Why "must" you buy an USB HOST Shield to Talk to an Android Device?

I would think you could use the USB jack that is already on the Arduino Uno Rev. 3 Couldn't you use a USB A Female to USB B Male Adapter that you can pick up for a few pennies. Then plug your cell phone into it the same as you would the USB Host Shield? Just seems like you should be able to make the Jack you already have work versus buying the USB Host Shield. Anyone been down this road that knows why we may need the shield or how you may make this work without it? Thanks for your time and consideration on this topic.

Cybrpro: I would think you could use [/quote] USB connections are not symmetrical. Once side must be a USB host and the other must be a USB slave, and the interaction between them is complex. You can't simply plug two USB slaves into each other and get a working connection. There are Arduinos with an integral USB Host port, and ways to add a USB host to other Arduinos using shields or separate boards, but one way or another you must have a USB Host port in order to connect to a USB slave device. For more details of why this is, use Google to understand how USB works, but be warned that it is a complicated subject.

Thanks for the Infos. Got to love Google! Found this so far sounds interesting may work. http://mcuoneclipse.com/2012/10/15/usb-host-mode-hack-for-the-freedom-kl25z-board/

if your android device supports USB OTG, good for you! just plug in the cable and android will find the CDC.

if your android device doesn't support OTG, then a host shield is required.

Thanks for the Infos.