Computing stuff tied to the physical world

Long live the AA battery!

In Hardware on Sep 17, 2010 at 00:01

The AA Power board announced yesterday just arrived:

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And it looks like it does indeed perform exactly as expected. Here’s the ripple:

Screen Shot 2010 09 16 at 13.41.07

That’s with the 1.6 mA LED load, i.e. a 75 µs cycle / roughly 13 KHz – this was as predicted: at light loads, the recharge frequency can reach down into the audible range. But it’s highly unlikely to be noticable due to the tiny size of the inductor, which after all is not built to act as a loudspeaker :)

Here’s the “AAv1″ fully mounted for powering a JeeNode via the FTDI connector:

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(there’s no charge circuit here, I’m just using an externaly-recharged battery as power source)

And here’s the whole setup in actual use:

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Works like a charm. Runs just fine with the “rooms” and “radioBlip” sketches, and wireless just works – as before.

Quiescent current draw is about 20 µA when powered this way. That goes down to 10 µA when used with two cells @ 2.4V, and down to an amazing 7 µA when powered from a 3V source (a CR2032 ought to work nicely!). Above 3.3V, the circuit becomes just a tad less efficient when it switches into step-down mode, drawing about 30 µA all the way up to 5.5V.

Great, now we’re starting to get into some serious low-power options.

Tomorrow, I’ll describe other ways to use this new AA Power board…

  1. This is great! When can we buy these from the shop?

  2. Me first me first! :-D

  3. That battery looks pretty Apple-ish :)

  4. This is very interesting!

    Have you thought of connecting two AA in parallel? There is a double (and quadruple) battery holder of the same type you use for that purpose. It is used in some toys to give them a better endurance.

    • What advantage do you see in connecting two AA in parallel over putting them in series? If my calculation is right, the quiescent power draw is 24µW in both cases.

      When using three or more cells the numbers suggest that a parallel setup would draw less power in quiescent mode, but those savings might easily be eaten up by cross currents between the cells if they are not exactly balanced regarding capacity and charge condition.

  5. Very interesting – might be interested in hooking this up to 4 x AAs instead of using them directly. Any idea how much longer this might be expected to last?

  6. @aamv & @tanskslappa – now :)

    @bmj – as Reinhard points out, two AA’s in series will be more efficient (and you can drain the batteries to an even lower level). Also: 2xAA is wider than a JN.

    @ed – by the same reasoning, 2x AA on parallel, i.e. 2.4V or 3V will last longer – at 4.8V (6V is too high), the regulator goes into a less efficient step-down mode (still much better than a linear VR, I expect).

  7. @jcw and @Reinhard The battery holder stacks the battery ON TOP of each other and is not wider then the JeeNode and that is way I pointed it out. It is a direct replacement of the one on in your picture. Because the holder is made of ONLY metal it MUST connect the battery’s in parallel (god or not). I know of the cross current problem and that way a asked if you have tested this. My guess (from RC-car radios) is that 2 dry-cells (single use) would last 1.8 times as long as a single cell. Rechargeables charge by a single channel/cell charger 1.7. But a RC-car radio uses much more current. I buy one board and test it (-;

  8. @jc Sound of rapid typing, creaking of wallet opening, tap tap tappity tap…

    new email bong Thank you for placing your order with The Jee Labs Shop!

  9. JC, can you tell me how that inductor looks like ? I am looking for an underwater sound source (up to 200khz) without the resonance found in piezo stuff. this might be usable if indeed it produces audible sound.

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