Driving power for a vibrating device is provided at less than full level when the device is initially used. Power is gradually increased in successive steps after a selected number of uses in each step until full power is achieved. Also, a battery-energized driving signal for a vibrating device has a selected characteristic, such as duty cycle, which in set initially at less than an optimum value, when the battery is at full strength. As the battery discharges, the selected characteristic is adjusted toward optimum so as to compensate for reduction in the battery voltage and ensure full power output.
