Battery alternatives for Arduino project

Thread Starter

Terrypin

Joined Feb 5, 2016
113
My project is a music box controlled by a UNO and consumes about 100 mA when playing an MP3 track. It must be battery powered, and space limitations means these need to be AA. As there is unfortunately no 5V battery generally available (I’ve never understood why?) I have to choose between alkaline and NiMh. Alkaline means regularly opening the case and are expensive. NiMh would be more convenient and economical. But both raise questions of whether to use three or four batteries, and if the latter whether to drop the voltage with one or two silicon diodes, or perhaps two or three germanium types if I can find any in my junk box. Or maybe just a zener and suitable resistor would be OK?

I’m guessing other hobbyists have had similar choices to make and I’d much appreciate any tips, suggestions, recommendations, etc please.

Terry
 

dl324

Joined Mar 30, 2015
16,839
So you have space for 4 AA batteries and it's just the inconvenience of changing batteries that you're trying to avoid?

How long to you want the battery to last?
 

KeithWalker

Joined Jul 10, 2017
3,063
The ATMEGE328-PU datasheet states that it will work with a supply voltage from 1.8 to 5.5 Volts. It will probably not run at full speed at lower voltages but is should work fine for your application with four NiMH cells.
 

Thread Starter

Terrypin

Joined Feb 5, 2016
113
Thanks all, appreciate the fast responses.
As they are inexpensive, and as I’ve never used a ’buck boost’ before, I’ve ordered the product below.

I should have added that I’m keen to keep close to or just under 5V because the audio module I’m using, a DFRobot MP3 Mini Player, wants 3.3 to 5.0V (it’s optimum is 4.4). Most of the 100mA is to the 4 ohm miniature speakers.

With my bench supply the project seems OK at the levels I’ve tried so far, 4.5 to 5.1.

Brand: Yizhet
Yizhet 5 Pack Buck Converter LM2596 DC to DC Converter High Efficiency Voltage Regulator 3.0-40V to 1.5-35V Buck Converter Adjustable Power Supply Module[/SIZE]
 

Thread Starter

Terrypin

Joined Feb 5, 2016
113
4 x Ni-MH cells will be enough without the buck converter.
My experience is that four NiMh AAs are initially too high. That’s confirmed in various sources, such as this from wiki:
“Under a light load (0.5 ampere), the starting voltage of a freshly charged AA NiMH cell in good condition is about 1.4 volts.”

The load for my music box is about 30 mA initially or when no track was playing. And 5.6 V is above the absolute max of 5.5 V allowed for the 328. Dropping it with a silicon diode would take it to an initial safe value, but its useful life before recharging would then be significantly shortened.
 

djsfantasi

Joined Apr 11, 2010
9,156
Again, if you can get a supply of 7-12V to the Arduino, the Gnd and 5V pins can be used to power your “music box”. No other components are necessary.

The 5V pin supplies power regulated by the onboard regulator on the Uno.
 

Thread Starter

Terrypin

Joined Feb 5, 2016
113
If you'd tell us what volume is available for the battery, we might be able to suggest some higher energy density solutions...
Sorry for delay in answering. I'd been trying to suspend the circuit (which is on on veroboard) from the top panel (with its 11 buttons and two switches). Frustratingly harder than I'd expected. So I'm now using bottom of the case for both batteries and circuitry. Should finish that shortly and will post photo later.

But almost sure 4 x NiMH will be my choice, even in the familiar two-layer holder. With a jack barrel socket for charging conveniently via 5V USB cable. Still nervous about that initial 5.6V though. Might play it on bench with diode or small resistor until say 5.4V, before screwing on the panel and gift wrapping it.
 

Thread Starter

Terrypin

Joined Feb 5, 2016
113
Again, if you can get a supply of 7-12V to the Arduino, the Gnd and 5V pins can be used to power your “music box”. No other components are necessary.

The 5V pin supplies power regulated by the onboard regulator on the Uno.
Yes, although I think the UNO likes 9V plus. What other battery options do you have in mind?
 

Thread Starter

Terrypin

Joined Feb 5, 2016
113
My favorite is a AA 6 pack. I buy them by the dozen in Amazon.
Thanks, hadn’t considered that, but reckon I now have space. Even if I have to custom wire up several holders. Duly ordered.

Haven‘t checked but assume the UNO regulator is comfortable with brief excursions around say 200mA?
 

djsfantasi

Joined Apr 11, 2010
9,156
Thanks, hadn’t considered that, but reckon I now have space. Even if I have to custom wire up several holders. Duly ordered.

Haven‘t checked but assume the UNO regulator is comfortable with brief excursions around say 200mA?
The Arduino Uno regulator maxes out at 250mA. So you’ll be close if you hit 200mA, as the Uno needs a few mA. But you also have to account for everything else connected to the Uno. Total the current draw of each pin in use and add that to your total.

When powered by USB, it can draw 500mA, but this is the extreme case and it bypasses the regulator. I see typical maximums of 200mA. So you’re at the limit.
 
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