USB - we all use it every day.
USB allows to share all kind of data on a small USB-Stick, on every PC. Even big amounts of data can be carried on an USB Hard drive. And it' s a perfekt power soure for mobile devices eg. cellphones or MP3-Players.

But soon you'll spot the first problems. You just haven't enough USB-Ports to charge all your moblie devices. Hard drives need to much power for some PC's, most stereo systems and all USB-OTG(on the go) devises. It's Impossible to charge Ipods with a normal USB charger.

I was annoyed of all these problems, so I thought about a solution. I came out with this USB-stick-sized adapter. It should help you with all your USB power problems.
Mainly it has 4 functions:

1. Charge two USB-devices at a single port, while one is still connected to your PC/ other host.
2. Charge two USB-devices with an external power supply.
3. Take power from an external power supply to be able to run USB hard drives on OTG devices, stereo systems, ...
4. Charge your Ipod (I haven't on so I can't tell you if it works). This may even help to charge your moblie phone faster, but try it at your own risk.

Make sure you read the Important Information below.

Step 1: Important Information

FIRST: I'M not resposible for any damage to you and any devices that this adapter is connected to.

Read through everything (especially read bold and underlined words/phrases) before you start. Steps in [ ] are not nesessary for some functions. You can skip these steps if you want.

For this projekt it is very importent to work exactly. Even tiny mistakes can cause big problems. Reminder that whenever you work with USB. (or do you want to blow up your mainboard / phone / anything else ?)

This isn't an USB-Hub, so dont say " the second port doesn't work for my USB-stick". The second port just offers power to charge devices.

function 3:
If you want to run a hard drive at a OTG-device (in my case it's the S2) remeber it might just accept Fat32 which limits the size of one file to 4GB.
If you can check first if your hard drive runs with just power. Simply plug it into an USB charger and watch if the LED turns on or not. If the LED does't turn on (and your hard drive doesn't make the usual sounds) function 3 might not work.

I might have mixed up meanings of a few words (like port & socket) but I'm too lazy to correct it. That's it for now. Go on.

Step 2: Preparation: Blueprints

Let's spend some project-relavated thoughts:

Function Nr. 1:

We want to have one fully funktional USB-Port in any case. (power & data) So we have to connect the plug directly to one port. I figured out that too long traces (especially thoses which will be later used for the data) on the PCB cause problems. Have a look on step 7 to see how I did the PCB "layout". The second port needs just power so we can connect it to the + and - . So far so easy

Function Nr. 2:

In combination with Nr.1 very easy as well. Just solder a USB plug (male) to + and minus or solder an external power supply directly to the circuitboard. It would work, but only untill you decide to plug in the USB plug we've added for Nr.1 ...

Function Nr. 3:

... If you would do so you got two at least slightly different voltages conected to each other, what mostly will cause overheating of one powersupplys until the voltage regulater burned out. So I had to find another solution. First I thought about an IC to regulate both voltages to exactly the same, but that would be too complex, too expensive and too easy to make huge mistakes.
I solved the problem with a switch inside the power connector. If you plug in the external power supply it will disconnect mechanically the power form the USB plug exchanging it with its own. That's a loss of 500mA, but who cares if you replace it with 2000mA.

Function Nr. 4:

As you might know "normal" USB-chargers doesent work for ipod/iphone. That's because they "ask" the host controller before they take the power. I shouldn't mind because I haven't any products from apple, but I know many people would like a simple solution. On instructables I found this solution (https://www.instructables.com/id/Modify-a-cheap-USB-charger-to-feed-an-iPod-iPhone/) to charge iPod's / iPhones. In our case we would include the resistors to the second port which doesn't need the data lines. (step 10)

The final schematic is shown in the picture above. The circuit with included IPod charging function is shown in step 10.

