For which type of serial communication is Arduino Severino designed? Arduino has become quite costly where I come from (2/3 of the price of Raspberry PI) so I have created an Arduino Severino clone.

I had used the device with the RS-232 Usb-Serial converter. But after a (long) while, the device stopped working. My friend came up with a point that RS-232 communication ranges between +6 to -6 V (with thresholds at +3 and -3 volts).  

So I have tried FT232 which uses 0 to 5 volts instead. I have a little Chinese FTDI chip designed to do that:




However, after connecting it, it behaves unexpectedly. (it had crashed my PC, one of the communication LEDs is on all the time...) I realised that the Arduino board might get broken for a different reason (an accidental short-circuit is very likely).

So for which type of communication is this "Arduino" designed?
Looking at the schematic of that board it uses a very crude signal inversion for the RS-232.  This allows it to work of a standard RS-232 signal direct from a computer - just.

It's far from ideal and really should use a MAX232 (or similar) chip for the interface.

Your FT232 adaptor should bypass that chunk of the circuit and connect direct to pins 0 and 1 of the Arduino clone.  The DTR pin of the FT232 should connect to the RESET pin of the Arduino clone via a 100nF capacitor to allow the IDE to reset the board to enter the bootloader.  Oh, and of course, connect the ground to your Arduino clone too (something Arduino users often forget).

You can follow the serial breakout board portion of the Arduino breadboard tutorial and apply it to your board.