i want to hook my Uno to the RS 232 output of a vending machine. on wikipedia i read that output levels of RS 232 are typically +-5V, 10V and 15V. The maximum input of Arduino is 5.5V so i probably need to lower this voltage.
How do i do this?
Not only do you need to fix the voltage mismatch between RS-232 signals and an Arduino's TTL voltage levels you also need the signals inverted logically. The best method is to use a module or a circuit based on a RS-232 to TTL converter chip like a MAX232 or other such chips. Also many vendors sell modules to perform the same conversion, like these from SparkFun:https://www.sparkfun.com/products/449https://www.sparkfun.com/products/133