Step 3: Preparation: Think About the Power You Need

First you have to find out how much power you need at the most.
So check your devices if you find information like "100mA". Sometimes you can have a look on the charger's output current eg. for cellphones. If you don't find any information, have a look on the List below.
Common values:

keyboard: 100mm
mouse: 100mA
USB-stick: >50mA
webcam: 400mA
cellphone: 400-1000mA
hard drive 2,5": ~900mA
fun gadgets: <1000mA?
other: >500mA

Add the values of two devises which might be used together.
eg. 50mA + ~900mA = ~950mA
Note down your highes result.

Note: Some combinations only work with a PC, like any with the webcam.
Note2: The second port offers just power, so just connect devices to charge (or to use the power in a differen way eg. a USB-LED, a USB-Fan, ...).

Step 4: Preparation: Materials & Tools

Tools:

a soldering iron & equippment (abot 30W or, much better, regulated)
a fine saw for metal
some files
a hotglue gun
carpet knife
a vice (you dont really need one, but it might be usefull)
a multimeter to check if everything works (important!)
some plires (alway useful)

Materials:

1 USB Plug (male)
2 USB Ports (female)(better one doubleport)
an external power supply
a matching socket with an internal switch (to detect whether the power supply is pluged in)(3 connections)
a circuit board with copper stripes (about 26,5mm x 16mm; 10 x 6 "holes" on an regular board; so there should be 6 stripes 10 "holes" long)
solder
hotglue
a few cm wire
4 resistors (just if you want to charge your ipod/iphone, I'll come back to it later in step 13)

"a large group of the people on this site don't understand exactly how electronics work" said XOIIO and he's maybe right. If you don't understand what is meant in the following paragraph and the reason why this projekt is nothing for you. (Serch for "regulated DC" if you still want to do this and inform yourself)
Missing knowlege can destroy your devices. I don't want to hear "blah blah blah you made me destroy my device" afterwards.

Let's come back to the power supply.
In the step before I told you to figure out how much power you need. 2A (2000mA) should be enough in (nearly) any case.
Make sure it's voltage is 5V (min. 4,65V - max. 5,25V) on every load (0,01A - 2A). To measure on differnt loads you can put a resistor between + and - ; eg. for a load of 1A you need a 5V /1A= 5Ohm . Keep in mind 5W (/10W) become heat so take a big resistor.

Where to get the stuff?

The simplest solution would be to buy everything from your favorite online store.
You can get (nearly) all parts for free by disableling old devices. You can get the USB stuff from a broken USB hub or any other USB device. I take the socket and power supply from a crappy digital picture frame I got for free.
Very common you get a USB Power supply with your phone, the dockingstation, ... But in this setup it doesn't fit to the power socket. If you want to use it read step 13.

Step 5: Preparation: Measurements

Now we have to measure the socket with an internal switch for the power supply.

1. Unpluged: Measure wich pins ar connected (resistance = 0 +- a few Ohm). Note that down. (Name the connections 1 - 2 - 3)
2. Plug now the power supply in an measure the voltage between all pins. Not that down as well. (Use the same names with + and - )
3. Now comes the most difficult part (to explain as well...)

If everything is gone right you should have written down 4 numbers, one number twice(if not you may have the wrong type of socket). This connection has to be later directly connected to yor USB ports (female) (to the + or the - line, just as you measured before).
The other connection ( + / - ) has to be connected to the USB plug and the ports.
The last connection has to be connected to the USB plug as well, but to the other power line (to the not connected one before)

Remember the numbers and connections for later or write it down.

Step 6: [Construction: Make the USB Doubleport]

You can skip this step if you have a doubleport allready.

If you have just like me only single ports go on. I use SMD ones (because they were lieing around) but you can use the normal as well.

The ports need a small distance from each other. Otherwise the other port would be blocked if you plug in a USB device. In my case they need an additional piece of the circuitbord inbetween. I just glued the tiny circuitbord ontop of the first port and the second on top of the circuitbord. Just like a sandwich. You might want to do it different, you can always compare it with the distance of the ports at your computer. Make sur the hotglue doesn't touch the contacts.
Now solder the cases together. This might be hard if you got a bad soldering iron. To make it easier you can prepare the soldering point with a file and sone soldering paste. (don't make a mess)
Solder the very left + wire to the left of the other port. If the origonal wire is too short expand it with a piece from your wire (but still try to keep all wires as short as possible). To make sure it won't touch the case you can put som hotglue between them. Go on with the very right - wire the same way.
Mesure the conections.
1. Both cases should be connected.
2. Both + wires should be connected.
3. Both - wires should be connected.
4. No data lines should be connected to anything.
If you find any mistakes correct them.

