METHOD FOR TESTING A PIEZOELECTRIC SOUND TRANSDUCER

Abstract

A method for testing a drug delivery device comprising a piezoelectric transducer, a microcontroller, and a DC power supply, the method describes the method for having the piezoelectric transducer in an operational and an inoperative state. The method includes providing a drive signal to the piezoelectric transducer of the drug delivery device, determining a drive voltage or drive current value, and comparing the drive voltage or drive current value to a baseline value to determine whether the piezoelectric transducer is in the operational or inoperative state.

Description

METHOD FOR TESTING A PIEZOELECTRIC SOUND TRANSDUCER CROSS REFERENCE WITH RELATED APPLICATION This application claims priority over U.S. Provisional Application No. 63 / 114,879, filed on November 17, 2020, entitled Method for Testing Piezoelectric Sound Transducer, which is hereby incorporated by reference in its entirety. BACKGROUND OF THE INVENTION Field of invention This disclosure relates to a method for testing a piezoelectric sound transducer for a drug delivery device. Description of related technique Personal medical devices, such as auto-injectors, offer the benefit of providing therapy to patients remotely from a clinical facility and / or while worn discreetly under the patient's clothing. The personal medical device can be applied to the patient's skin and configured to automatically administer a dose of a pharmaceutical composition within a predetermined timeframe after application, such as after a 27-hour delay. After the device administers the pharmaceutical composition, the patient can remove and subsequently dispose of the device. Personal medical devices (PMDs) may have audible, tactile, or visual indicators to signal a device status, such as when drug administration begins or is completed, or if a malfunction is detected. Piezoelectric transducers are used to provide audible and / or tactile indicators for PMDs. Because PMD indicators play a crucial role in the device's function, their functionality is tested during manufacturing. One solution for testing audible indicators is to use a microphone, which has limitations depending on the ambient noise levels in the manufacturing or testing environment. BRIEF DESCRIPTION OF THE INVENTION In one aspect or embodiment, a method for testing a drug delivery device that includes a piezoelectric transducer, a microcontroller, and a DC power supply, the piezoelectric transducer having an operating state and an inoperative state, includes: providing a drive signal to the piezoelectric transducer of the ML / a / ZUZO / UUbOUÜ drug delivery device; determine a drive voltage value or a drive current value; and compare the drive voltage value or drive current value with a baseline value to determine whether the piezoelectric transducer is in the operating or inoperative state. The drive voltage or drive current value can be determined from an average of multiple values ​​measured over a predetermined time period. The drive voltage or drive current value can be determined from a subset of multiple values ​​measured over a predetermined time period. A curve fit can be used to determine the drive voltage or drive current value. At least one Fourier transform and one fast Fourier transform can be used to determine the drive voltage or drive current value. A signal used to determine the drive voltage or drive current value can be calculated over a period longer than 10 ms.A signal used to determine the drive voltage value or drive current value can be calculated for a time longer than 1 ms. The drive voltage value can be a DC power supply voltage frequency when the drive signal is applied to the piezoelectric transducer, and the baseline value can be a known DC power supply voltage frequency when the drive signal is applied to the piezoelectric transducer and the piezoelectric transducer is in the operating state. Alternatively, the drive voltage value can be a frequency of maximum voltage drop values ​​when the drive signal is applied to the piezoelectric transducer, and the baseline value can be a known frequency of maximum voltage drop values ​​when the drive signal is applied to the piezoelectric transducer and the piezoelectric transducer is in the operating state. The drive voltage value can be a minimum and maximum voltage of the DC power supply when the drive signal is provided to the piezoelectric transducer, and the baseline value can be a known minimum and maximum voltage when the drive signal is provided to the piezoelectric transducer and the piezoelectric transducer is in the operating state. The piezoelectric transducer can be determined to be in the operating state when the drive voltage value is within a predetermined range of the base line value. The piezoelectric transducer may be actuated in the operating state and not actuated in the inoperative state. Determining the drive voltage value may involve measuring the voltage at the DC power supply terminals or the voltage at the piezoelectric transducer terminals. The DC power supply may be a battery. In a further aspect or embodiment, a computer-implemented method for testing a drug delivery device comprising a piezoelectric transducer, a microcontroller, and a DC power supply, the piezoelectric transducer having an operating state and an inoperative state, includes: providing a drive signal to the piezoelectric transducer