A simple COM to USB bridge for STM32F4
This app have same functionality with FT232 device. It's just to fast setup a link with computer in case if you don't have FT232.
Based on http://we.easyelectronics.ru/STM32/stm32-organizaciya-virtualnogo-com-porta.html and http://we.easyelectronics.ru/STM32/primery-raboty-s-usb-device-dlya-stm32f4-discovey.html