Hello, and welcome to the forum.
I have not previously used a touch-pad device, so my comments will be of a general nature. Do you have a specific touch panel part in mind? I assume that you require to emulate a 4 by 4 keypad?
If the end-to-end sheet resistance is about 1k ohm, and assuming 3.3 volt Vdd, this will result in an additional 3 mA current draw. If the wireless device is battery operated, this may be significant if applied for lengthy periods. You would probably need to use a sampling arrangement, with low duty cycle.
The driver circuitry shown in the reference seems to somewhat inconsistent (perhaps there is a drawing error), and is too complex.
It may be feasible to connect the bottom and left-hand electrodes each directly to a MCU pin. Either an output low state, or ADC input mode, would be selected during the operation sequence. A high value pulldown resistor, at each pin, would still be necessary to control the voltage for the "no contact" state.
For the top and right-hand electrodes, simple PNP (or P-channel) transistor drivers will probably still be necessary. This will allow the electrode voltages to "float", when not driven high. Otherwise, a direct MCU connection might require the use of pins with an alternative ADC input mode available, to prevent additional current draw in the internal digital logic circuitry, because of the floating state.
I assume that you would keep your keypad features away from the bottom left-hand corner, to avoid any potential confusion with the no contact voltage levels.
Regards,
Mac
