Help Me Learn About Batteries in Relation to Arduino

Forgive me in advance, this may be a pretty stupid couple questions. I am new to Arduino and everything about wiring, and I recently had an idea for a very simple project… The thing is, I’m not sure if I can power it the way I want to.

The build is a necklace. In my head, I wanted the necklace to contain an Arduino Mini board (or the smallest board available) and a single LED, and the LED would simply cycle in brightness to “pulse” between a minimum and maximum brightness level.

However, it is a necklace (therefore small). For this build to work the way I want it to without trailing an obvious wire in to an external battery pack, I would have to use very small batteries (I was thinking cell/watch/hearing aid batteries). In the research I have done, it seems that I could not use such small batteries for any meaningful length of time, even for powering just the one LED and the board.

So I have two questions:

  1. Am I correct in assuming that I could not power the Arduino Mini and one LED with one or two cell batteries? If so, what sort of battery would be the minimum I would need to power these for around 3 hours?

  2. Any suggestions where I could learn more about batteries, power requirements, and Arduino board-specific power requirements? Honestly I’ve been reading through some of these forum posts about power draw and batteries, and I’m still not sure how to figure out the specs of boards and specific batteries and what they mean.

You should have a look at Nick Gammon's power saving tutorial

...R

Thanks for that resource! I did some looking around in there, and I don't know what a lot of it means yet, but I think I am a bit closer to the answer.

According to that tutorial, a CR2032 battery (the cell battery with the highest amount of mA hours) has a capacity of 210 mA hours. Also according to the tutorial, a regular Arduino Uno draws about 50 mA (with a sketch that only has the setup and loop functions in it), and according to a quick google search, an LED at maximum brightness takes about 20 mA...

New additional questions:

  1. According to the specs of the Arduino Mini, the board's operating voltage is 5V, but a CR2032 battery is only rated at 3V. Is it possible to lower the board's normal operating voltage so it could be powered by a single CR2032 battery? If not, would using two CR2032 batteries increase the total voltage to 6V so the board could be powered at its normal operating voltage?

  2. In theory, if I used one CR2032 battery and the board+LED power draw summed up to 70mA (ignoring self-discharge rates for now), that would mean I could run that board+LED for 3 hours, correct? And if I could use two of those batteries, it would last for 6 hours?

I know you can buy a 3.3v version of a Micro so maybe you can also get a 3.3v version of a Mini. The only difference is that, at the lower voltage it can only operate at 8MHz.

Your calculations in Part 2 are correct. But, for long battery life you would put the Arduino to sleep for a large proportion of the time. And you would not be using a battery like that if you want ax brightness from an LED.

...R

Yes, 3.3V/8MHZ Promini is available. I'd suggest removing the Power LED, powering it from VCC (vs RAW) to bypass the voltage regulator, do Nick's power saving tips, lower or turn off the brown out detection fuse, use the clock divider to run at a lowew frequency, and then use a really high brightness LED (5,000 mCD or more) that will be plenty bright at low mA levels. Of course, the battery is still only spec'ed for low current levels: Typical Drain @ 2.9V: 0.19 mA And this article http://www.embedded.com/electronics-blogs/break-points/4429960/How-much-energy-can-you-really-get-from-a-coin-cell- So running it at 10x that, 2mA, may drop the voltage faster than the 200+mAH ratings might suggest.

2 AAAs or 2 AAs in a cylindrical holder would likely perform better and longer.

Thank you for the suggestions... I'll look in to doing all the power saving tips once I confirm that this project will actually work and buy the board.

Do high-brightness LEDs come in RGB or just Green? The LED I need for this project has to be green (this is a costume prop).

I understand that using AAA or AA batteries would possibly work better to power something like this effectively, but I would still like to use cell batteries if I can manage a battery life of 3 hours or more. Because this is a costume prop, I want to eliminate the need for an external battery pack if I can.

Let's assume I can definitely put two CR2032 batteries in to this in series, I use a high brightness LED, and I use an Arduino Pro Mini-- would that work to make this project do what I want it to do? If not, would applying all the power-saving tips make it work?

The trouble with these coin cells is that the internal resistance is so high, a lot of them aren't even capable of driving such high currents, regardless of capacity.

A long time ago I tried using a CR2032 for a backup to put a microcontroller board to sleep if power was lost. During testing, it only powered the board and flashed a small 0603 LED for about 30 seconds before dying.

If it's only a pulse though, maybe adding a cap in parallel with the output will reduce the equivalent output impedance.

Stry: According to that tutorial, a CR2032 battery (the cell battery with the highest amount of mA hours) has a capacity of 210 mA hours. Also according to the tutorial, a regular Arduino Uno draws about 50 mA (with a sketch that only has the setup and loop functions in it), and according to a quick google search, an LED at maximum brightness takes about 20 mA...

