I understand you can create a serial transmission between the Raspberry Pi and an Atmega328 using the GPIO: http://www.raspberrypi.org/phpBB3/viewtopic.php?t=22736&p=293668
I'm interested in having more serial options, like the USB ports. I managed to do so, but with an Arduino board: http://www.doctormonk.com/2012/04/raspberry-pi-and-arduino.html
I've searched a lot on this topic and got pretty confused. Is there a safe way to use the RPi's USB port for serial communications with an Atmega328? What would be the easiest safety intermediate circuit? Thanks!
(Note: Easiest as in minimal number of components, like transistors and resistors. Preferrably NOT ICs. This is to reduce size and ensure availability of components in my country)