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Topic: Running Arduino-compatible from batter(y|ies) without regulator (Read 2 times) previous topic - next topic

cefn

I'm wondering what's the simplest and possibly cheapest portable power arrangement to keep an ATMega328P-PU or ATMega328-PU alive.

There are plenty of approaches involving a power regulator (and a power source > 5v) or a boost regulator (and a power source < 5v). However, I'm wondering if it's possible to simply power a 328 directly off some kind of battery technology which produces a voltage within the right sort of range, to maximise simplicity and minimise cost of tutorials and demonstrations.

So far I've been speculating about...

  • 3 AA NIMh batteries, coming in at about 3.6V 4.2V when fully charged

  • 1 Lipo battery, about 3.7V when fully charged


...but there may be other arrangements I should consider or concerns I should have.

I can't find a pre-existing discussion about this as I think most projects assume they are using a full-fledged Arduino including a regulator, or that 5V is important for some reason. Anyone have experience of running off batteries without any regulator?

In our case we're relying on Arduino-compatibility, but we're building simple ATMEGA328-based projects direct on stripboard, like this...
http://cefn.com/shrimping/Shrimpduino_bb.png
...so the minimum component count and most consistency between running off USB and running portable the better. I don't think the exact voltage matters for us, so long as the microcontroller is running stable.

When any battery technology starts to go flat, I guess we'll need a 328P with picopower to handle a graceful brownout, though. Don't know what the consequences would be of using the simpler 328 without picopower on a battery-driven project. Perhaps it could corrupt the bootloader when it starts to run random instructions?

Update: I finally found this thread http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1295580639 but seems to be inconclusive, with Jeenode offered as an example of running at 16MHz with low voltage and some saying chips will happily run down to 2.5 volts, whilst others saying it won't work.

PaulS

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or that 5V is important for some reason.

You are trying to imply that it isn't?

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I don't think the exact voltage matters for us, so long as the microcontroller is running stable.

There is a big difference between exact voltage and consistent voltage. Batteries will give you neither.


BulletMagnet83

Given their low cost I'd really REALLY consider using an LDO regulator when running from batteries. I wouldn't feel comfortable feeding any microcontroller-based project from an unregulated supply, even from batteries. It doesn't really add much complexity to the circuit :)

cefn


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or that 5V is important for some reason.

You are trying to imply that it isn't?


Given Jeenodes are running at 3.3v and regular Arduinos at 5V I had the impression that the voltage could be anywhere in the range from 3.3v to 5v and from the thread I linked to, perhaps even a wider range than this. Perhaps you're alluding to something bad which happens when the supply voltage changes while a sketch is running. Perhaps you're trying to underline my ignorance. I'm a bit confused by your question.


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I don't think the exact voltage matters for us, so long as the microcontroller is running stable.

There is a big difference between exact voltage and consistent voltage. Batteries will give you neither.


It may not be clear from my wording, but these are unknowns for me - my main reason to raise it on the forum. If you know a reason why regulating the power supply to 5V IS important, please share. Equally if you have notions of 'exact' and 'consistent' for voltage which corresponds with the well-functioning of ATMEGA328 projects when powered by batteries, then I'm all ears. The insights promised by your post could mean I have no choice but to include a regulator. However, I don't think I can guess what those insights are, yet.

cefn


Given their low cost I'd really REALLY consider using an LDO regulator when running from batteries. I wouldn't feel comfortable feeding any microcontroller-based project from an unregulated supply, even from batteries. It doesn't really add much complexity to the circuit :)


One of the aspects of the way we're workshopping with the ATMEGA chips is to try and maintain continuity as much as possible from one stage to the next. Ideally the exact same solderless breadboard circuit powered off the CP2102 attached to a laptop is transferred to stripboard wholesale, without having to rethink or rewire it. One way to go is to include the LDO regulator in the circuit even when it's not strictly needed (e.g. when attached to the regulated USB supply). That way we can switch seamlessly from the USB-connected lab-prototyping mode into a battery-operated in-the-field mode without any sleight of hand.

Do you think this would work? I gather there's a loss of voltage when going through a regulator, but given the spec of the component you described this may not be significant.

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