Can you say what you want to achieve ? If it is just some flashing lights perhaps a hardware solution will be appropriate. An arduino mini is bigger than a couple of pen cells anyway how do you intend to hide it.?

Boardburner2: Can you say what you want to achieve ? If it is just some flashing lights perhaps a hardware solution will be appropriate. An arduino mini is bigger than a couple of pen cells anyway how do you intend to hide it.?

According to the product page, the normal Mini is 30mmx18mm... which is small enough for my purposes, and I can hide it and fit in two cell batteries. That's not the problem.

The sum total of what I wanted to do with this is: 1. Make one 5mm green LED gradually grow dimmer and brighter, cycling continuously. 2. Power the board and the LED without having to use an external battery pack. 3. Have the battery last for at least 3 hours.

If that is just not possible for cell batteries then I'm just going to scrap the project. I just wanted to know if this was even feasible.

How much time do you have to experiment with it? If it was me, I'd throw something together on a breadboard and just test it. The ATmega328 should work fine at 3V so you could experiment with different configurations like two batteries in parallel and/or using an output capacitor etc.

I think the previous posts are right: you're up against battery life big time, plus the size of the board, unless you are prepared to design your own and use a surface-mount Atmega chip (if such a thing exists).

How about buying a ready-made toy and re-purposing it? I've got a 4-LED "light sabre" which uses three LR1130 cells and one of those tiny PCBs with a custom IC on it underneath a black epoxy blob. you're welcome to it if you want; just send me a PM.

Pat-The-Pirate: and use a surface-mount Atmega chip (if such a thing exists).

Of course they exist - they are probably more common than the DIP version.

But I don't see any particular value in using a surface mount version rather than the DIP version. It is easy to build the DIP version into a stripboard circuit.

...R

You could also try the ATTINY85, which is even smaller and for your needs would be more than adequate to the task, costs under $1.50 on ebay, comes in versions that include a USB stick-like connector, and I'm guessing uses even less current than the smallest 328-based board and could potentially be powered by a 2032 (that's almost exactly the same size) for hours, perhaps longer.

Here's one that I recently bought but haven't yet gotten around to using:

http://www.ebay.com/itm/142062832671

You could even conceivably use the built-in user-controllable LED (while disabling the power LED) to accomplish your goal, by simulating PWM through software.

habanero:
You could also try the ATTINY85, which is even smaller and for your needs would be more than adequate to the task, costs under $1.50 on ebay, comes in versions that include a USB stick-like connector, and I’m guessing uses even less current than the smallest 328-based board and could potentially be powered by a 2032 (that’s almost exactly the same size) for hours, perhaps longer.

Here’s one that I recently bought but haven’t yet gotten around to using:

http://www.ebay.com/itm/142062832671

You could even conceivably use the built-in user-controllable LED (while disabling the power LED) to accomplish your goal, by simulating PWM through software.

Pro Minis are pretty good. Just because there’s more pins that doesn’t mean the ATmega328P uses a ton more power than an ATtiny85. With proper power reduction they should be pretty even with each other.

It's not just the CPU itself, but the supporting HW on a typical board, i.e. caps, resistors, regulators, serial chip, etc. I don't have specs but I'd be surprised if the tiny uses as much as the mini. Plus, it's not just current draw, but physical size. Some projects call for the smallest possible size.

habanero: It's not just the CPU itself, but the supporting HW on a typical board, i.e. caps, resistors, regulators, serial chip, etc

An Atmega 328 on a piece of veroboard will work at 8MHz with 3 x 0.1µF caps and 1 x 4k7 resistor to tie the reset HIGH.

...R

habanero: It's not just the CPU itself, but the supporting HW on a typical board, i.e. caps, resistors, regulators, serial chip, etc. I don't have specs but I'd be surprised if the tiny uses as much as the mini. Plus, it's not just current draw, but physical size. Some projects call for the smallest possible size.

An ATtiny requires just as much supporting hardware as an ATmega.

I'll give you size though. That's a very valid consideration.

Robin2: An Atmega 328 on a piece of veroboard will work at 8MHz with 3 x 0.1µF caps and 1 x 4k7 resistor to tie the reset HIGH.

...R

OPTIONAL: Crystal + 2 load capacitors.

Look into the Adafruit Wearables. They have very tiny Arduino compatible processor boards and other electronics intended for jewelry.

As far as batteries are concerned you may be able to consider LIPos.

They can be had in postage stamp size 2mm thick and have a high capacity.
You will have to consider the safety aspect od use in clothing though.