I have a fully working Arduino code for data acquisition using Arduino Mega internal ADC, displaying data on a 2.4-inch TFT touchscreen shield (parallel mode data communication), and storing data in a micro-SD card when a button is pressed on the touchscreen LCD.
However, for the project requirement, now I need to use the external ADC reference. For this purpose, I have applied a 3.5 V reference signal at the AREF pin and have set the analog reference using the command 'analogReference(EXTERNAL)'. There is no issue with signal acquisition and displaying on the LCD screen. However, touchscreen buttons are simply NOT able to sense touch, even with significant pressure applied.
It would be a great help if someone can point out what could be the issue with using external analog reference in the code and the non-working of the touch feature of the LCD display.
Regarding this problem, I had later observed that the touchscreen calibration is getting affected when an external voltage (<5 V) is applied at the AREF pin. Recalibration of the Touch controller is needed. However, I am not sure why this is happening.