Piezoelectric audible alarm frequency self-calibration system

A system for driving a piezoelectric transducer at an optimum frequency at which maximum output power level results, the optimum frequency known to be within a specified frequency range, said system comprising:

• means for generating a feedback signal representative of transducer output power level;
• a threshold detector responsive to the feedback signal and operable to generate one output signal state when the feedback signal level is below a predetermined threshold level and to generate another output signal state when the feedback signal level is above the predetermined threshold level, the predetermined threshold level selected to be lower than the maximum expected feedback signal level when the transducer is driven at the optimum frequency, and higher than the expected feedback signal level when the transducer is driven at frequencies on either end of the specified frequency range;
• and
• a control device for periodically determining transducer optimum frequency and for driving the transducer at the optimum frequency when output is called for, said control device functional to drive the transducer at at least various frequencies within the specified frequency range for determining a pair of threshold frequency points on respective lower and upper sides of the optimum frequency, the threshold frequency points being recognized by a difference in said threshold detector output state when the transducer is driven at frequencies slightly above and slightly below each threshold frequency point, said control device functional to determine said optimum frequency as a function of said threshold frequency points, and said control device thereafter functional to drive the transducer at said optimum frequency when output is called for.