An electronic drive system for a droplet spay generation device of the type having a droplet generator including a perforate membrane driven by a piezoelectric transducer, the electronic drive system comprising: a programmable micro-controller providing a power supply for converting, in use, a battery supply voltage to power the device; a power amplifier connected to receive electric power from the power supply and supply a drive signal to the piezoelectric generator in use; and wherein the micro-controller is also arranged: to control the operation of the power amplifier, including the drive signal operating frequency at substantially its resonant frequency; to measure the current provided to the power amplifier by the power supply at a plurality of different frequencies; to determine, as the resonant frequency of the droplet generator, the frequency at which the maximum power is consumed by the amplifier, and to set the drive signal operating frequency at the resonant frequency.