of the drug delivery device; determining a drive voltage value or drive current value; and determining with at least one processor whether the piezoelectric transducer is in the operating state or the inoperative state by comparing the drive voltage value with a baseline voltage value. In a further aspect or embodiment, a drug delivery device includes: a DC power supply; a cannula; a reservoir configured to receive a fluid; a pump configured to deliver a fluid from the reservoir to the cannula; a piezoelectric transducer having an operating state where the piezoelectric transducer produces an audible sound and an inoperative state where the piezoelectric transducer does not produce an audible sound; and a microcontroller including at least one processor programmed or configured to: provide a drive signal to the piezoelectric transducer; determine a drive voltage value; and determine with the at least one processor whether the piezoelectric transducer is in the operating or inoperative state by comparing the drive voltage or drive current value with a baseline value. In a further aspect or embodiment, a computer program product for testing a drug delivery device comprising a piezoelectric transducer, a microcontroller, and a DC power supply, the piezoelectric transducer having an operating state and an inoperative state, and the computer program product including at least one non-transient computer-readable medium that includes program instructions that, when executed by the microcontroller, cause the microcontroller to: provide a drive signal to the piezoelectric transducer; determine a drive voltage value or a drive current value; and determine whether the piezoelectric transducer is in the operating state or the inoperative state by comparing the drive voltage value or drive current value with a baseline value. iviA / a / zuzó / uuoouo BRIEF DESCRIPTION OF THE DRAWINGS The features and advantages mentioned above and others in this disclosure, and the manner of achieving them, will become more evident and the disclosure itself will be better understood by reference to the following descriptions of implementations of the disclosure taken in conjunction with the accompanying drawings. Figure 1 is a perspective view of a drug delivery device according to an aspect or embodiment of the present application. Figure 2 is a perspective view of the drug delivery device in Figure 1, with a top cover removed. Figure 3 is a partial perspective view of the drug delivery device in Figure 1. Figure 4 is a schematic view of the drug delivery device in Figure 1. Figure 5 is a schematic view of a piezoelectric transducer circuit of the drug delivery device of Figure 1 according to an aspect or embodiment of the present application. Figure 6A shows a voltage versus time graph of a power supply and piezoelectric transducer of the drug delivery device in Figure 1 when the drug delivery device is powered on and a piezoelectric transducer circuit is inactive. Figure 6B is a histogram of the graph in Figure 6A. Figure 7A is a voltage versus time graph of a power supply and piezoelectric transducer of the drug delivery device in Figure 1 when the drug delivery device is turned on, a piezoelectric transducer circuit is turned on, and a piezoelectric transducer is turned off. Figure 7B is a histogram of the graph in Figure 7A. Figure 8A is a voltage versus time graph of a power supply and piezoelectric transducer of the drug delivery device in Figure 1 when the drug delivery device is activated, a piezoelectric transducer circuit is activated, and a piezoelectric transducer is connected. Figure 8B is a histogram of the graph in Figure 8A. Figure 9 is a voltage versus time graph of a power supply for the drug delivery device in Figure 1, showing a voltage with a piezoelectric transducer connected and a voltage without a piezoelectric transducer connected. ML / a / ZUZd / UUOOUÜ Figure 10 is a voltage versus time graph of a drug delivery device power supply from Figure 1, showing a frequency of peak voltage drops. Figure 11 is a voltage versus time graph of a power supply for the drug delivery device in Figure 1, showing a comparison of a voltage with a piezoelectric transducer connected and a voltage without a piezoelectric transducer connected. Figure 12 is a voltage versus time graph of a power supply for the drug delivery device in Figure 1, showing a comparison of a power supply voltage frequency with a connected piezoelectric transducer and a piezoelectric transducer frequency of 250 Hz. Figure 13 is a voltage versus time graph of a power supply for the drug delivery device in Figure 1, showing a comparison of a power supply voltage frequency with a connected piezoelectric transducer and a piezoelectric transducer frequency of 500 Hz. Figure 14 is a voltage versus time graph of a power supply for the drug delivery device in Figure 1, showing a comparison of a power supply voltage frequency with a connected piezoelectric transducer and a piezoelectric transducer frequency of 750 Hz. Figure 15 is a schematic view of a method for testing a drug delivery device according to an aspect or embodiment of the present application. Figure 16 is a graph of voltage versus number of samples of a power supply for the drug delivery device in Figure 1, showing a voltage with a piezoelectric transducer connected. Figure 17 is a graph of voltage versus number of samples of a power supply for the drug delivery