For experiments in forced linear oscillation, a square wave is integrated to a triangular wave, and that is shaped by a pair of diodes to approximate a sine wave. The response of a galvanometer driven by the shaped wave matches quite closely the response calculated for a pure sinusoidal forcing function over the frequency range of interest here, from 0.5 to 2 times the resonant frequency. One advantage of the circuit is that the student observes the phase lag quite directly.