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Connecticut
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I thinking of making a project using a RTC (which draws 1.5mA), an ATtiny85 (200mA max), and an LED (30mA). I want to power all of these @5V with a battery, smallest possible. I've seen many batteries at sparkfun which have the capacity, and using a booster, the voltage.


But, I am thinking of having the whole project in a enclosure, with only holes for switches and power plugs. Can I, and how would I, setup a circuit that would use a wall wart to charge the battery, without removing it from the circuit? (A DC jack on the side of the enclosure would be nice) (Just like consumer electronics. You can run your laptop off the battery for x hours, then you can plug it in. At this point it charges AND runs off the wall wart. I want something like this.)

Which battery would be the best?


Thanks!
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Denver
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Do you need to run at 5V?
If you want to charge in circuit a lipo might be the easiest route. Something like this could be an option:
http://www.sparkfun.com/products/10161

Note that the ATtiny will actually use less current at a lower voltage, and fortunately, it won't be near 200Ma no matter how you run it.

Also if you want to DIY and don't mind soldering an SOT you can get a sample of a MAX1555. It will charge a 1 cell lipo from either USB or wall wart.
« Last Edit: February 11, 2011, 05:22:08 pm by BroHogan » Logged

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Connecticut
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I need it @5V. For what I'm doing, 4.5-5.5V power supply is needed to operate.

On the one you showed me, do I need to use USB? Or can I solder headers into the two pins below the Charging LED?
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Connecticut
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And which battery do you recommend? (It will need to power all the components I mentioned previously.)
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Denver
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Well, if you really need to run at 5V and and want to recharge in circuit you can use something like this:
http://www.sparkfun.com/products/10300

(You really need to check it out for yourself - I'm just putting out ideas.)

That board has pins for 5V input and a USB conn. But even if it had only a USB conn. you can use a wall wart that looks like this:
http://www.sparkfun.com/products/10214

Your choice of battery depends -
- Your going to go with LiPo?
- How long must it run before it is put on charge?
- How much current does your circuit really draw?
- Size issues? Cost issues?

Once you know the current and time between charges you can cal how many mAH your battery should be.

With the little bit of info I have here I'm really shooting in the dark here, so this is the best I can do.




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I'll wait until I get all the other components and report back.

Bye for now.

baum
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Denver
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Glad I can help.
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