| 摘要 |
An audible indicator circuit including a piezoelectric crystal and transistor device, that is of extremely simple and inexpensive construction and has its on-off operation selectively controlled in response to an automatic or manually applied control signal. The piezoelectric crystal is connected between the collector and emitter electrodes of the transistor, so that with an "on" control signal applied to the base electrode and a supply voltage of magnitude that exceeds the collector to emitter breakdown voltage coupled to the collector electrode, the circuit is caused to oscillate and thereby emit an audible signal.
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