You could left the rc system on your car and make a controller on your calc, for example 2nd to stop/'launch' car and left/right to drive it...
You just need a part of a calc cable, and maybe a one-bit memory (2 NOR logic circuits for example), and leds if you want.
I can make you program if you want (already done ...).
i thought of that too, but i din't know how to check the bytes in an analog way. in fact, that was my first thought xp
so, how do you do that? well, it would be great to see the program, but i would first like to understand how the splitting works

@ renatose, it has Rx and Tx, so TTL should work Ö
that's not really for sending, but to read from things like temp stuff and so