External power for Micro

Hi all!

For a school project I have to cheaply create a portable device that can run off its own power and be charged as necessary.

Currently I've been thinking of using an Arduino Micro due to its small form factor and because it outputs 5V.

Is there a way to power the Micro using a lithium ion battery pack that can be hidden inside a small enclosure and be recharged using a Micro-USB port?

If not, is there a similar board I can use that does something similar?

Thank you!

sq10:
and because it outputs 5V.

That is confusing.

Do you want to power something else that needs 5v power? If so, what is it?

Assuming you do NOT want to power something else ...

You can run a 5v Micro from a pack of 3xAA cells connected to the 5V pin. A single LiPo cell (nominally 3.7v) might work but obviously 2 LiPo cells (7.4v) would be too much for the 5v pin. The only possible problem using a single LiPo is that the Micro may be unreliable trying to run at 16MHz with a low voltage.

You can easily run a breadboard Atmega 328 at 8MHz from 2xAA cells or a single LiPo.

If you are using LiPo cells make sure that you have a safe charging system so that they don't burst into flames.

...R

Hi Robin,

I'd like to attach a water flow rate sensor to the Micro, which operates at 5V. However, I can't use AA batteries as it has to be rechargeable via a micro USB port.

Is there a particular piece of hardware I can purchase to attach a LiPo cell to the Micro and allow it to be recharged? I'm currently looking at something like this and wondering if it would work for the Micro, or if something similar was available: Adafruit LiIon/LiPoly Backpack Add-On for Pro Trinket/ItsyBitsy : ID 2124 : $4.95 : Adafruit Industries, Unique & fun DIY electronics and kits

Thanks!

sq10:
Is there a particular piece of hardware I can purchase to attach a LiPo cell to the Micro and allow it to be recharged? I'm currently looking at something like this and wondering if it would work for the Micro, or if something similar was available: Adafruit LiIon/LiPoly Backpack Add-On for Pro Trinket/ItsyBitsy : ID 2124 : $4.95 : Adafruit Industries, Unique & fun DIY electronics and kits

That board may well charge the Lithium battery, but what it does not appear to do is shut off the power when the battery discharges below the normal cutoff point of the battery, 3.0V.

Ever noticed that a mobile phone turns off when the battery is flat, this is for very good reasons, and one of the safety precautions neccessarily built into a phone.

If this is a school project I would stay well away from Lithium batteries, used incorrectly they are dangerous.

Even the 'experts' at Samsung got it wrong.

Unfortunately this school project requires it to be portable and small, without constant charging. Is there an external board or some code that can shut off the device when the LiPo becomes unsafe to use LiPo batteries safely with the Micro?

I'm sorry for sounding like a noob, but I really need this to work on a tight schedule and I would really appreciate any input everyone here may have!

Thank you!

Have you considered using 3xAA rechargeable NiMh cells?

as it has to be rechargeable via a micro USB port.

Is there a written specification for your project? If so please post it.

...R

Hi Robin, thank you for your answer!

Yes it would be greatly simplified if AA cells could be used but the product is essentially a smart water bottle where the water drank by the user needs to be measured, therefore the electronics enclosure should be as watertight as possible. Moreover, everything needs to be small enough so it fits into something like a water bottle cap or something at the bottom of the water bottle.

If LiPo batteries are really not worth the hassle, perhaps using smaller batteries would be better?

I look forward to any input :smiley:

When Lithium Ion or Polymer batteries are used in products the circuit will include some form of auto power off in the case of low battery.

This is not that difficult to arrange with a MOSFET or two, and a voltage supervisor device, or use the Arduino to measure the battery and turn itself off.

As an additional safety measure most Lithium Ion batteries include an internal cut-off, just in case the products normal power and charge control goes wrong.

And being in a rush is no reason at all to compromise on proper design and safety.

sq10:
Hi all!

For a school project I have to cheaply create a portable device that can run off its own power and be charged as necessary.

Currently I’ve been thinking of using an Arduino Micro due to its small form factor and because it outputs 5V.

Is there a way to power the Micro using a lithium ion battery pack that can be hidden inside a small enclosure and be recharged using a Micro-USB port?

If not, is there a similar board I can use that does something similar?

Thank you!

How small an enclosure - its simple to use a powerbank to provide USB power and they
are rechargable and easy to find.

sq10:
Yes it would be greatly simplified if AA cells could be used .... therefore the electronics enclosure should be as watertight as possible.

I don't understand the logical link. Why is it more difficult to make AA cells waterproof compared to LiPo cells?

I have the feeling that you know a lot more about this project that you have not yet told us.

If you really need a waterproof system you should put everything inside a sealed container and use inductive charging. Or maybe just have two protruding contacts like my shaver has.

...R

Adafruit powerboostc1000c or sparkfun battery babysitter. Ive used both, the latter has the higher power output but needs a boost reg if you require steady voltage.

Since you're already just buying a microcontroller, you just need to also buy a lipo charging circuit.
If you buy a microcontroller that runs at 3.3V, you can use a single 18650 cell.

Thank you for everyone's input!

I have decided I'll be using something like the PowerBoost 1000c, but since it is fairly expensive, I'll be using something like the Smart Electronics 5V Micro USB 1A 18650 Lithium Battery Charging Board and use another board to step up the output voltage from the board to 5V.

Will that work?

Thank you again for the help!