I made this circuit, because i faced several problems with the touch-pad for my keycode doorlock project. I tried many different touch-pad designs, yet all had problems. Designing a touch-pad is not a simple thing after all. There are several considerations to take into account, and as i found out (the hard way) experience is mostly needed. So, here is one touch-pad that works and you can use it as-is for your designs.
10 Buttons PIC Touch-Pad with BCD Output - [Link]
The MC33794-based E-Field Serial Touch Pad is designed around the MC68HC908JK3 microcontroller. The touch pad connects through a PC’s serial port using the same protocol used by serial mice. Commands are performed by moving your fingertip around the system’s pads, which are aluminum. Clicking is performed by gently tapping the middle pad.
E-Field Serial Touch Pad - [Link]