The Android Phone computer (Part 1) - Can I use a USB Keyboard or Mouse?

5/7/2012 6:07:01 PM

Is it a phone or is it a computer? We make an odd hybrid device from his Android phone

The computing power inside a modern smartphone is amazing, especially if you look at in the context of previous mainframe systems. Cray’s first powerful system was the Cray-1A. it weighed 5.5 metric tons and could achieve 160 MIPS and 250 floating point megaflops for those with the $9m to buy it back in 1977. The ARM Corex-A9 used in many of the latest phones can do 2.5 gigaflops and 8000 Dhrystone MIPS running at 1.5GHz, which is quicker than most of the mainframes that were made in 80s.

Description: The Android Phone computer (Part 1)

Description: ARM Corex-A9

ARM Corex-A9

That’s about the same power that we had in desktop PCs nine years ago, equivalent to an AMD Athlon XP 2500+, or close enough. There are people I’m sure still using their Athlon XP systems as perfectly usable computers, as the mount of power needed to word process and surf the internet isn’t huge.

Description: AMD Athlon XP 2500+

AMD Athlon XP 2500+

With so much power in your pocket, is it possible to turn your smartphone into a useable PC? Maybe. But before we tackle some of the bigger issues, perhaps first we need to address getting information into the phone in a slightly more elegant way than with a tiny touch panel.

Can I use a USB Keyboard or Mouse?

At first glance that seems like an impossible dream, not least because when you plug an Android phone into a PC it acts as a peripheral, where what we want it to do is function as a USB host. Surely, then, that’s not going to work, ever?

Amazing, it will work, but under very particular circumstances. What is implemented on some Android phone USB ports is USB-OTG (On-The-Go), a version of USB where the port can act as both a host and a peripheral.

Description: USB-OTG


To do this you need either a special cable, which I found on eBay for $5, or you can actually butcher some USB parts to make one. I respectfully suggest you pay the nice eBay vendor, because getting the power line connections wrong could fry the port, which would make your phone impossible to directly charge among other issues.

This would all be just an interesting technical point had Google not put in Android (or at least the latest versions of Android) the code needed to make a USB keyboard and mouse work. It also put other interesting code in there too, which makes external storage, like USB keys and external hard drives work. The only caveat is that external drives need their own PSU, because the phone won’t provide enough power to drive them directly.

But before you all rush off to buy a cable, I’d do some research first, because while the hardware in my HTC does support OTG, that company, in its less than infinite wisdom, chose not to bind the code that makes it work into the kernel.

So what are the limitations of this if it does work for you? Well, the first issue you’ll encounter is that you’ve only got room for one device, but you can’t get around this with a USB hub. A powered hub is ideal, and using it you can connect a mouse and keyboard easily.

‘With so much power in your pocket, is it possible to turn your smartphone into a useable PC?’

I tried a keyboard with integrated hub on a OTG enabled phone and it complained it was a ‘high power USB device’, so it’s critical to have a powered hub for some devices.

You can also attach flash drives and USB hard drives, as long as they don’t pull too much power. Most Android phones understand the FAT32 file system, but only a few custom ROMs have been augmented to understand NTFS so far.

Unfortunately, the phone I was focusing most of my effort on, the HTC Sensation XE, appears to have not had this feature enabled, although the Samsung Galaxy S2 that I also used worked flawlessly with lots of USB devices.

A side note to this feature is that my research suggests that almost all Samsung Android phones have working OTG, as do most of Nokia’s better Symbian ones, but at this time I can’t find a single Microsoft WM7 phone that has it. As for tablets, for those that don’t have normal USB connectors, the Acer Iconia Tab A200, Sony Tablet S 3G, Samsung Galaxy Tab and Huawei MediaPad S7-301w all support OTG.

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