Amazon.com: nanoUART Serial Port Tool USB to TTL Module Adjustable IO Level Hardware Flow Control Type-C Interface Open Source Schematic (Default Voltage VREF) : Electronics
USB to RS232 TTL level converter « COBHC member
CH340G USB to RS232 TTL module schematic_KS - EasyEDA open source hardware lab
DIY USB to TTL Converter : 6 Steps - Instructables
USB To TTL Pl2303 - Electra
picprojects.net | RS232 Module, DIL (RS232/TTL Level Converter)
RS232 to TTL Modem Implementation Circuit | Download Scientific Diagram