Picture of The Arduino AA Undershield
I recently bought an Arduino Diecimila board. It's awesome and the applications, you can use it for or with is almost unlimited. However there's a problem when you want to use it in portable applications. You can use the Liquidware lithium backpack, which is a good way to power the Arduino. There's a problem with the backpack though, cause when the battery dies, you'll have to find an USB port or another external power source to charge it. You can't just replace the battery. You can also choose to power your arduino with a 9V battery and the built-in regulator of the Arduino board. The problem with this setup is that 9V batteries doesn't have a very high capacity, so they'll die faster.

That's why, I came up with the AA Undershield. It uses 2 AA batteries and boosts the voltage up to 5V, using a MAX756 IC to power the Arduino.

You may ask why I'm not simply using 3 or 4 AA batteries to power the Arduino. The reason why, I'm not using batteries to drive my Arduino directly, is that they're not regulated. Right after, you've recharged your battery, it may supply 1.4V, even though it's rated for 1.2V, so there's a risk of supplying your Arduino with too high or too low voltage.

Here is a video of the Arduino Diecimila and the Adafruit Waveshield attached to the AA Undershield. I've uploaded an example code, that changes the playback speed, when you turn a potentiometer. Other analog sensors will also work.

I apologize for the poor sound quality in this video. The mic in my camera is really bad.

The AA Undershield can also be used with many other 5V devices.
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wdieck6 months ago

Nice...this one does the same thing...just on top

nerd74732 years ago
this is so cool
wamj4 years ago
Is it possible to use two ''banks'' of batteries so that its possible to power the arduino for a longer period by switching between banks but keeping the same circuit
wamj wamj4 years ago
or would "D" battries last longer?
lloydrmc wamj2 years ago
D batteries would last WAY longer, though you can get 3000mAh AA's are easy to find cheap.

That being said, you could dispense with the switch and just wire the battery packs in parallel (plus to plus, minus to minus)
Chowmix124 years ago
can you hook up two max756s to have 400mA output? becuse im using motors... they will be better off with 400mA than 200mA
in parallel...
There are a LOT of similar chips available, even from Maxim, current capacity is up to 2A, some of which are even programmable for a lower current output.

I beg to differ on the minty boost LT chip, as availability is spotty at best.
Although I haven't tried it, I don't think you can. Instead you might be better off by using a newer regulator with a higher output current, such as the LT1302 which is the same one as the one used in the mintyboost USB Charger:
is there any that i can get from Maxim? I prefer them, and they generous with samples.
Another user, who said he was working for Maxim, said that there was a newer and more efficient regulator. He mentioned the MAX1674/MAX1675. By quckly looking over the datasheet, it seems that the MAX1674 is capable of up to 1A, while the MAX1675 is capable of delivering 500mA.
Did you use the mintyboost 1.2 schematic as a guide for this? Because the two resistors aren't necessary unless you are using an led for low battery signal on pin 4, which in your schematic isn't used.
The Linear chip is wayy nicer than the Maxim...
Hello there, is it any compatible IC available for the maxim? Because i can not find it in my country ...

Thank you in advance.
Cello623 years ago
  Done!! works fine. Thanks for this instructables.
Cello623 years ago
Nice project
You have a personal message. Help request.
robot7974 years ago
you sayd in the intro that you cant use 4 batery's but you can the arduinio has a 5 volt regulator build into it so it will be powered if the voltage is higher that 5 volts
I didn't say that you couldn't use 4 AA batteries to power your Arduino. All I said was that I don't recommend it and it's inefficient. The regulator on the Arduino board has a dropout voltage of 2Volts, which means that the input voltage has to be 2 Volts higher than the output. Since the output is 5V, the input must be 7V. Although you might be able to run your Arduino on 4 batteries with the built-in regulator it will be unstable and inefficient.
 is it possible to use IC 7805 instead of MAX 756??
 no, the 7805 needs at least 6v to start working, 7 is better,  the arduino already has a small 7805 on the board, linear voltage regulators like the 7805 waste energy, others, like the max756 save energy, so the batteries last longer, and you can use lower voltages, to achieve higher voltages!

2 x 1,5 = 3v

3v -> [MAX756] -> 5v
much better
appsman5 years ago
Let me start by saying I work at Maxim. Thanks for using our part. The MAX756 is fine for this, but you might be happier with a newer device like the MAX1675. it has a synchronous rectifier built-in (so no diode is needed), and better efficiency (about 93% instead of 86% at 100mA out). I probably shouldn't say this here ;-) but they (we) are pretty liberal with samples.
hi, for the newer max chip, could you use the exact same components? (apart from the chip ofcourse)
It looks like it. This chip might have another pinout though. Check out the datasheet. It has some example schematics:
Sorry, I forgot to say the pinout of the MAX1675 is different from the MAX756.
so, when you say a different pinout you mean the order of the pins? but otherwise this would still work?
Yes, the same parts will work, though you could get away with lower value caps if you want.
Thank you very much for the tip. I purchased the MAX756 at an online store along with some other parts, without doing any research on the efficiency of the different boost regulators.
andrew1015 years ago
how did you get arduino to play music? ive been looking on how to make it play a wav file, but everywhere says to buy the wav sheild or something dumb like that
is that what ur using?
Yes. I'm using the waveshield.
raykholo5 years ago
this seems to be a more customized towards arduino version of the mintyboost 5v usb power supply by ladyada on other thoughts, nice idea and adaptation
JAK1016 years ago
How much does all of this cost??? JW
yeah how much did it cost it is a good idear bit y not just get 2 of the arduino batteryholders in paralel so it does no halm to the arduino and plug it in the bottom of the arduions batery plug lol that would last longer with the same voltage and a usb plug so u can charge the batterys with a chargeing curcit so when u plug in the usb cable in u will charge the batterys for the arduino. lol that would be so good and easer to fit with an arduino mega as long as it doesnt need evan more power...
blalor6 years ago
Do you happen to have a link or part number for that protoboard you're using? I'm looking for something similar, but searching Jameco and Mouser for that kind of thing is a lesson in frustration. It's exactly what I'm looking for. Great idea, by the way. I have a small sample of these chips and the required components, but got hung up on the circuit board layout. One of the other benefits of using AA or AAA batteries is their ubiquity and that they're easily found as rechargeables. Most common solutions use 9v batteries, but they don't last terribly long, and very few chargers support them.
Artificial Intelligence (author)  blalor6 years ago
I bought the protoboard at a local electronics part store, where they sell Velleman kits and parts, so it's a bit expensive there, but this is the board that I used.
jeff-o6 years ago
Cool idea. You could use board-mounted AA holders and mount them directly to the PCB, so that you don't have an external battery pack dangling off the side.
Looks like a good idea. Have you thought about putting a 2.5mm plug on the power lines, so that it just plugs right into the Arduino external power jack? That way you don't have to plug it into the top shield(if you use more than 1, for example). I guess you would need to add more batteries to it to get the to 9-12v recommended voltage. Its a good idea, and I might to do something similar with my arduino.
You don't want to feed this sort of power supply back through a regulator. The MAX756 is outputting a regulated 5v in this case. The barrel connector is for power supplies generating 5v and up (to maybe 12v?). The USB port on the Arduino would take 5v (no further regulation is needed), but why add the extra parts to the "undershield" if it's not necessary?
Instead of using the 2.1mm "barrel jack", you could add a usb plug to the output and plug that in.