Ultimate Portable Power Source: Axim, PSP, and USB All-in-one Charger




About: I finally graduated from Missouri University of Science and Technology (Missouri S&T, formerly University of Missouri Rolla) with a computer engineering degree. Originally from Belleville, IL (St. Louis are...

My first Instructable described how to build a compact power source that could power a Dell Axim PDA off of 8 AA batteries for extended use on long trips. It used a simple 7805 regulator and a few capacitors to filter the power. It could also be used to power a PSP, since both the Axim and PSP have the same adapter port and use the same voltage.

However, when I finally got to go on a long trip, my friend asked to borrow my charger for his PSP but accidentally hooked the connector up to the 8AA pack backwards. This pretty much fried the 7805 chip, rendering the whole thing completely and totally useless. Although I didn't get to watch movies on my PDA coming home, this led me to create a new design, one that would:

A) Protect against backwards connections so that simple accidents such as this wouldn't damage it
B) Provide power for USB charging devices (like the iPod, Sansa, etc) in addition to PDA/PSP
C) Provide 2A of power instead of 1A, my PDA running on full speed/brightness with WiFi and Bluetooth on apparently used more than 1A (7805 = 5v at 1A) and it would stop charging

To do this, I decided to add a diode at the beginning of the circuit (diodes only allow power to flow in one direction, preventing the backwards flow that destroyed my previous model). To accommodate 2A instead of just 1, I added a second 7805 chip in parallel with the first one. Since each chip provides 1A, 2 of them provide 2A. I also pulled some USB connectors off of a dead USB hub and added one to the circuit so that I could plug iPod/Sansa/other USB charging devices into it and charge them on the go.

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Step 1: Gather the Parts

If you've seen my first Instructable, you'll notice that this parts list is very similar, but some things have been added:

RadioShack Components:

1 - 2A Diode (They didn't have 2A so anything greater than 2A works also, I used a 3A diode)
1 - 100 uF Electrolytic Capacitor
1 - 0.1 uF Metal Film or Polyester Film Capacitor
2 - 7805 5 Volt, 1 Amp Regulator IC
1 - Project board (make sure you get the one with the pictured configuration)
1 - AdaptaPlug Socket with solder-on wires
1 - AdaptaPlug connector that fits your 5v device (for Axim X50v and PSP, that's an AdaptaPlug B)
1 - 8AA Holder with "9 Volt Terminals" (it should have the 9v-style connector on top)
1 - Pack of 9v-style connectors (optional, you can obtain one from a dead 9v battery if you want)

1 - Dead 9v Battery (for case and possibly connector terminals, the actual battery stuff isn't used and so I recommend using a dead one)
1 - Broken USB Hub or other device with USB ports (this is where we get the port, so obviously it will get taken apart, don't use a working device for this!)
8 - AA batteries (preferably NiMH Rechargeable) to power the thing with

- Digital Multimeter (or Analog Multimeter, this is used to test voltages, if you really REALLY trust your work, you can skip this, but I'm not responsible for you blowing up your devices because you didn't check your work first!)
- Soldering Iron (I used a 30W one from RadioShack) and Solder
- Desoldering tool (trust me, you'll need it...I'm pretty good with a soldering iron but I still make mistakes every once in a while)
- Small screwdrivers and pliers (used to pry the 9v battery case apart and extract the useless insides, leaving a usable project case)
- Scissors, clippers, or wire cutters/strippers (you'll need to cut/strip wires and clip off component leads)

Step 2: Test the Parts

This step isn't absolutely necessary, but if it's your first time building one of these (or anything similar), you'll want to know that you got the right parts and everything checks out. First, hook your electrical tester up to your 8AA pack loaded full of AA batteries. It should read near 12 Volts (WAAAY too much to feed to your PDA, iPod, PSP, phone, etc...it'd burn it out instantly). Then, connect the POSITIVE output of the 8AA pack to the LEFT lead of the regulator, the NEGATIVE output of the 8AA pack to the CENTER lead of the regulator, the NEGATIVE output of the 8AA pack to the BLACK wire on your multimeter, and the RIGHT lead of the regulator to the RED wire on your multimeter. It should read right around 5 volts (usually within 0.1 volts is good). Repeat this for both regulators. I recommend 20V setting on most multimeters.

Step 3: Take Apart the 9v Battery!

This isn't as dangerous as it sounds. You can safely pry the case off of a 9v battery and use it for a project case. The actual battery is contained within a plastic box (or some 9v's have 6 AAAA batteries in series). I used a small screwdriver and a pair of pliers to remove the insides. Keep the top and bottom plastic pieces (the black end caps), these will be reused for the case.

