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Astable Multivibrators/Oscillators

  1. Jan 20, 2009 #1
    I have a very confusing teacher for my electronics lab, I am suppose to design an astable multivibrator with an output frequency of 5KHz and a duty cycle of 70% using a 555 timer.

    Thats what I'm suppose to do in lab I have the following pre-lab questions that I can't find information for....

    What is the period of the output signal? Give your answer in microseconds.

    I have this formula T= 0.693 [(Ra+2Rb)C1] am I suppose to use the following frequency formula to find the values of Ra, Rb and C1. f0=1.44/(Ra+2Rb)C1 if so I don't understand.

    The other questions have to deal with how long should the high be for each cycle and how long with the low be for each cycle, I can't even find a formula for that in my textbook.

    Any help would help. Thanks
  2. jcsd
  3. Jan 20, 2009 #2
    What is the relationship between frequency and period. If you know the frequency is 5 kHz, what is its period?

    Take a look at the link below, particularly page 4 - Astable Operation and page 8, Figure 9d Astable Timing. There are some inconsequential errors in the drawing. Rb is drawn as a short, it should be a resistor. t1 (OUTPUT HIGH) has an extra parent on the left side of Rb. Nevertheless, these formulas should give you everything you need.

  4. Jan 20, 2009 #3
    f= 1/T I knew that part just figured to write the entire question,

    i figure out that Ra= 100 and Rb= 94 and C1= 1 uf

    so should I use the following formula for the high and low

    high = 0.67 (Ra*C)
    low = 0.67 (Rb*C)
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