A wind instrument such as a harmonica has a mouthpiece with one or more air channels, an electric power source, and a means for generating an electrical output signal from strain gages exposed to airflow in the channels. First and second strain gages having variable flow-induced resistance are bonded to a flexible substrate and suspended within an air channel, which includes a divider shelf for directing a first airflow to the first strain gage and a second airflow to the second strain gage. Complimentary strain gages are mounted to an opposite side of the substrate for inverse flexure to enable temperature correction for the first and second strain gages. When a user forces air through a channel in a direction biased to one side of the divider shelf a difference signal is generated by the first and second strain gages and detected by comparing their outputs. The difference signal can be used to adjust a variable control signal in applications such as volume control, dimming lights, or bending notes generated by the harmonica.