Step 4: Take Apart the USB Hub!

If you want to add USB charging capabilities to your pack, then you first need to obtain a female USB connector. You can buy these online, but my friend gave me a broken USB hub that he didn't need, so I just pulled some connectors out of it. You'll NEED a desoldering tool of some sort for this, as you have to remove the solder on the connector to get it out. You'll also probably want pliers and maybe a screwdriver to pry it off. The first one I took off was so stuck in the board that I took a hammer to it (ended up destroying 2 surface mount chips, but the board is useless anyways, so big deal...) though the second one came off nicely.

After that, trim off any solder tabs used to hold the port in. Then take a small wire (preferably a cord with two wires in it, so you can have both positive and negative in one cord, but if not you can just twist two single wires together). Looking at the port from the front, the plastic part should be to the TOP of the connector, with the metal contacts facing down. There will be four contacts, the one on the left is POSITIVE (5 Volts) and the one on the RIGHT is NEGATIVE. The two in the middle are for data, but this is a charger, so we will ignore these. Solder the wires to the back of the port on the left and right connectors, noting which one is positive and which one is negative.

Step 5: Prepare the Base

Before soldering the USB port and the Adaptaplug socket to the board, you'll want to feed the wires through the bottom of the 9v case. To do this, you'll need to make a hole in the lower cap of the 9v case. I couldn't find the drill, so I just took a nail and hit a hole in the cap using a hammer. After that I used a pair of scissors to scrape out the edges until it was big enough to fit both sets of wires through. Put the connectors (Adaptaplug socket and USB port) on the textured (outside) side of the cap with the wire ends on the un-textured (inside) side of the cap.

Also, I used electrical tape to cover my USB port and protect the wiring from being broken by handling.

Step 6: Solder Away!

Now you can begin assembling the circuit. Below I've posted a schematic diagram, a circuit board layout diagram, and a bunch of pictures of me assembling it. Be sure to keep your board compact and your solders clean, as that will help when you are trying to cram it into a 9v case.

In the last picture, the BLACK wires are POSITIVE while the plain RED wires are NEGATIVE (yeah, it's backwards from normal, but I didn't look when soldering them to the connectors and got it backwards). For the AdaptaPlug socket, look for the word "Tip". Face that mark towards you. The wire on the LEFT is POSITIVE, the wire on the RIGHT is NEGATIVE. On my socket, the left wire has some words on it, so the words also indicate positive (when attaching the AdaptaPlug B connector, line the "+" to the "Tip" mark because the Dell Axim power pack indicates that the Axim is "plus tip" where the tip (inside portion) of the connector is positive while the outer ring is negative.

Step 7: Cut It Out!

I built my circuit in the corner of a larger board. Since that obviously won't fit in the 9v case, you'll need to cut the built section of the circuit out of the rest of the board. I used a pair of scissors and a hacksaw to cut around the board.

NOTE: Scissors cut it fast, but, in my experience, whatever is to the RIGHT of the scissors as you're cutting gets destroyed (in this case, it was just the edge of the board, so no big deal) The hacksaw cuts much more cleanly but takes FOREVER to cut. I recommend using scissors on the outsides of the board and the hacksaw on the cuts inside toward the middle of the board. Be sure not to hit any wires or components with cutting tools. I scraped the side of a regulator, but not enough to cause any damage to it (the outside of them is just plastic).

Step 8: Tape It Up!

The 9v shell is made of metal. Metal conducts electricity. If you stick a circuit board with metal connections into a metal shell, the circuit will be rendered useless. So...we need to insulate the board. This is easy, just take a piece of electrical tape or duct tape and put it over the connections on the bottom of the board. I put a few layers to make sure that leads wouldn't poke through and short out. Then I wrapped a piece of tape around the top of the board to hold all the wires in place and to protect the metal tabs on the regulators. After that, you should be able to fit it into the battery case, if not, then go back and file down the solder joints to reduce height.

Step 9: Make a Cover Plate

To cap off the battery case, you'll want to make a top plate. I used the cardboard remains of the RadioShack packaging for the regulators. Take a pen and sketch the size of the first cap (the bottom one) on the paper. Then cut out the cover, but cut outside the lines (make it a bit larger than the original). Then size it up by holding it to the top and trim it as necessary. Then cut a slit halfway up (for the input wire to go through).

Step 10: Put It Together!

