keypads giving numerical outputs

Hi
I'm making a unit convert that can convert between gallons, litres and pounds of fuel to be put into aircraft and give a numerical output on a display.

My idea is to use a keypad to give an input to a PIC chip which can then do the maths and send this to LCD firmware to get an output.

Does anyone know of an IC that I can get to send a pulsed or binary number, that may be upto 4 decimal digits long, into the PIC, from the keypad. Or indeed any other way of doing this. I am on a very thight budget so please don't suggest linking it upto a laptop :lol:

I can get any PIC upto a 40 pinner with twenty something i/o pins, although I would like to use ther smallest chip possible.

Please help me :wink:

The PIC can easily do it all, check my tutorials, particularly the keypad ones!.