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1  Using Arduino / Storage / Re: Circuit which powers Arduino long enough to save program state to memory on: April 26, 2011, 08:02:09 pm
@RuggedCircuits 's post Act on loss of 5vdc partially answers my question. Thanks!
Help for my remaining questions is still very welcome and appeciated!

Answered so far:
3a) A "super" capacitor can hold the power. Ratio in example circuit: Needs 4 minutes to fully charge, supplies emergency power for 3 seconds. That's a proper ratio for my application!
3b) Through a diode voltage drop/loss can be measured on a Arduino analog pin.
4) The Arduino has an internal EEEPROM of 512 bytes, which is totally satisfying for my application!

What remains open:
Ad 3a) The provided example uses a 0.47F capacitor. In what price range is that? A quick search showed me products for about 50 EUR. I hope I was searching in the wrong sections! I imagined rather a price range of 0 - 3 EUR. Possible? What exact type of capacitor do I need?
Ad 3b) The provided code shows that the voltage monitoring must run continously in the main loop. Is there no interrupt/event implementation within Arduino. (Sorry if my question is naive, I am a newbie)

2  Using Arduino / Storage / Circuit which powers Arduino long enough to save program state to memory on: April 26, 2011, 07:27:48 pm
I am asking for circuit design & programming implementation ideas for my Arduino application, where I want to save a certain program state (in my application, only a simple counting number) to non-volatile memory (NVM), so that my application can continue from its saved state after an intended shutdown or unintended power loss.

Both these events are expected very rarely, the intended shutdown in the range of days, the power loss optimistically never, but realistically, lets say in the range of days to weeks.

Basically 3 methods came to my mind, sorted from least to most efficient:

1) Regularly write that data to NVM. Con: Saving the state, so that it make sense, must happen in the range of seconds, whereas powerdown is in the range of days. This ratio is very inefficient, as it wears down the NVM unnecessarily and wastes tons of processing cycles.

2) Write that data to NVM on user event (key press), who does this prior intended shutdown. Con: Still cannot handle the case of an unexpected power loss!

3) Build the circuit in a manner, where in case of circuit power loss:
a) A certain circuit component continues to power the Arduino for a short "emergency shutdown" period,
b) A certain circuit component triggers the Arduino,
c) This event triggers the routine "save program state to non-volatile memory".

Is this possible? Suggestions for circuit & code implementations please!

Detailed considerations:
3c) About how long is this emergency shutdown period? The current stuff must run, then the emergency save state function, maybe still something else I don't consider now, etc. About how much altogether?
3a) Hence what characteristics must the component have to properly power the Arduino through that emergency period?
3b) Is their an intended standard procedure? Does the Arduino have something like interupt/event handling? Or must it be implemented entirely individually through circuit & code?

And 4) What's the best (= Cheap, simple, but still reliable and satisfying for my described purpose) NVM for my application, if I only need to save a few bytes, at most lets say 1k?
3  Community / Website and Forum / Re: Please offer board model comparison chart / table on website! on: April 21, 2011, 04:35:40 am
@Msquare: Meanwhile, even before I read your reply  smiley , I did this! At I completed some informations, and normalized the table's data/layout and made the table a subchapter, so that it can be properly referenced.
But nevertheless, I am a newbie and outsider, and as such, I lack a) the necessary overview & b) the ability to state correct / precise factual information, as my knowledge is only secondary!

@Editor: Therefore, the most reliable comparison chart / table would come from the official team / editor!
Team, please consider this inquiry! Thanks!
4  Community / Website and Forum / Please offer board model comparison chart / table on website! on: April 20, 2011, 03:56:30 pm
Dear website editor! Dear Arduino team!

I was new to Arduino, and I wanted to get an overview over the available models in order to buy the right model(s) for my project. Thus I went to:

This page describes the overall characteristics of each device, which gives a first rough idea. All details can then be viewed on every model's own page.

But what was missing for me, was a comparison table!!! To have a handy tool for quickly comparing the hard facts, in order to decide which (combination of) model(s) meets the expectations of your project (best).

I did a web search for terms such as "Arduino board model comparison table chart etc", but the results were either:

It would be very cool if your page would feature such a comparison table, preferable with sort and filter options!

Regards, Stefan Nowak, Vienna
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