MAX3232 RS232 to TTL Serial Port Converter Module Pinout, Features & Specifications
Amazon.com: ANMBEST 2PCS MAX3232 3.3V to 5V DB9 Male RS232 Serial Prot to TTL Converter Module Root Connector for Arduino Raspberry Pi and Microcontrollers : Electronics
Reading RS232 with MAX3232 module - Project Guidance - Arduino Forum