device in Figure 1, showing a voltage without a piezoelectric transducer connected. Corresponding reference characters indicate corresponding parts throughout the various views. The examples set forth herein illustrate illustrative realizations of the disclosure, and such examples should not be construed as limiting the scope of the disclosure in any way. iviA / a / zuzó / uuoouo DETAILED DESCRIPTION OF THE INVENTION Spatial or directional terms, such as left, right, inside, outside, up, down, and the like, should not be considered limiting since the invention can assume various alternative orientations. All numbers used in the specification and claims shall be understood to be modified in all cases by the term approximately. Approximately means a range of plus or minus ten percent of the stated value. As used in the specification and claims, the singular forms of a, one, an, and the include plural referents unless the context clearly dictates otherwise. The terms first, second, and the like are not intended to refer to any particular order or chronology, but instead refer to different conditions, properties, or elements. At least means greater than or equal to. As used in this document, "at least one of" is synonymous with "one or more of." For example, the phrase "at least one of A, B, and C" means any one of A, B, or C, or any combination of any two or more of A, B, or C. For example, "at least one of A, B, and C" includes one or more of A alone; or one or more of B alone; or one or more of C alone; or one or more of A and one or more of B; or one or more of A and one or more of C; or one or more of B and one or more of C; or one or more of all of A, B, and C. As used in this document, the term processor can refer to one or more electronic devices configured to process data. A processor may, in some examples, include the components necessary to receive, process, and output data, such as a processor, a display, memory, an input device, a network interface, and / or the like. A processor can be a mobile device. A processor can also be a desktop computer or another form of non-mobile computer. With reference to Figures 1-4, a drug delivery device 10 includes a reservoir 12, a power source 14, an insertion mechanism 16, control electronics 18, a cover 20, and a base 22. In one aspect or embodiment, the drug delivery device 10 is a personal-use auto-injector, such as an insulin or bone marrow stimulant delivery device. The drug delivery device 10 can be mounted on a patient's skin and activated to inject a pharmaceutical composition from the reservoir 12 into the patient. The drug delivery device 10 can be pre-filled with the pharmaceutical composition, or it can be filled with the pharmaceutical composition by the patient or a healthcare professional prior to use. The Drug Delivery Device 10 is configured to deliver a dose of a pharmaceutical composition, for example, any desired medication, into the patient's body via subcutaneous injection at a slow, controlled injection rate. Example administration times achieved by the Drug Delivery Device 10 can range from approximately 5 minutes to approximately 60 minutes, but are not limited to this range. Example volumes of the pharmaceutical composition delivered by the Drug Delivery Device 10 can range from approximately 0.1 milliliters to approximately 10 milliliters, but are not limited to this range. The volume of the pharmaceutical composition delivered to the patient can be adjusted. With reference again to Figures 1-4, in one aspect or embodiment, the power source 14 is a DC power supply that includes one or more batteries. The control electronics 18 include a microcontroller 24, sensing electronics 26, a pump and valve controller 28, sensing electronics 30, and deployment electronics 32, which control the actuation of the drug delivery device 10. The drug delivery device 10 includes a fluid subsystem comprising the reservoir 12, a volume sensor 34 for the reservoir 12, a reservoir fill port 36, and a metering subsystem 38 comprising a pump and valve actuator 40 and a pump and valve mechanism 42. The fluid subsystem may further include an occlusion sensor 44, a deployment actuator 46, and a cannula 48 for insertion into a patient's skin.In one aspect or embodiment, the insertion mechanism 16 is configured to move the cannula 48 from a retracted position fully inside the drug delivery device 10 to an extended position where the cannula 48 extends outside the drug delivery device 10. The drug delivery device 10 may operate in the same manner as discussed in U.S. Patent No. 10,449,292 to Pizzochero et al. With reference to Figures 3 and 5, the drug delivery device 10 also includes a piezoelectric transducer 50 configured to provide an audible and / or tactile indication to a user regarding the status of the drug delivery device 10. In one aspect or embodiment, the piezoelectric transducer 50 is connected to the control electronics 18 via one or more spring contacts 60. The piezoelectric transducer 50 has an operational state where it is actuated, producing an audible sound, movement, and / or vibration, and an inoperative state where it is not actuated, producing no audible sound, movement, and / or vibration when a signal is supplied from the signal generation system, such as the microcontroller 24. With reference to Figures 6A-15, according to one aspect or embodiment of this application, a method for testing the