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Need help with a special type of signal converter

  1. Oct 14, 2011 #1
    I have a project where I'm trying to take a variable frequency input signal and converting it to a fixed frequency, variable duty cycle output signal. The input signal is a sin wave ranging from roughly 150Hz to 6kHz. The output signal needs to be fixed at 150Hz with a duty cycle range of roughly 3-80%. There are several catches though.

    The ratio between the input and output signals is not fixed. There are times where I will need the output signal to be a specific duty cycle. For example, when the devise is first turned on, I need the output signal to be at ~25% for about 3 seconds without an input signal. If after the 3 seconds there is still no input signal, I need the output to be 75% duty cycle.

    Another example is that I need there to be a user-configured minimum duty cycle output. So regardless how low the input frequency gets, a user needs to be able to set a minimum duty cycle of 10%, 20%, etc.

    At the same time, there needs to be a user-configured setting of when duty cycle reaches 50%. When there is an input signal, maximum duty cycle needs to be 50%. A user needs to be able to adjust when 50% is reached in the input frequency range.

    Because of the complexity, I was leaning towards a programmable devise like a Parallax BASIC stamp. That way, I can program the logic that I need.

    Developing this type of devise is a little bit beyond my capabilities at this time. I'm hoping that some people here can give me some ideas on how to proceed. Thanks!
  2. jcsd
  3. Oct 14, 2011 #2

    jim hardy

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    Science Advisor
    Gold Member


    so you need a 150 hz pulse train
    with adjustable pulse width

    a one shot triggered 150 times per second would set your minimum width, and 10% would be 2/3 msec;
    followed by a "pulse stretcher" - 'OR' it with one of several other one shots set to whatever duty cycle you want. One of them would be variable, and one of them an "input present" detector (known in the trade as 'dead man timer' or 'frustrated one-shot'.

    first task is to make yourself a table of duty cycle vs microseconds.

    whether this runs on 555 timers or a "stamp" is immaterial at this point
    you need to make a block diagram. Then either wire it up or write a Basic program that does the same thing.

    have fun!

    old jim
  4. Oct 19, 2011 #3
    Here is a bit more info on what I'm looking for.


    So here is what I'm looking for as far as output duty cycle with relation to frequency when there is an input signal. Without an input signal, the output needs to be 75% aside from the 3 seconds of 25%.


    I'm leaning towards a stamp because I do have programming experience in several programming languages. However, I have no experience with 555 timers. If this can be done with 555 timers, I'm all for it. I would just need some help.
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