How to: Make your own USB OTG cable for an Android smartphone

Some high-end Android phones and most of today’s Android tablets support USB OTG (On-The-Go). This enables users to connect standard USB input devices such as keyboards and mice, or even extend storage using a regular USB pen drive. However, only a few Android tablets are equipped with a USB host port (Type A Female connector), while no mobile phone is. Some mobile phone manufacturers ship USB host ports with their handsets while others have them as optional accessories, usually at a premium price.

In order to connect an Android phone to a standard USB device, you need to use a micro (or mini) USB to USB Type A Female convertor, but this should also be an OTG cable. A mini USB OTG cable is available in the market and can cost you around Rs.150 – Rs.300, but finding vendors who actually sell it is not easy. The ones that are available are not guaranteed to work. The case of the micro USB OTG cables is also similar.

USB connector types

In this workshop, we show you how you can build yourself an OTG cable (be it micro or mini) at almost no cost. Do note that the procedure mentioned here will involve hacking into your existing cable, and even a small blunder can potentially damage your cable or the device you use it with. Proceed with extreme caution as we take no responsibility for any damages to your device. Do this at your own risk. Furthermore, do take note of your Android specs and check carefully to see if it has OTG capabilities before trying out this workshop. Phones don’t need to be rooted as the stock ROM usually supports OTG in compatible handsets. Those who have installed third-party developer ROMs should check with the developers if the OTG feature is enabled in the kernel.

Slicing the connector sleeve

Since all phones usually ship with cables, we suggest you opt for a second one from the market to create the OTG cable. For those who are not able to find a similar cable, this workshop will also show you how you can use the same cable for regular and OTG modes. In the following procedure, we'll be using a micro USB cable that we’ll convert to be used with USB OTG.

Requirements:

• A standard mini or micro USB cable
• Some small, thin wires
• A sharp knife
• Soldering iron and solder wire
• Wire cutter
• Hot glue or any quick glue

Firstly, we need to slice open the micro USB connector end very carefully using a knife. The idea here is to cut the outer sleeve (length-wise) into two halves to reveal the connector inside. Be careful not to destroy the outer sleeve as we shall be glueing it back on after the work is done. 

A miniature switch

After the sleeve is taken apart, some of you might find a whitish plastic mould covering the connector’s leads. This is for strengthening the cable to connector contacts, and its use depends from manufacturer to manufacturer. Those who have this mould will also have to cut through it to reveal the connector leads. On revealing the connector leads, you will find that it has five leads and not four. The usual four are power, data, data and ground, while the non-connected lead is sense. This lead needs to be grounded before connecting the cable for the phone to switch to OTG mode and sense a USB device connected to the interface.

The difference - circuit

Given above is the pin-out diagram for the micro and mini USB connector.

Pin 1: VCC

Pin 2: data

Pin 3: data

Pin 4 Not connected / unused

Pin 5: ground

In order to get the phone to go into OTG mode, we need to short Pins 4 and 5. You can either choose to short them permanently by soldering them together or soldering two wires to each of the pins and leading those outwards from the connector, which can then be soldered to a small switch. Using the switch, we can switch the cable between normal and OTG whenever needed. If you choose to short it permanently, you will have to cut off the connector at the other end (The Type A Male USB connector) and solder a Type B Female connector to accommodate a USB device. You can also choose to have a male to female USB convertor at that end. Here's what we did:

The connector and the sleeve

We chose to connect a small switch to the leads at Pin 4 and Pin 5 and glue the switch to the wire itself. This way, we could use the cable for both regular and OTG purposes. Next, we glued the connector sleeves back carefully using hot glue. Now the other end of the cable, which has a male USB connector, needed to be converted into a female. For this, we opted for the scrapped USB rear panel connector of a desktop PC. We soldered the wires of the USB connector to create a USB female-to-female convertor. Once done, we now have an OTG cable ready for use. Just to ensure we do not end up frying our phone, we used a multimeter to double-check any cable shortings during the soldering. Lastly, we connected the OTG cable to our Android (the Sony Ericsson Live with Walkman) and used a USB mouse with it. If your cable worked for you and your phone is compatible with OTG features, you can also connect a USB hub to the OTG cable and use a USB keyboard, mouse and pen drive together on the same Android device.

Micro USB Pin points

By following this workshop you can now conveniently use a pointing device to control your apps and games, use a keyboard to type e-mails and messages or use a pen drive to store or access media or large files. If you are lucky enough to find a micro USB connector and a Type A Female USB connector at an electronics store though, you can make your own OTG cable for under Rs.100.