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

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

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.

Step 1: Gather the Parts

Picture of 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

Picture of 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,'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!

Picture of 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!

Picture of 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

Picture of 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!

Picture of 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!

Picture of 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!

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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

Picture of 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!

Picture of 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!

Picture of 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.


diy_bloke (author)2017-10-21

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

kartik negandhi (author)2012-06-13

wat if i use a 12v gaston battery or a 9v battery????

Andrew_48 (author)2011-06-01

can i use this to charge a nintendo dsi? please answer my question !!!!


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!!!

Andrew_48 (author)2011-05-30

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

kbhasi (author)2010-10-16

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

CalcProgrammer1 (author)kbhasi2010-10-16

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.

Solderguy (author)2008-10-15

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?

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).

mweston (author)CalcProgrammer12008-11-01

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.

Solderguy (author)mweston2010-05-29

What value would the resistors need to be?

hedgehog37 (author)2010-03-28

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?

imakethings (author)2009-12-16

can i use it with 6v power supply?

JaredsProjects (author)2009-11-06

Will this schematic work, also how much voltage do I need. 

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

ideas from no where (author)2009-06-13

can you give me a diagram w/o the PSP or PDA charger

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.

BC-45 (author)2009-01-30

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

CalcProgrammer1 (author)BC-452009-02-04

You can use anything from like 7.5V to like 20V, best thing to do if you're using 9.6V batteries (2 of them) is to wire them both in parallel, that way it can supply more power (and last longer).

I didnt know doing it in parallel would be better! Thanks a bunch! That should save me a lot of charge time. I've been lining up a 9v and a bunch of AAAs in series for my version.

biggyeyes (author)2009-02-04

dude, it's me, and hell it's working now albeit no LEDs xD now I just gotta build a step-up circuit so that I'll only use 2-4 AA/AAAs instead of a bunch of combined batteries. btw, I used a 1uF cap instead of a 0.1uF cap which you recommended to be placed in the last part of the circuit. Will that be alright?

biggyeyes (author)biggyeyes2009-02-04

btw, about the battery source. Since I'm using two 7805s, will I need 7.5v*2 (15v) to power both of them up properly or two sets of 7.5V bats in parallel? Because I just reread your previous comments, and I got confused with this since I remember reading somewhere that I need 15V to power both of them up. I'm just studying electrical physics and I know that parallel circuits only change in current but not in voltage. So the two 7805s should still get 7.5v despite the parallel design? I'm really confused, because I got this problem of connecting just one 7.5V battery pack or two in series when the input of the charger is accepts only one connection.

No! You need the same voltage, it just eats more power (amps). This means the batteries will drain faster. If you want to do anything, putting batteries in parallel would be better (doesn't increase voltage, just power). Anyways, a step-up is a VERY BAD IDEA for this project, as it consumes much more power than say, the MintyBoost. If it even were able to step up enough power, the batteries would be drained in a matter of minutes. This is a project where you're best off sticking with the big batteries.

biggyeyes (author)2008-11-16

dude, hi it's me again. I just finished the circuit --- it looks like the image above. But I have a problem, my PSP doesn't charge. My friend broke my multimeter so I couldn't test it. I think it's the LED that's making it not work. Btw, the circuit I made doesnt have the green LED in the end as the diagram shows. I used a new 9v battery as the power source. Is the LED that's causing the problem? Please help, thanks! I don't wanna remove the led only to find out it's not the problem because the circuit is so small i don't want to resolder all of them again

