SparkFun XBee Explorer Dongle (SparkFun WRL-11697) FT231X USB-to-Serial converter
USB to RS232 cable with FT231X Chipset — Connective Peripherals - Global Store
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SparkFun FT231X Breakout Kit - Complete with Full UART Hardware Handshake Feature - Compatible with Arduino or General Serial Applications Uses DTR Instead of RTS MicroUSB: Amazon.com: Industrial & Scientific
PDF) FT231X Datasheet - USB TO FULL HANDSHAKE UART IC