drug delivery device includes: providing an actuation signal to the piezoelectric transducer of the drug delivery device; measuring an actuation voltage value; and comparing the actuation voltage value to a baseline value to determine whether the piezoelectric transducer is in the operating or inoperative state. If the actuation voltage value is within a predetermined range of the baseline value, such as within 5% of the baseline value, the piezoelectric transducer is determined to be in the operating state and has a test pass status.If the drive voltage value is not within a predetermined range of the baseline value, such as within 5% of the baseline value, the piezoelectric transducer 50 is determined to be in the inoperative state and has a failed test status 80. One possible cause of a failed test is insufficient contact between the spring contacts 60 of the piezoelectric transducer 50 and the control electronics 18. The method in this application allows for self-testing of the drug delivery device 10 to determine whether the piezoelectric transducer 50 is properly connected and operating without requiring dedicated circuitry or hardware and without requiring separate data handling, data processing, and traceability. Method 70 in this application requires no additional equipment and is insensitive to ambient noise.Furthermore, Method 70 of this application, as detailed below, uses a voltage reading from the power supply 14, which is typically already monitored by the microcontroller 24 to detect the power supply levels 14. Therefore, Method 70 of this application does not require an additional connection between electronic components. With reference to Figures 6A-14, in one aspect or embodiment, the drive voltage value is a frequency of the DC power supply 14 voltage when the drive signal is supplied to the piezoelectric transducer 50, and the baseline value is a known frequency of the DC power supply 14 voltage when the drive signal is supplied to the piezoelectric transducer 50 and the piezoelectric transducer 50 is in the operating state. More specifically, the drive voltage value is a frequency of maximum voltage drop values ​​when the drive signal is supplied to the piezoelectric transducer 50, and the baseline value is a known frequency of maximum voltage drop values ​​when the drive signal is supplied to the piezoelectric transducer 50 and the piezoelectric transducer 50 is in the operating state.In one embodiment, the drive signal is a square wave at a predetermined frequency. In a further embodiment, the drive voltage value is the minimum and maximum voltage of the DC power supply when the drive signal is applied to the piezoelectric transducer, and the baseline value is a known minimum and maximum voltage when the drive signal is applied to the piezoelectric transducer and the transducer is in its operating state. In a further embodiment, an operating frequency can be modulated onto a second, lower frequency, essentially by turning the transducer drive circuit on and off as part of the test procedure. The voltage value can be calculated from the difference between the active and inactive voltages measured at a selected location connected directly or indirectly to the piezoelectric transducer.The reference and measured values ​​can be a voltage or an electric current. As shown in Figures 6A and 6B, with the drug delivery device 10 activated or awake and the actuation signal not provided, the power supply voltage 14 measured at the power supply terminals oscillates between 1.505 V and 1.525 V, while the actuation signal remains constant at 1.5 V. As shown in Figures 7A and 7B, with the drug delivery device 10 activated or awake, the actuation signal being provided, and the piezoelectric transducer 50 disconnected, the power supply voltage 14 measured at the power supply terminals oscillates between 1.425 V and 1.455 V, which is an approximate offset of 0.12 V from Figures 6A and 6B, and the actuation signal oscillates between 1.358 V and 1.61 V.As discussed in more detail below, the high-frequency peaks of the maximum voltage drop values ​​occur when the drive signal voltage and the power supply voltage are equal. As shown in Figures 8A and 8B, with the drug delivery device 10 awake, the drive signal being supplied, and the piezoelectric transducer 50 connected, the power supply voltage 14 measured at the power supply terminals ranges from 1.41 V to 1.455 V, and the drive signal ranges from 1.358 V to 1.61 V. Compared to the state in Figures 7A and 7B, the voltage distribution has shifted downward by approximately 5 mV in the state shown in Figures 8A and 8B.Therefore, by comparing the minimum and maximum voltage of the power supply with the known minimum and maximum voltage when the piezoelectric transducer 50 is correctly connected and in its operating state, the operating state of the piezoelectric transducer 50 can be determined. As shown in Figure 8A, the pattern or harmonics of the high-frequency peaks of the maximum voltage drop values ​​are also different compared to the pattern in Figure 7A, which is discussed in further detail below. The pattern can be observed by analyzing the signal in either the time domain or the frequency domain using the Fast Fourier Transform (FFT). With reference to Figure 9, a voltage drop of approximately 0.15 V occurs at the start of the drive signal activation, both with the piezoelectric transducer 50 connected and