My circuit doesn't have any LED's... First, a 9V battery will drain REALLY FAST with this circuit. 9V's aren't meant for high current applications (as such, they are usually only found in flashlights, smoke detectors, small radios, etc). It should work, but the battery will die quickly, especially with the 2A system running. You should only need one 100uF capacitor, just put it across the DC input lines (just after the master switch should work). Make sure to line up the positive and negative lines of the capacitor to the positive and negative lines of the input. You don't need any capacitors after the regulators, though you may want to put a 0.1uF at the very end (right before the output to USB/plug). I did in mine, but it really isn't necessary. If you want to use LED's, remember to use resistors with them. I'm not sure what kind you'd need, but LED's usually burn out at 5V if you don't use a resistor in series with it. Also, you don't need two switches on the second regulator, just one at the front of the circuit will do, the second switch after the regulator is unnecessary. Make sure you get the polarity right before connecting to your PSP (make sure the positive and negative lines from the circuit match the ones on the official power brick or adapter). I doubt the LED is the problem, though if you're not using a resistor, the LED may have burned out.

ah, thanks man. I'll be trying that when I have more time. But the PSP still won't charge with a fully charged 9v battery running using a single 7805. My old charger (a simple battery>7805>USB circuit) worked. I'll be making it again using your directions but with no LEDs to simplify he circuit. Again, thanks a bunch!

You should probably test your 7805's. Just hook them up without any extra stuff (just battery to 7805 to PSP) and make sure it charges. If not, you may have gotten a bad 7805 or accidentally fried it while building the circuit. 7805's are sensitive to reverse-connecting and will break if you hook them up backwards.

biggyeyes (author)2008-08-28

Nice I didn't know two 7805s would yield 2A, I thought they would still yield 1A both. Anyway, if I connect a 1A device it would still be ok right? Because right now I have a very simple charger. Battery > 1x7805 > USB Would it be alright if I connect another 7805?

It's basic electrical physics. A series circuit increases voltage (two 1.5V batteries in series gives you 3V). However, a parallel circuit increases amperage (current). If one 1.5V battery could provide 500mA, connecting two of them in parallel would still yield 1.5V, but devices could use up to 1A instead of just 500mA (0.5A). You can't wire 7805's in series, though, because they have a dedicated input line meant to be connected to the initial power supply, but connecting the outputs of two 7805's together will double the current, yielding 2A. Current is an availability thing, a device that uses 250mA will only use 250mA no matter if it's connected to a 250mA power supply or a 5A power supply. The extra power will only be utilized by devices that need it. Voltage doesn't act this way (putting 12V through a 5V device will certainly fry it) but current does, so don't worry about higher amperage. However, USB is only 500mA. Connecting another 7805 will only make the battery pack die faster (7805's aren't 100% efficient, they actually consume a lot of energy just to convert, so using 2 7805's is half as efficient as using just one, I did it because I had to, but otherwise 1 is recommended). If you're just charging 1 or 2 devices at a time, then 1 7805 will do, if you plan on making a USB charger to charge 3 or more devices, you may want to use 2 chips. You could also put a switch on the input line of the second 7805 to turn it off when you're not running under full load (saves power because the second 7805 won't be drawing any power).

Ah, nice to know :D Haven't finished physics yet, still in projectiles, torque and everything. I was thinking of 2A or 3A because my PSP won't really charge properly with just 1x 7805. My PSP's charger gives 5V at 2800mA (2.8A). That means that my PSP is only receiving 35.71% of what the A is supposed to be. And by the way, just to make things clear, is the diagram correct? I didn't put the capacitors and crap in.

Yeah, that's right. The parallel circuit is correct. If you were to try 3 of them, you would add another one in parallel. With three of them it may get really hot, so you may want to consider some sort of heat sink, and you'll probably want a larger battery pack (or maybe a battery pack that uses like 12AA's with two sets of 6 in parallel, as parallel will increase runtime).

Gonna build one now. Thanks a bunch!

Thundertydus (author)2008-08-27

couldnt i jst take an ipod cord , cut it in half and feed the 12v battery cords and solder them then tape them together and plug it into my ipod?

No, cause iPod (and anything else USB) uses 5 volts. Feeding 12V directly into your iPod would fry the charging circuit and render it totally useless. The regulator circuit makes 8 to 18 volts or so into a steady 5 volt supply.

