| 摘要 |
A standard dual timing integrated circuit contains two independent 555-type timers on a single monolithic chip, each timer section has a terminal pin for connection to external circuitry for supply voltage, control voltage, and has internal circuitry which has terminal pins for connection to external circuitry for reset, trigger, output, discharge, and threshold connections. A multiple resistance-capacitor circuit is connected to the discharge, threshold, trigger, and ground pins of the first timer section with the resistance values being manually selectable between three discrete resistance values, each corresponding to a predetermined sound mode, to provide three separate discharge rates of the capacitor and thus provide at the output pin of the first timer section a voltage waveform of one of three predetermined configurations corresponding to the selected sound mode. Thus, the first timer section acts as a modulator. Wave shaping circuitry comprising a resistance-capacitor circuit having multiple discrete selectable capacitance values which are manually selected with the selection of a sound mode waveform, is coupled between the output terminal of the first modulator timer section and the control terminal of the second timer section. The second timer section is connected as a free running multivibrator and has a speaker connected at its output. Thus, the second timer section is employed as a voltage controlled oscillator with the shaped waveform applied to its control input causing a corresponding frequency at its output and a corresponding audible tone from the speaker.
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