What kind of touch panel are you using, capacitive or resistive?
You can have a low cost resistive touch panel from the market, with 4 wires. Connect two wires two two ADC channels, say Xout and Yout, and give 5v to other two wires say Xin and Yin when required.
Design you program based on the following logic,
1) Give 5v to Xin
2) Read Xout which is the voltage equivalent to the X-cordinate of a touch
3) Give 5v to Yin
4) Read Yout which is the voltage equivalent to the Y-cordinate of a touch
5) Go to step 1