Unless the iPod is a FireWire one or the cable is firewire xD (read it somewhere here in instructables)

Diskun (author)2008-08-15

AWESOME! Just what I needed. But I could use some tweaking. I want to plug this power pack to a HTC Diamond PDA/Phone, the wall charger output is 5V @ 1A (battery is 900mAh, so I think I don't need two voltage regulators or 8 batteries. 4 of them and just 1 IC, and the whole thing would fit into a black project case I have around here. Much more portable and fancy :P So here's the big question: - Which modifications would I have to do to the circuit? Thank you so much p.s. Is it possible to integrate a quick battery charger to get an all-in-one portable power pack?

CalcProgrammer1 (author)Diskun2008-08-15

Simply remove the second 7805 chip. You'll only get 1A out of it, but most smartphones these days aren't as complicated as the Axim and don't need as much power. You'll need to find the right kind of plug for your phone, but other than that, just use the circuit described here.

However, I use 8AA batteries because it puts the voltage high. 4 might not be enough to make the regulator work properly, as 4*1.2=4.8 (too low to regulate, but enough to power your device without a regulator) and 4*1.5 (alkaline) = 6 (too low to regulate, but too high to use without a regulator). I would suggest at least 6 batteries to make the 7805 function properly.

Just remember the diode and you'll be good, the capacitors are filtering components, but since batteries have a fairly stable output, they really aren't totally necessary. I put them in just to be sure.

Diskun (author)CalcProgrammer12008-08-15

Nice. So... using more 2100mah @ 1.2V batteries will make any difference in stamina? I guess they do, but I'm not sure if it has something to do with the 7805. Excuse me if I sound stupid, I'm not too much into the theory, but I enjoy playing around with my soldering iron and some wires :P

CalcProgrammer1 (author)Diskun2008-08-28

If we assume that the voltage drop in batteries stays constant (the time that 1 battery takes to go from 1.2 volts down to nothing), then yes, more batteries should mean longer runtime, as the voltage going into the circuit will stay above 8 volts (the minimum input that the 7805 can make 12V from) longer. A better design would be to use like 9V supplies in parallel rather than a bunch of batteries in series, but this was easier to get and use.

Diskun (author)CalcProgrammer12008-08-16

p.s. I have just drawn a schematic of my "new" circuit over a "virtual project board". I haven't slept over the past 20 hours so I'm a little dizzy, but I think I've made no mistakes. I removed one of the ICs as well as the AdaptaPlug cables, as the HTC Diamond uses a Standard Mini-USB for recharging. Besides, they don't sell AdaptaPlugs here. See the attached image.

CalcProgrammer1 (author)Diskun2008-08-16

Yes, that will work.

Yerboogieman (author)2008-08-14

The 7805 already has a diode built in to it. otherwise, good instructable.

Apparently the one I used last time didn't. My friend hooked it up backwards and it wouldn't work anymore. On the multimeter, it still put out 5 volts, but apparently very little amperage (wasn't enough to even trigger the charging state in either the PDA or PSP). However, my new one has been reverse connected many times (on purpose) and it doesn't affect the 7805's, they just keep on working.


What about 300mA? The 7805 is supposed to regulate 1A (1000mA). The Axim's power supply is 2600mA (2.6A) so I used 2 7805's to regulate 2000mA, enough to fully power the Axim (even when CPU is on full, WiFi, BlueTooth, LCD brightness, playing video over the Internet, and charging internal battery). The first version would cut out if everything was on at once.

robots199 (author)2008-07-08

Nice Fake iPod, Looks pretty convincing!

Lol, it's a cheap fake from China (my dad went there for a business trip and found it for really cheap). Apart from the obvious iPod logo on the front (which real ones don't have) and plain USB connection, it LOOKS much like a 1st gen Nano, but the interface is horrible so I don't use it much, instead I use my PDA.

tagasadiko (author)2008-06-22

hi, im interested with that gadget youve made, i want to assemble the same version, can you pls e mail me the whole procedure w/ diagram @ thanks and more inventions:)

About This Instructable



Bio: 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 ... More »
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