Step 7: Construction: Circuitboard

The "perfect" size is always as different as your parts are compared to mine, so figrure out the perfect position of the parts and and your perfect size first. Keep in mind to keep the traces as short as possible. Betwenn the USB plug and the USB ports should be at least one hole space, better two.

Now cut out your part. Don't try to saw between the lines, "sacrifice" another for better results. When you're done with this take a file and remove any sharp edges. If some copper at the edge (usually 1/4 of a line) is leftover, remove it with the file as well.

Try to place your parts again. Everything fits? Perfekt. If not, do some modifications.
If eg. the plug has too big conection wires of the case remove the part between two holes to create a bigger one.

Step 8: Construction: Solder the USB Stuff

Before you start turn the copper to the upside. You shoud solder on the surface to prevent fingers or other objects making a short circuit in use. Don't use too much solder.

First solder the USB plug to the circuit board including it's case. Now go on with the ports. Solder their case to the bord as well.
The last thing you have to do is to cut through a connection. Which one? In step 5 you shoud have figured out a direkt connection of the powerlins between the plug and the ports. Cut through the opposite one with the carpet knife.

Step 9: Construction: Add the Power Socket

Now you have to solder the socket to the circuitbord as you figured out in step 5. All sockets look a bit different so I can't give general instructions to mount it perfect, figure it out by yourself. But I've a few hints:

Most times USB plugs are much longer than needed so you can take some hotglue to stick the socket there.
Remeber to watch out for blank wires touching the cases of the USB plug/ports. To prevent short circuits correct those mistakes if you spot them.
Don't use too thin cable. Remeber power will later run trough them. I used 0.45mm wire but aunything above 0.25mm should be (hopefully) ok as well.

Step 10: [Construction: Make It Ready for the IPod]

Caffeinomane (https://www.instructables.com/member/Caffeinomane/) made a great instructable (https://www.instructables.com/id/Modify-a-cheap-USB-charger-to-feed-an-iPod-iPhone/) telling about how to charge apple devices such as ipod or the famous iphone. When I asked him to include the information here, he send me the following link where he got his information: http://www.ladyada.net/make/mintyboost/icharge.html

The solution is for the mysteries problem of non-charching devices is...
Sending exact voltages through the datalines. To get those 2 voltage dividers made of two resistors each are used. There are two ways to charge:

with full current (1000mA): 2.8 V on D- and 2.0 V on D+
with half current (500mA): 2.0 V on D- and 2.0 V on D+

Before you start to solder, try out the adapter with other devices to make sure everything works fine.

Because the space is very limited, you should try to get the smalest parts as possible; betwenn + and D- and D+ and - you could even solder a tiny SMD resistor. The values you need are shown in the pictures above. When you go an measure in the next step mind that you connected + and - with resistores (that means different results).

I've never tried this so I can't say if it works!

Step 11: Final Touches: Measuring

Now it's time to measure again!
If you find any problems, try to solve them.
Mind the resistors you might added to charge your IPod alter the results, so read step 3 and 4 instead of 1 and 2 if you included this feature.

1. Keep it unplugged. Just measure the USB Ports. (without IPod charging option)

Put your multimeter into continuity testing mode / resistance measuring mode.
All " + " had to be connected directly (0 Ohm) to each other and mustn't be connected to anything else (infinit Ohm)
All " - " had to be connected directly (0 Ohm) to each other and mustn't be connected to anything else (infinit Ohm)
The datalines of the plug (male) had to be directly (0 Ohm) connected to the opposite USB port and mustn't be connected to anything else (infinit Ohm)
The datalines of the upper USB port mustn't be connected to anything else (infinit Ohm)
The cases had to be connected directly (0 Ohm) to each other and mustn't be connected to anything else (infinit Ohm)
This shoud be it (I hope :)). Go on.

