I have two of those clean robots from iRobot ... and just for fun i dicided to build my own virtual-wall clone .. well they are quite cheap on ebay so there's no real reason for that except hobby ;-)Print it and attach your electronics to it.a sample circuit is attached ... it can produce any signal you like ... also some sample code .. producing Roomba signals ... the code is from "http://adrianlombard.wordpress.com/2009/01/18/arduino-irobot-infrared-communication/" .. i just changed a few things ...please note: if you use a attiny85 .. you have to "burn the Bootloader" in the arduino-ide to get it running at 8 mhz ... by default it is running at 1 mhz ... well a arduino is running at 16mhz so you have to divide all timings by 2 ... thats the reason why: const int PULSE_WIDTH = 5; // time between pulses, in microseconds is 5µs instead of 10µs ... so everything is said .. except .. the MC7805CT supports input-voltages from 5v to 18v ... i use a 9v-block battery to powerup the virtual-wall.!!! UPDATE !!! -= Please not a build another one .. and that wasn't running ... i triggered out that the 330 Ohm resistor is to low for the IR-Diode and the Current will block the ATTiny ... just us a higher Resistor ... at the moment i use 2*330R .. =- !!! UPDATE !!!