A user input device is disclosed adapting the electronic components of a time-domain reflectometry material level sensor to replace traditional user input devices such as push-buttons, control knobs, and variable sliders. An electrical conductor is arrayed beneath an input panel, such that when a high permittivity or high conductivity material is placed in proximity to the conductor, the characteristic impedance of the conductor is altered at that point, reflecting electronic pulses transmitted through the conductor. The reflected electronic pulse is received by the associated electronics, and the position of the material along the conductor subsequently determined. By segmenting the conductor into virtual regions, each corresponding to an individual "button", discrete input may be received by the device based upon the placement of the material within specific virtual regions. Alternatively, the conductor may function as an infinitely variable "slider" control, with movement of the material along the conductor producing a proportionally varying output signal.