Published:2011/6/24 2:46:00 Author:Zoey | Keyword: 555Oscillator circuit, in synchronism with clock | From:SeekIC
The oscillation of the oscillator is determined by the level of pin 4 in the reset terminal. Without RF signal, pin 4is in low level and 555 ceases to oscillate. When specified RF signal is available, the wave is detected by detector diode D1 and the video signal is placed on pin 4. When signal level turns to be higher than 1V, it starts to oscillate, and the speaker will sent out audio signal adjusted.
Figure3-14 Audio oscillator Circuit driven by RF Figure 3-15 Oscillator circuit in synchronism with clock
As shown in the figure 3-14, 555,R1, RP1 and C1 constitute a controllable audio oscillator, and f=1.44/(R1+2RP1)C1, frequency of parameter in the picture is between 600Hz~20kHz, which can be adjusted by RP1.
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