The Arduino AA Undershield

I recently bought an ArduinoDiecimila 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 AdafruitWaveshield 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.

Step 1: Get the Parts

Here is a list of the parts, you'll need to make an AA Undershield.

• A prototyping PCB that has the same size as your Arduino board.
• A battery holder.
• A MAX756 Integrated Circuit. There is a lot of boost converters out there, but I used the MAX756, cause I had a couple of them lying around.
• A 8 pin IC socket
• A 22uH coil.
• A 1N5817 or 1N5818 schottky diode.
• A 220uF Electrolytic capacitor.
• A 100uF Electrolytic capacitor.
• A 100nF Ceramic capacitor.
• A 100kohm resistor.
• A 110kohm resistor (I didn't have one, so I connected a 10k and a 100k in series).
• Two spacers to make space between your Arduino board and your shield.
• Two screws for the spacers.
• Two nuts for the spacers.
• Four spacers to make space between the undershield and the surface, you're placing it on (These are only needed if you choose to mount your battery holder underneath the shield).
• Four screws for the spacers (These are only needed if you choose to mount your battery holder underneath the shield).
• An Arduino or Freeduino board. I used a Diecimila, but it should work with the other boards just as well.
• Two AA batteries.
• An on/off switch (optional).

Step 2: Drill the Holes in the PCB

In this step, I'll show you where to drill the holes in your PCB. Start by placing your Arduino board on top of your prototyping board. When you buy a new Arduino board, it comes with two mounting holes. mark those holes on your prototyping PCB using a pen or permanent marker. then drill the holes. I used M3 screws (M3 means that they're 3mm in diameter), so I used a 3mm drill.

If you choose to mount the battery holder underneath the shield, you should drill 4 holes in each corner of your PCB for the spacers.

Step 3: Start Soldering

It's time to solder all the components to the PCB. I've included the schematic and some pictures. It's a good idea to start with the 8 pin socket, cause then it's easier to get an idea of where the other component should be mounted. You'll probably have to mount the two electrolytic capacitors and the coil horizontally, so that they're not taller than the spacers, you use to mount your Arduino with.

When you're done soldering, check your your circuit for mistakes. If you didn't find any mistakes, then hook up your circuit up to the batteries and a voltmeter. You should get around 5V and it should not be higher than 5.30 volts or lower than 4.90 volts.

Step 4: Mount the Battery Holder

It's time to mount the battery holder. There are 3 ways of mounting the battery holder. You can choose not to mount it at all and just let it dangle around, you can mount it beside the shield using a popsicle stick (this will of course make it wider) or you can mount it underneath the shield (this will of course make it taller). I chose the last method. You can mount it either with screws or hot glue. When you've mounted it, solder the red and the black wire in the right places (see the schematic in step 3).

Step 5: Mount All the Spacers and Your Arduino Board

It's time to mount all the spacers to the shield and mount the shield and the Arduino. Start mounting the spacers that is placed between the shield and the surface, you're placing it on. You should also solder two wires from the output of the shield (I recommend, that you use a red and a black wire to avoid confusion). When you've soldered the wires in the right places, use a voltmeter again to check the voltage.

Then mount the two spacers for the Arduino board.

After you've done that, it's time for mounting the Arduino board on top of the shield using two screws.

Then insert the positive wire (in my case the red one) into the place in the power header that is marked "5V". Insert the negative wire (in my case the black one) into the place in the power header that is marked "Gnd".

Step 6: You're Done

Congratulations. You've just made an Arduino AA Undershield.