why chicken to use 12V AC? it's very small voltage only. use 1N4001 diode to convert it to dc, u get the voltage u want. or if not, take a transformer, step down from 240 to 12V. u can externally control the dc motor. power the motor using other circuits but control the circuit using parallel port or serial port. i don't have time to draw it for you only cause i am busy doing my final year project. if not i will draw it for you. don't be chicken. 12V AC is very small only. I have seen 22kV voltage power also. step down to 415V to power up a AC motor ( high tension motor). the load almost 18tan inside.(ball mill, grind silica or sand) the starting load current is 4000A plus. this fry parts of the substation. (fire) then, they changed a few stuff and directly bypass the protection circuit. still can work but no protection on the substation only.(testing only) they did not include the fluid coupling in the design. (bought second hand machines from australia) if they include the fluid coupling, all will be well for that machine. 12V at most fry some of the components only.
seems that this is a very good site for people. decided to be active in it once i finish my degree.