PWM is used for things like controlling servos, motors and LEDs. Output from a micro-controller is easy, and the hardware usually handles it. Remote control receivers also output it, as they are used to control these things as well. RC transmitters often output the closely related PPM (aka CPPM). It's not unusual to want to read those values with an Arduino microcontroller, but this is not as easy, as common - meaning ATmega328 and similar - hardware doesn't do it directly. So let's look at some options to do that.