disconnected. This 0.15 V voltage drop lasts for 0.005 s. As shown in Figure 9, however, the voltage of the power supply 14 recovers to a slightly lower level, a difference of approximately 0.02 V, when the piezoelectric transducer 50 is connected. In a further aspect or embodiment, the drug delivery device 10 test method 70 for determining the operating status of the piezoelectric transducer 50 includes comparing a voltage recovery value after initially providing the drive signal. With reference to Figure 10, an inverted voltage from power supply 14 is shown while the piezoelectric transducer 50 is connected and operating at 2.9 kHz. The frequency of the maximum voltage drop values ​​or peaks of power supply 14 corresponds to the frequency of the drive signal, which occurs only when the piezoelectric transducer 50 is correctly connected. Therefore, by comparing the frequency of the maximum voltage drop values ​​of power supply 14 with the known frequency of the maximum voltage drop values ​​for a given drive signal frequency, the operating status of the piezoelectric transducer 50 can be determined.In other words, if the frequency of the maximum voltage drop values ​​from power supply 14 matches the known frequency of the maximum voltage drop values ​​when the piezoelectric transducer 50 is properly connected, it can be determined that the piezoelectric transducer 50 is in the operational state. If the frequency of the maximum voltage drop values ​​from power supply 14 does not match the known frequency of the maximum voltage drop values ​​when the piezoelectric transducer 50 is properly connected, it can be determined that the piezoelectric transducer 50 is in the inoperative state. If peaks or frequency peaks of maximum voltage drop values ​​are present, but do not match the known values ​​of a properly connected piezoelectric transducer 50, it can also be determined that the drive signal is functioning. iviA / a / zuzó / uuoouo With reference to Figure 11, a comparison is shown of the voltage of the power supply 14 with the provided drive signal and the piezoelectric transducer 50 disconnected and with the piezoelectric transducer 50 connected. As discussed earlier, the maximum voltage drop occurs only at the drive signal frequency when the piezoelectric transducer 50 is properly connected. With reference to Figures 12-14, the maximum voltage drop values ​​are shown with drive signal frequencies of 250 Hz (Figure 12), 500 Hz (Figure 13), and 750 Hz (Figure 14). The maximum voltage drop values ​​occur at the drive signal frequency when the piezoelectric transducer 50 is correctly connected to various drive signal frequencies. In one embodiment, the voltage is measured further from the power source 14 and closer to where power is supplied to the piezoelectric transducer 50. In another embodiment, instead of measuring the drive voltage, a drive current is measured and used to determine whether the piezoelectric transducer 50 is in the operating or inoperative state. The drive current is used in the same way as the drive voltage, as discussed above, to determine whether the piezoelectric transducer 50 is in the operating or inoperative state. The drive current can be calculated by measuring the voltage drop across a resistor, although other suitable arrangements can be used to measure the drive current. With reference to Figures 16 and 17, in one further aspect or embodiment, the method for testing the drug delivery device includes: activating the piezoelectric transducer in an on / off pattern at a rate of 5 Hz for 1 second; recording a battery voltage at the beginning of the second on / off sequence; recording 12 samples of voltage values ​​at a sampling frequency of 120 Hz during 7 on / off periods; calculating and storing an average of the on / off voltage values; using a least squares method to fit a line to all data points during the 7 recorded on / off periods; calculating a perpendicular distance from the 7 average value points to the fitted line; returning a minimum value of the distances; and determining whether the minimum value of the distances is less than 1.5.In one aspect or embodiment, if the minimum distance value is less than 1.5, the piezoelectric transducer 50 is determined to be disconnected. In one aspect or embodiment, if a final recorded voltage value is less than 2 V, the drug delivery device 10 is determined to be faulty. In one aspect or embodiment, instead of recording 12 voltage value samples, two or more voltage value samples are recorded. In one aspect or embodiment, instead of recording voltage values ​​during 7 on / off cycles, voltage values ​​are recorded during two or more on / off cycles. Furthermore, although a sampling frequency of 120 Hz is discussed, other suitable sampling frequencies may be used. Although the invention has been described in detail for illustrative purposes based on what are currently considered the most practical and preferred embodiments, it should be understood that such detail is for that purpose only and that the invention is not limited to the disclosed embodiments, but rather is intended to cover modifications and equivalent arrangements that are within the spirit and scope of the appended claims. For example, it should be understood that the present invention contemplates that, to the extent possible, one or more features of any embodiment may be combined with one or more features of any other embodiment.

