An electronic learning/teaching device operates with and without a printed
sheet element having an arrangement of selectable content by means of a
user responsive sensor array beneath a surface configured to receive the
element. The sensor array is formed by cross-points of two sets of
crossing conductive lines, one set being driven sequentially with a radio
frequency square wave and the other set being sampled sequentially though
a high impedance amplifier connection with an asynchronous detection
circuit. Where more than one cross-point location is user activated,
algorithms are used to identify one cross-point sensor location as the
user activated selection.