2. Plug in the external power supply. Just measure the USB Ports. (without IPod charging option)

Put your multimeter into voltage testing mode.
Between the " + " of both USB ports and their and the plug's " - " you should measure 5V +-0.2 and to anything else you shoud measure nothing
Between the " + " of the USB plug and anything else you shoud measure nothing.
Doublecheck their's no voltage on the datalines
You're done with measuring.

3. Keep it unplugged. Just measure the USB Ports. (with IPod charging option)
Resistences for D+/- are just for the upper USB port, the datalines of the other ports belong to "other"!
I took the values from (1.) fast charging for the calculation.

Put your multimeter into resistance measuring mode.
All " + " had to be connected directly (0 Ohm) to each other, connected through ~53,84 KOhm to " - " , ~34,6KOhm to D-, ~49,43KOhm to D+ and mustn't be connected to anything else (infinit Ohm)
All " - " had to be connected directly (0 Ohm) to each other, connected through ~53,84 KOhm to " + " , ~39.18KOhm to D-, ~39.18KOhm to D+ and mustn't be connected to anything else (infinit Ohm)
The datalines of the plug (male) had to be directly (0 Ohm) connected to the opposite USB port and mustn't be connected to anything else (infinit Ohm)
The datalines of the upper USB port had to be connected like said above.
The cases had to be connected directly (0 Ohm) to each other and mustn't be connected to anything else (infinit Ohm)
This shoud be it (I hope :)). Go on.

4. Plug in the external power supply. Just measure the USB Ports. (with IPod charging option)

Put your multimeter into voltage testing mode.
Between the " + " of both USB ports and their and the plug's " - " you should measure 5V +-0.2 and to anything else you shoud measure nothing, except the datalines of the upper USB port
Between the " + " of the USB plug and anything else you shoud measure nothing.
Doublecheck their's no voltage on the datalines, except the datalines of the upper USB port
You're done with measuring.

Step 12: [Final Touches: Make Hard Drive Ready for OTG]

The very special thing about this is that you can connect harddrives to cellphones/ other USB OTG devices. If you would just plug it in your phone would commonly not recognize anything. That's because the phone uses just FAT32 but your hard drive will be formated in NTFS.
Important: FAT32 has a size limit of 4GB per data so you might have to split up bigger data.

You will need a program to change NTFS to FAT32. I used "EASEUS Partition Master 9.1.0 Home Edition". This free program might be not the best but it is good enough for now.

NOTE: During the progress data can get lost. So backup everything before you start!!!
The process might take long when there's still data on your harddrive. If you made a backup delete the origional partition and create 2 new ones (much faster).
Have a look on the pictures as well.

install
start go to main srceen)
either resize the partition or delete it to create "unallocated" space infront (Important!) of the other NTFS.
right-click on the "unallocated" space, "create partition"
fill out the gaps in the window:
1. partition label: Name it as you want
2. create as: primary (Important!)
3. file system: FAT32 (Important!)
4. drive letter is unimportant; change it if you want to. You can still call the NTFS part "F" and the FAT32 "G", if the FAT32 is infront of the NTFS.
"OK"
Press "Apply"
Copy the whole content back tho the hard drive
You're done :)

Step 13: [Extra: Take Power From an USB Power Supply]

To take the power from an USB power supply you can simply solder an adapter cable. USB plug (male) on one side the power plug matching the socket on the other. Simple and usefull especially for function #3.

Step 14: Let It Run!

Your're done (at least with reading :D). Congratulations!

Have fun and report your results, any occuring problems and your solution if you found one.
If you made a much better version of mine write your own instructable showing us the differences (When you publish it would be nice if you would inform me via PM).

If you spot somewhere a language mistake feel free to correct me. I'm still learning.

Don't forget to rate, comment and if you like this feel free to follow me or to share the link. This would help me a lot.
Thanks.

Introduction: Multi Purpose USB Power Adapter