips wake up light (which in essence is an alarm clock) drifts about 10 minutes a year (sad especially since it could sync its clock from mains frequency). I'd take it back for warranty but that's just one of its several usability disasters.
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Offline Hacki

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Re: how accurate is the clock? particularly on the a570is and a590is
« Reply #6 on: 23 / November / 2008, 05:52:40 »
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You need a few more zeroes in your current reading to find out how much it drains... typical RTC chips draw less than 0,000001 A.

Thought so. But my cam's clock resets when its button battery is taken out, even when it has its NiMH batterys or is connected to the psu, so i assume the clock & the rest of the camera have seperated power circuits.

Quote
And many gadgets have very inaccurate clocks.

Agreed.. even my PC would be lost without NTP.  :D

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Offline fudgey

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Re: how accurate is the clock? particularly on the a570is and a590is
« Reply #7 on: 23 / November / 2008, 07:09:41 »
Quote from: Hacki on 23 / November / 2008, 05:52:40
Thought so. But my cam's clock resets when its button battery is taken out, even when it has its NiMH batterys or is connected to the psu, so i assume the clock & the rest of the camera have seperated power circuits.

Ah, it's probably the same for all cameras and good news for mattkime. I can't do that test on my camera because the coin cell is only accessible after opening the 2*AA battery cover, which disconnects the batteries. External PSU is another thing, though, I know the camera doesn't use the AA batteries at all when it's connected (the camera shuts down with full batteries is external PSU voltage dips too low).
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Offline fe50

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Re: how accurate is the clock? particularly on the a570is and a590is
« Reply #8 on: 23 / November / 2008, 07:42:48 »
...Just for information...

The Ixus cameras don't have such an exchangeable battery (coin cell).
They have an extra, built-in & soldered-in Li-Ion accumulator as backup battery which is loaded by the main battery or the external power supply.
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Offline mattkime

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Re: how accurate is the clock? particularly on the a570is and a590is
« Reply #9 on: 23 / November / 2008, 17:53:25 »
great info!

its not that the pics can't drift a second or two - its my worry that the drift would be accumulative. i want to set the camera up to run for a year so there's plenty of time for that to happen.

its interesting that the Ixus cameras don't have the coin cell. any idea why that is? would it affect the reliability of the camera's clock?

it sounds like the Ixus would run longer with less maintenance  but i'd need to be assured that i'm not compromising time accuracy. then again, i'm not sure i'd want to hunt down an Ixus model for such a small concern.

anyway, i'm definitely going to run a loop checking the time before hitting the shoot() function. too bad Lua doesn't appear to support camera events.
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