Claims

1. A method for testing a drug delivery device comprising a piezoelectric transducer, a microcontroller, and a DC power supply, the piezoelectric transducer having an operating state and an inoperative state, the method comprising: providing a drive signal to the piezoelectric transducer of the drug delivery device; determining a drive voltage value or a drive current value; and comparing the drive voltage value or drive current value with a baseline value to determine whether the piezoelectric transducer is in the operating state or in the inoperative state.

2. The method of claim 1, wherein the drive voltage value or drive current value is determined from an average of a plurality of values ​​measured over a predetermined period of time.

3. The method of claim 1, wherein the drive voltage value or drive current value is determined from a subset of a plurality of values ​​measured over a predetermined period of time.

4. The method of claim 2 or claim 3, wherein a curve fitting is used to determine the drive voltage value or the drive current value.

5. The method of any of claims 2-4, wherein at least one of a Fourier transform and a fast Fourier transform is used to determine the drive voltage value or the drive current value.

6. The method of any of claims 1-5, wherein a signal used to determine the drive voltage value or drive current value is calculated for a time greater than 10 ms.

7. The method of any of claims 1-5, wherein a signal used to determine the drive voltage value or drive current value is calculated for a time greater than 1 ms.

8. The method of claim 1, wherein the drive voltage value comprises a DC power supply voltage frequency when the drive signal is provided to the piezoelectric transducer, and wherein the baseline value comprises a known DC power supply voltage frequency when the drive signal is provided to the piezoelectric transducer and the piezoelectric transducer is in the operating state.

9. The method of claim 1 or claim 8, wherein the drive voltage value comprises a frequency of maximum voltage drop values ​​when the drive signal is supplied to the piezoelectric transducer, and wherein the baseline value comprises a known frequency of maximum voltage drop values ​​when the drive signal is supplied to the piezoelectric transducer and the piezoelectric transducer is in the operating state.

10. The method of any of claims 1, 8, and 9, wherein the drive voltage value comprises a minimum and maximum voltage from the DC power supply when the drive signal is supplied to the piezoelectric transducer, and wherein the baseline value comprises a known minimum and maximum voltage when the drive signal is supplied to the piezoelectric transducer and the piezoelectric transducer is in the operating state.

11. The method of any of claims 1 and 8-10, wherein the piezoelectric transducer is determined to be in the operating state when the drive voltage value is within a predetermined range of the baseline value.

12. The method of any of claims 1 and 8-11, wherein the piezoelectric transducer is actuated in the operating state and not actuated in the inoperative state.

13. The method of any of claims 1 and 8-12, wherein the determination of the drive voltage value comprises measuring voltage at the terminals of the DC power supply.

14. The method of any of claims 1 and 8-13, wherein the DC power supply comprises a battery.

15. A computer-implemented method for testing a drug delivery device comprising a piezoelectric transducer, a microcontroller, and a DC power supply, the piezoelectric transducer having an operating state and an inoperative state, the method comprising: providing a drive signal to the piezoelectric transducer of the drug delivery device; determining a drive voltage value; and determining with at least one processor whether the piezoelectric transducer is in the operating state or the inoperative state by comparing the drive voltage value with a baseline voltage value.

