Resistive touchscreen to ADC
You don't need such a complicated circuit. You need 4 ports and possibly two resistors.

There are 4 pins for the touch Screen (Page 12 of the PDF):

Pin1 = Y-

Pin2 = X+

Pin3 = Y+

Pin4 = X-

To get the “X” touch position, the microprocessor sets Pin3 to +3.3V and Pin1 to GND (0V).
Pin4 is made unconnected (high impedance) by setting it to an input or an open collector output set to high. The microprocessor uses Pin2 to read the voltage through the ADC.

To get the “Y” touch position do the opposite. The microprocessor sets Pin2 to +3.3V and Pin4 to GND (0V).
Pin1 is made unconnected (high impedance). The microprocessor uses Pin3 to read the voltage.

Pin2 and Pin3 need to go to ADC, through a resistor if you want the control current down. Pin1 and Pin3 go to an open collector output or a regular I/O.

The resistor used on Pin2 and Pin3 will not really affect the ADC if you put a 100pF cap to ground right beside the microprocessor.

To summarize: 

“X” touch position:

Pin1 = 0V output

Pin2 = ADC input

Pin3 = 3.3V output (with inline resistor if needed)

Pin4 = High impedance (open collector output or just an input)



“Y” touch position:

Pin1 = High impedance (open collector output or just an input)

Pin2 = 3.3V output (with inline resistor if needed)

Pin3 = ADC input

Pin4 = 0V output



Please see the link below if only for the pictures:

https://www.sparkfun.com/datasheets/LCD/HOW%20DOES%20IT%20WORK.pdf