This is where it all comes together. Take the case, and stick the USB and Adaptaplug in the top (the part you bent open, the wires should come out the bottom of the case). Then push the board all the way in. After it's in, test it to make sure it isn't shorting out anywhere (nothing beats having to take it all apart again to retape it). Now stick the paper cap on the input wire and use electrical tape to secure the cap and close the cut part of the cap. Then use pliers to bend the metal case back over the cap. If it isn't completely secured by bending it back, cover it in tape to close the end.

Step 11: Test It Out!

Now it's pretty much done. You can paint it, color it, put stickers on it, cover it in electrical tape, or whatever else to improve its appearance, but from here on it is ready to hit the road and power your devices! You'll want to make sure it works first, so plug it in and test both the PDA/PSP connector and the USB port.

I used my Axim and an Xbox 360 controller. You can't charge wired controllers (obviously) but if the lights blink that means it's getting power.

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    53 Discussions


    1 year ago

    This is an approach I had been considering, but basically everybody is advising against putting 2 LM7805 regulators in parallel because the current draw might not be the same and each LM7805 in principle is also backfed by this circuit.
    It probably will work safely as long as you stay at lower currents, but It is not something I think could safely deliver 2 or 3 Amps and thus one might as well stick to one LM7805.
    Also a 9 Volt battery to produce 5 volt might not be the most efficient choice.
    I realise this is a rather 'old' instructable. Nowadays there are fairly cheap LM2596 based buck regulators that can deliver 2-3 amps with minimal loss

    I think the DS handhelds use 5V to charge, so yeah this would work, but the only way to get a DS charging plug is to cut it off of a DS power brick. They don't use USB or any other common connector.

    o thank and yea there are usb charger for the ds so yea i am going to built it but can you send me a diagram were i can use 4aa rechargable batterys? please!!!


    8 years ago on Introduction

    why did you use rechargable batterys and not your "zombie" batterys :P :P :P :P


    9 years ago on Introduction

    so that's why u used a 9v battery shell instead of shrink tubing....
    the wire assembly is too big, right?

    1 reply

    Reply 9 years ago on Introduction

    I used the 9V battery shell because I was housing a full PCB with 2 fairly large regulator IC's, a diode, and two capacitors, it would be a bit too big for shrink wrap and I wanted a more durable casing that would protect the PCB a bit more. The metal battery shell also absorbs a bit of heat from the regulators as they do burn off a lot of heat.


    11 years ago on Introduction

    I have a Sansa View mp3 player that I would like to recharge on the go. I have to plug it into the computer via usb cable and it uses 5 volts at 500 mA. How exactly would I need to modify your charger in order to suit my power needs?

    3 replies

    Not sure, my friend has a Sansa that charges fine using the USB port as is. You MAY need to use resistors on the data lines, check some other Instructables (iPhone/iPod chargers for instance) for the circuit (you can still use the 7805 though, you won't need two of them).


    Reply 10 years ago on Introduction

    You should be able to solder the two data lines together, and it will give the device acess to draw 500mA. Though going with the resistors is probably safer.


    9 years ago on Introduction

    Thanks for the great instructable. My Axim is charging allright with your design but the 7805s do indeed get ridiculously hot. I guess, I'll have to put heatsinks on them. Even with 6 AA batteries they still get very hot.
    Aren't they wasting too much power?  Is there another way to keep them cooler while using the batteries more efficienty?

    Yes, all you really need is the 7805 by itself, the capacitors are just for filtering power spikes and the second 7805 is only needed if your device draws a lot of current.  The diode is important as it protects against backwards connections, if you use that design you have to be absolutely sure that nobody will EVER connect the input power supply backwards else the 7805 will be toast.  The most basic "safe" design would be a diode and a 7805, put the diode on the positive input.  The 7805 requires more than 5V to produce 5V but I'm not sure what the low limit is.  It should probably be able to take anywhere from 7V to 20V or so, our robotics team uses a similar regulator with a 24V battery system but we have a heatsink and fans to cool it off (gets ridiculously hot).

    Thank you for your quick reply.  I am going to use this with solar so I was going to put diodes in anyway. 

    P.S. Robots are awesome, I have experience with the lego mindstorms, but I am fairly new to electronic (that are more complicated than switches, lights, and motors. 

    Thanks Again

    For just USB you mean? This isn't the best solution for USB as USB only requires 500mA (half an amp) and this is designed to put out 2 amps. While this will work with USB, the extra regulators will just waste power, burning it off as heat. The simplest thing to do with USB is to use only one 7805 regulator. This will still require over 5 volts for input but is simple. You can also use a switching power supply like the Minty Boost to get USB 5V out of only 2 or 3 batteries.


    10 years ago on Introduction

    will these work with 2 9.6 battery or at least 1 ?????