16. The method of claim 15, wherein the drive voltage value comprises a voltage frequency of the DC power supply when the drive signal is provided to the piezoelectric transducer, and wherein the baseline voltage value comprises a known voltage frequency of the DC power supply when the drive signal is provided to the piezoelectric transducer and the piezoelectric transducer is in the operating state.

17. The method of claim 15 or claim 16, wherein the drive voltage value comprises a frequency of maximum voltage drop values ​​when the drive signal is supplied to the piezoelectric transducer, and wherein the baseline voltage value comprises a known frequency of maximum voltage drop values ​​when the drive signal is supplied to the piezoelectric transducer and the piezoelectric transducer is in the operating state.

18. The method of any of claims 15-17, wherein the drive voltage value comprises a minimum and maximum voltage from the DC power supply when the drive signal is supplied to the piezoelectric transducer, and wherein the baseline voltage value comprises a known minimum and maximum voltage when the drive signal is supplied to the piezoelectric transducer and the piezoelectric transducer is in the operating state.

19. A drug delivery device comprising: a DC power supply; a cannula; a reservoir configured to receive a fluid; a pump configured to deliver a fluid from the reservoir to the cannula; a piezoelectric transducer having an operating state where the piezoelectric transducer produces an audible sound and an inoperative state where the piezoelectric transducer does not produce an audible sound; and a microcontroller comprising at least one processor configured to: provide a drive signal to the piezoelectric transducer; determine a drive voltage value or a drive current value; and determine with the at least one processor whether the piezoelectric transducer is in the operating or inoperative state by comparing the drive voltage value or the drive current value with a baseline value.

20. The device of claim 19, wherein the drive voltage value comprises a DC power supply voltage frequency when the drive signal is supplied to the piezoelectric transducer, and wherein the baseline value comprises a known DC power supply voltage frequency when the drive signal is supplied to the piezoelectric transducer and the piezoelectric transducer is in the operating state.

21. The device of claim 19 or claim 20, wherein the drive voltage value comprises a frequency of maximum voltage drop values ​​when the drive signal is supplied to the piezoelectric transducer, and wherein the baseline value comprises a known frequency of maximum voltage drop values ​​when the drive signal is supplied to the piezoelectric transducer and the piezoelectric transducer is in the operating state.

22. The device of any of claims 19-21, wherein the drive voltage value comprises a minimum and maximum voltage from the DC power supply when the drive signal is supplied to the piezoelectric transducer, and wherein the baseline voltage value comprises a known minimum and maximum voltage when the drive signal is supplied to the piezoelectric transducer and the piezoelectric transducer is in the operating state.

23. A drug delivery device comprising a piezoelectric transducer, a microcontroller, and a DC power supply, the piezoelectric transducer having an operating state and an inoperative state, at least one non-transient, computer-readable means including a microcontroller configured to: provide a drive signal to the piezoelectric transducer; determine a drive voltage value or a drive current value; and determine whether the piezoelectric transducer is in the operating or inoperative state by comparing the drive voltage value or drive current value with a baseline value. ML / a / ZUZO / UUOOUÜ 24. The drug delivery device of claim 23, wherein the drive voltage value comprises a DC power supply voltage frequency when the drive signal is provided to the piezoelectric transducer, and wherein the baseline value comprises a known DC power supply voltage frequency when the drive signal is provided to the piezoelectric transducer and the piezoelectric transducer is in the operating state.

25. The drug delivery device of claim 23 or claim 24, wherein the drive voltage value comprises a frequency of maximum voltage drop values ​​when the drive signal is supplied to the piezoelectric transducer, and wherein the baseline value comprises a known frequency of maximum voltage drop values ​​when the drive signal is supplied to the piezoelectric transducer and the piezoelectric transducer is in the operating state.

26. The drug delivery device of any of claims 2325, wherein the drive voltage value comprises a minimum and maximum voltage from the DC power supply when the drive signal is provided to the piezoelectric transducer, and wherein the baseline value comprises a known minimum and maximum voltage when the drive signal is provided to the piezoelectric transducer and the piezoelectric transducer is in the operating state.

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