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1 Hz Pulse Frequency Generator with 555

Konusu 'Elektronik Devreler' forumundadır ve guclusat tarafından 28 Mayıs 2014 başlatılmıştır.

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    Katılım:
    14 Haziran 2009
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    Here is a 1Hz pulse/frequency generator using the popular timer IC 555 which is wired as an Astable Multivibrator. The output pulses can be indicated visually by the LED. An Astable Multivibrator, often called a free-running Multivibrator, is a rectangular-wave generating circuit. Unlike the Monostable Multivibrator, this circuit does not require any external trigger to change the state of the output, hence the name free-running. This circuit can be used in applications that require clock pulses.

    Schematic of the 1Hz Pulse Generator Circuit
    555-1Hz-pulse-generator.png

    An Astable Multivibrator can be produced by adding resistors and a capacitor to the basic timer IC 555.The timing during which the output is either high or low is determined by the externally connected two resistors and a capacitor.
    Clock: A clock is simply a square wave i.e. alternate high & low states. Each alternate high-low forms a clock cycle with a specific frequency & duty cycle. Frequency is the number of cycles completed in 1 sec & duty cycle is the ratio of the time period of high state to the time period of the low state.

    [​IMG]
    We can set the 555 to work at the desired frequency by selecting the right combination of resistances & capacitance.
    Frequency = 1.44 / {(R1 + 2R2) * C1}
    Also, 555 can produce waves with duty cycle else than the 50 % cycle.
    Duty Cycle = (R1 + R2) * 100/ (R1 + 2R2)
    where duty cycle = Ratio of time period when the output is 1 to the time period when the output is 0.

    [​IMG]

    Circuit Working
    Capacitor C1 begins charging toward VCC through resistances R1 and R2 (VR). Because of this, the charging time constant is (R1 + R2( VR)) C. Eventually, the threshold voltage exceeds +2/3 VCC, the comparator 1 has a high output and triggers the flip-flop so that its Q is high and the timer output is low. With Q high, the discharge transistor saturates and pin 7 grounds so that the capacitor C1 discharges through resistance R2 (VR) with a discharging time constant R2 C.
    With the discharging of capacitor, trigger voltage at inverting input of comparator 2 decreases. When it drops below 1/3VCC, the output of comparator 2 goes high and this reset the flip-flop so that the timer output is high. This proves the auto-transition in output from low to high and then to low. Thus the cycle repeats.

     
    Son düzenleme: 6 Mayıs 2016

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