AA Batteries and 7 Segment ?

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#1
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Guys,

How long will it last for 4 AA batteries with Atmega128 driving 6 digits seven segments ?

Thanks

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depends on the quality of the batteries and the amount of current you will be drawing from them.

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how much power will brand new 1 AA battery have ?
2.5Ah ? I measured just now, the circuit's consuming 0.29A....

The battery will last for 2.5/0.29 = 8.62 hours ...
?

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that again depends on the type of battery used...
recharchable, alkaline, lithium,
and also what vendor is used, that also can make big difference.
look for duracell, energizer, varta, sony, panasonic, GP(goldpeak) and have a look at the datasheets they have on their batteries.

note that most of the times you will only get to about 80% of the rated power before the cell voltage drops to much. but that again depends on the amount of current drawn vs the rated current of the battery used.

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Did you sleep through all your schooldays?

A typical AA cell is 2100mAh. e.g. 2.1Ah / 0.29A = 7.24 hours.

If you have 4 cells in parallel. i.e. 1.5V @ 0.29A
this means 0.0725A per AA cell.
So 2.1 / 0.0725 = 28.9 hours.

I suspect that you have your AA cells in series. i.e. 6V @ 0.29A. Hence 7.24 hours.

Google is your friend: [url]http://www.allaboutbatteries.com/Energy-tables.html[/url]

Note that a single D cell is far better than multiple AA cells in parallel. And if you use a voltage-boost chip, you can create the exact running voltage for your project.
Using 6V to power LEDs with a forward voltage of 2.5V is wasting most of the energy.

David.

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Probably this one ?
[url]http://ww2.duracell.com/media/en-US/pdf/gtcl/Product_Data_Sheet/NA_DATAS...

Yes I need 6V but can last for few months if possible...

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It would be wise to start with making a power budget then.....
what currents are consumed at what voltages.
what power does your total solution draw in that case.
followed by the choice of batteries.....
and the amount of them.

do not forget to also see if you can get them in enough quantity. We made that mistake once and that was not fun so to say.

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One month = 31 days @ 24 hours = 744 hours.

Your PDF shows a 2100mAh cell.

So from my previous calculation, you will need to replace the cells ten times every month.

If you want 100Ah batteries, use a car battery.

OTOH, you put your brain into gear.
Who or what is going to see your display?

If it is a human, you could ask her to push a button to wake up your product. It then runs the LED display for 10 seconds and goes back to sleep.

On this basis, your AA cells may run for a year.

The wake-up source could be a proximity detector. It will take some current but could mean that the punter never sees a blank display. e.g. ask your mother whether the fridge light stays on when she shuts the door.

Ok, the battery may have to supply power for the whole time that the punter is in the room (or has the fridge door open). But this is likely to be less than 24 hours a day.

David.

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I want to make it on the whole day....I think power supply from main is the solution...currently I use 6V 300mA adaptor...

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That is absolutely fine.

You do the calculation for battery life.
Discover it won't last for 24 hours.

Choose mains power.

If you have measured the average current as 290mA, bear in mind that the peak current will be considerably more.

Measure the current when you display "8.8.8.8.8.8."

Select your mains adapter to give you a safety margin.

If you want the display to run 24 hours, you might consider altering the brightness when a human is active.

David.

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Quote:

If you want the display to run 24 hours, you might consider altering the brightness when a human is active.

As David says, you don't need the LEDs to be on all the time. Most multi-digit 7seg use some kind of multiplexing so you don't have all the digits on all the time anyway.

EDIT: actually we now know from your other thread (I love cross posts) that your design is based on this:

http://www.avr-tutorials.com/pro...

Those SeData/SegCtl writes at the heart of the main while(1) are doing the multiplexing in fact.

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You're right Clawson,
so far it's displaying clock correctly already..
Have a watch:
[url]https://www.youtube.com/watch?v=T4lXFbzntFw[/url]

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Use an LCD instead of LEDs for low power?

Imagecraft compiler user

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Is there any 7 segment LCD with the size of 4" ? thanks

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Have you Googled?

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I hate it when the specs dribble out one at a time over dozens of messages. Can you just give us an overview of the gizmo and what it does? "Its a battery powered 6 digit 7 segment clock with 4" tall digits and has to run for a month". If we tell you you need a school bus battery is that ok? You cant post requirements that are unachievable, so just put em out there and lets look at em.

Imagecraft compiler user