powering my project

Hi First time posting here. I have just finished my first arduino project prototype and it is all running nicely on breadboard. It's currently powered through usb but will be required to work outdoors from battery in practice.

I would like to make the finished device rechargeable and as efficient as possible so I plan on using switching regulators and lithium batteries. I have both 5v and 3.3v components to power as well as the 5v arduino micro.

I need to be able to use the usb port on the arduino micro to connect to a PC GUI I have written in order to download data collected on the arduino.

So my idea was to use a 7.4v lithium rechargeable battery to power a 5v switching regulator and connect this to the 5v pin on the arduino....thereby bypassing any inefficient linear regulator. For my 3.3v components I am undecided on whether to use a second 3.3v switching regulator or to use the 3.3v pin on the arduino and accept some inefficiency.

I would also like to be able to easily charge the battery bearing in mind everything will be contained in a waterproof enclosure. The ideal scenario would be to charge the battery through the arduino usb socket but I realise this could be difficult to achieve...perhaps a more realistic goal is to have a separate charging socket on the side of the box.

My background is software and none power electronics...which is why I have come for advice and help with the power side of things which I'm less familier with.

I would be greatful for any advice or potential pitfalls or suggestions you may have on this topic. Any advice on circuit design welcomed and recomendations of components to use especially for the battery and regulators as I haven't sourced these before.

In terms of power requirements...I haven't measured the current draw accurately yet but the whole thing is running perfectly well if usb current

Thanks in advance

If you are willing to work at it, you can get an Arduino to run for a couple of years on 2-3 AA cells.

See Nick Gammon's excellent tutorial on power savings.

See also the solar powered Arduino project.

If you switch to a 3.3v Micro you could run everything from a couple of AA cells without any of the losses associated with a voltage regulator.

Another option might be to use an Atmega 328 on the breadboard rather than the Micro. It needs very few external components if you use the 8MHz internal oscillator and will easily run from a couple of AA cells or a 1s LiPo. You can upload programs with a USB-TTL cable. With NiMh cells or a 1s LiPo you could use a very simple charging system. Personally I would choose the Nimh cells for safety.

...R

Where do you get a 3.3v micro? All the ones I can find seem to be 5v. I have seen a few on eBay but they seem to have less pins than the one I'm using? I need all the pins for my project.

thorntonforce: Where do you get a 3.3v micro?

When I bought my 5v pro-micro I thought the supplier also had 3.3v versions but now I just see 3.3v version of the pro-mini.

AFAIK Sparkfun makes a 3.3v pro-micro.

...R

Where do you get a 3.3v micro?

ATmega processors run on any voltage between about 2 and 5V.

On any Arduino you can remove the voltage regulator and associated parts by just swiping them off with a hot solder pencil tip.

The caveat for 3V operation is that you must lower the clock speed to 8 MHz, which is easily done by changing the fuses to use the internal oscillator instead of the crystal/resonator.

Gotta watch the generalities.

Some "ATmega processors run on any voltage between about 2 and 5V. "

Some, like the Atmega2560 on the Mega, need 4.5V to 5.5V only.

Atmege2560V can run on 3.3V.

jremington: On any Arduino you can remove the voltage regulator and associated parts by just swiping them off with a hot solder pencil tip.

Seems much simpler (and cheaper) just to use an Atmega 328 on a breadboard or a piece of veroboard. :)

...R