A sensing system for a computer keyboard includes a plurality of key sensors, a multiplexing system (Fig.8) and at least one detector to detect a level of radio frequency (RF) signal from a driven key sensor for sensing a position and/or velocity of an associated key. Each key sensor may include an actuator 15 and comprises an active resonant circuit 10 and a passive resonant circuit 11, the active resonant circuit being configured to excite the passive resonant circuit at its resonant frequency. Additionally, at least one sensor driver is provided to drive the active resonant circuit with an RF signal at the resonant frequency. The multiplexing system is configured such that no key is driven at the same time as an adjacent key in each of two dimensions. A backplane 10a for the sensing system is also provided, the backplane bearing a plurality of the active resonant circuits each comprising a coil with one or more windings, wherein at least some of the active resonant circuits are paired and configured to have windings of opposite sense to the other in the pair. The system may be used where reliability and key activation sensitivity adjustment is desirable.
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