A touch panel or screen has a serpentine transmission line fabricated on a substrate, e.g., printed circuit board, LCD, plasma or LED screen, etc., and has a constant impedance. Touches to the touch panel will cause changes of impedance of the transmission line at the locations of the touches. Time domain reflectometry (TDR) is used for determining the locations of the changes of impedance of the transmission line by accurately measuring the return pulse times at the source of a plurality of pulses, and then converting the return pulse times to X-Y coordinates of the touch panel or screen.