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Homework Help: Frequency question - 555 timer driving a transducer

  1. Oct 8, 2009 #1
    1. For a school project we're building an emergency braking system. In addition, we also want to trigger an audio-visual alarm system to alert a third party to the operation of the system. For the alarm system we are using a 555 timer to generate a squarewave output to alternate a buzzer between on and off [and possibly a light too]. We've placed in 4 JK flip flops to extend mark and space time to give a nice gap between sound and no sound. We've played around in Multisim to achieve this and after calculations we have 62.5 Hertz. Now this is quite low, we'd ideally like a shrill around 1kHz but by doing this mark and space time are too small.

    Is it possible to maintain a high pitch output whilst still achieving a lengthy mark and space time? Or does it not matter what the frequency for your output is, only the voltage, when powering a buzzer?

    Also, we are very confused because we're getting a final output of one complete cycle as around 16 milliseconds, however the buzzer in multisim isn't switching from on to off and then back to on in this time, it's taking much longer. Am I missing something?

    2. The output of the 555 timer is:
    T = time period in seconds (s)
    T = 0.7 × (R1 + 2R2) × C1
    T = 0.7 × (28.86k + (2 x 57.72k)) × 10n
    T = 1.0101 milliseconds
    We then have it going through 4 JK flip flops:
    1.0101 ms x 16 = 16.1616 ms

    The frequency output from the last JK is 62.5 Hz

    Attached Files:

    Last edited: Oct 8, 2009
  2. jcsd
  3. Oct 8, 2009 #2


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    Science Advisor

    Your 555 will be oscillating at about 1000 Hz.

    You could take this to a transducer and get a 1000 Hz tone.
    A transducer is like a speaker and just gives whatever frequency you feed into it.
    A buzzer gives whatever frequency it is designed to give.

    If you wanted to turn the 555 on and off, you could have another 555 operating at about 2 Hz and switching the 1000 Hz one on and off by alternately raising its reset pin to 5 volts or dropping it to zero.
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