FTDI (Future Technology Devices International Ltd.) is a popular and reputable designer and manufacturer of USB-to-Serial converters. They make a range of IC’s for this purpose, as well and manufacturing useful products which use these IC’s (such as USB-to-serial cables).
As of 2016, their IC’s are commonly found in good quality USB-to-serial hardware (more so than one of their main competitors, Prolific
USB-to-Serial converters introduce a fair bit of delays into serial communications. and depending on your latency requirements, this may effect your design.
The below image is a screenshot of FTDI RX/TX data captured with a logic analyser. The computer was running Java code which sent an 0x02 response as soon as it received an 0x01 byte.
FTDI provides the Java D2xx API for Android systems. The API is packaged into a file called d2xx.jar and can be downloaded from http://www.ftdichip.com/Android.htm.
Basic information on the driver software can be found at http://www.ftdichip.com/Support/Documents/TechnicalNotes/TN_147_Java_D2xx_for_Android.pdf.