HOW TO MAKE USB OTG CABLE WITH AN EXTERNAL USB POWER SUPPLY for those who cannot find such a cable in their country(like me)
You need a kernel with USB OTG support. SebastianFM’s kernel, here
The Micro Usb connector has 5 pins inside. In standard data cables that comes with the phone, only 4 pins are used. When the unused pin is connected, the cable becomes an OTG cable.
Pin 1 : VCC pin, +5V Power supply, COLOR : RED
Pin 2 : D-, Data- Signal line, COLOR : WHITE
Pin 3 : D+, Data+ Signal line, COLOR : GREEN
Pin 4 : This is the pin which is not used in standard data cables, we will “SHORT” it to pin 5 to make an OTG CABLE
Pin 5 : GND, Ground Supply
These colors are UNIVERSAL in USB connectors, this means the red is always VCC, black is GND and the other two always perform the same action, unless somebody deliberately connects the colors to different pins 
Warning : I’M NOT RESPONSIBLE FOR ANY DAMAGE ON ANYTHING. (YOUR PHONE, DATA CABLE, USB CONNECTOR, HOUSE, FERRARI ETC.) IF YOU AVOID ANY SHORT CIRCUITS, AND COMPLETE ALL THE STEPS AS I EXPLAIN THERE WILL BE NO PROBLEM. AND THIS TUTORIAL SUPPOSES YOUR PHONE AS AN HTC PYRAMID
IF YOU ALREADY HAVE AN OTG CABLE, YOU DON’T HAVE MUCH TO DO.. YOU GO TO 2
1 ) THOSE WHO DON’T EVEN HAVE AN OTG CABLE START HERE -THESE STEPS REQUIRE EXPERIENCE ON SOLDERING
What you need:
1)A “MICRO USB B” head. (Can be obtained from an old charger, data cable)
2)USB A Male to USB A Female Connector : These Connectors
3)USB Cable (A short one is enough)
4)A sharp knife,etc.
5)Soldering Kit
6)Hot Glue
7)Tape
8)Some experience on soldering
STEP 1 – The first thing yo need to do is to SLICE two sides of the plastic cover of the micro USB connector, and clean the glue under it. You will need the plastic cover later!
HAVE A LOOK AT THIS VIDEO TO UNDERSTAND CLEARLY
STEP 2 – Once you reach the pins under the glue, you can get your soldering iron now to start soldering.
Matching cable Colors and Pin NUMBERS AGAIN : 1-RED, 2-WHITE, 3-GREEN, 4-NO CABLE, 5-BLACK
STEP 3 – If you did soldering (or cables are already soldered to pins–if you’re using a data cable) now you need to SHORT CIRCUIT the EMPTY PIN (PIN 4) and PIN 5 (Black Cable). You can use a very short piece of cable to do this. NOW YOU HAVE A “MICRO USB B” CONNECTOR WITH OTG SUPPORT.
STEP 4 – After you completed the soldering, and IF you are sure you made no mistakes, apply HOT GLUE. Wait for it to get cold and hard, then cover it with the plastics you sliced before. You can use cheap quick glues to do that. How the connector looks after all depends on your creativity and ability
STEP 5 – Cut the cable of the USB A MALE to USB A FEMALE connector at 20-25 cm from the female connector. Now you can connect USB Female A connector, Micro USB B connector, and USB Male A connector
STEP 6 – First connect the matching colored wires of USB FEMALE A connector and Micro USB B Connector (red to red-white to white-green to green-black to black). Now you’ve a working OTG cable, but without an external power connector.
STEP 7 – To connect the “USB A MALE” connector,which will be the external power to the OTG, you only need to connect red and black colored wires of it (the +5V and GND wires) to the matching colors of the other two cables you connected before (“MICRO USB B” and “USB A FEMALE”–The OTG CABLE you’ve made). If you connect white and green wires of “USB A MALE” connector, YOUR CABLE WILL NOT FUNCTION. DO NOT CONNECT WHITE AND GREEN WIRES OF MALE USB A CONNECTOR.
You can use soldering iron to strenghten the connection between wires. Or you can just use tape. It’s up to you. Just be sure that there’s no possibility of short circuits.
You need to use tape for each color of wires to prevent short circuits.
AGAIN : Be sure that you’ve made all the steps carefully and correctly, and avoided any short circuits before using your cable. The only short circuit should be the pin 4 and pin 5 of MICRO USB A connector
AND YES IT’S DONE, YOU CAN USE YOUR CABLE NOW
2 ) THOSE WHO HAVE USB OTG CABLE AND JUST WANT TO CONNECT AN EXTRA USB POWER CONNECTOR–START HERE
You need :
1)MALE USB A CONNECTOR with 100-120 cm cable — lenght depends on you, should not be much longer than 2 meters(standard usb connectors) (U can get it from any data cables, old USB mouse cables, controller-joystick cables.. Just cut the cable at 100-120cm from the connector)
2)Your OTG Cable
3)A Sharp Knife etc.
4)Tape
5)Soldering kit (optional–if you want to strenghten the connections of wires)
STEP 1 ) Cut the USB OTG cable in the middle.
STEP 2 ) You only need red and black colored wires of “MALE USB A” connector, which are +5V and GND.
STEP 3 ) Connect the matching colors of your OTG cable again, but this time also connect the “MALE USB A” connector’s red and black wires to the matching colors. WHITE and GREEN wires of this connector should not be connected. Otherwise the cable WILL NOT FUNCTION.
You need to use tape for each color of wires to prevent short circuits.
BE SURE THAT THERE’S NO POSSIBILITY OF SHORT CIRCUITS AND YOU’VE MADE NOTHING WRONG
You can also connect SHIELD WIRES of each cable to each other. But i’m not sure what actually it does. If you test it, please post your experiences.
What is Shield Wire:
The USB cables actually also have “SHIELD WIRE”. My 2.5″ external LG HDD does not work with the cables without shield wire, but many products should work. Shield wire is the one silver colored wire surrounding the other four colored cables and aluminium foil. It is connected to the outer silver colored parts of the connectors. I’ll update this post after testing if shield wire needs to be connected,too. For now i use my cable without it, but my hdd does not work. All others (usb mouse, usb flash drives, joystick, hub, my sony e443 Walkman , PS3 Dualshock 3 Controller etc.) work. I don’t know if the reason why my hdd does not work is that wire. Will test it by monday and upgrade my post.
My own made cable is attached below, not perfect, but good, working fine
Thanks to SebastianFM