frequency to voltage converter?

Discussion in 'General Electronics Chat' started by nyx, Apr 24, 2008.

  1. nyx

    Thread Starter New Member

    Apr 24, 2008
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    hi,
    I'm looking for the simplest way of converting the output of an optical microsensor to a voltage. The sensor is used to determine the rotation speed of a small shaft by means of a disc with small slits... it's basically a square-wave output with a 'low' of 600mV and a 'high' of 1.8V... as the shaft rotates faster, the frequency simply increases...

    so what i need is basically a way to convert this change in frequency to a change in voltage...

    if anyone can point me in the right direction i'd appreciate it greatly :)

    thanks!
     
    Zaid Mahmoud likes this.
  2. mik3

    Senior Member

    Feb 4, 2008
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    Is the duty cycle almost 50% ?
     
  3. Wendy

    Moderator

    Mar 24, 2008
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    The humble 555 can do it almost directly. You build a monostable that is capacitively coupled, and trigger it off the frequency after it has been squared up. You design the monostable for a duration just under the shortest period the freq will have. Integrate the output and you have it, super simple.
     
  4. Caveman

    Active Member

    Apr 15, 2008
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    If you are using a microcontroller, the timer inputs work great for this.
     
  5. beenthere

    Retired Moderator

    Apr 20, 2004
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    If you can run down an LM2907 frequency to voltage converter, it should be what you want.
     
  6. guyromb

    Member

    May 5, 2009
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    Hello,

    I am sorry that im responding to an old message but it's connected to this subject.
    I would like to build a freq. to voltage convertor using 555 chip too.
    I built an fm system: transmit 1khz sound + receive it. I can hear the sound using headphones. However, I want to get this signal so i can turn on a Led or something. Moreover, the receiver is a simple radio fm receiver (audio output).

    Thanks
     
  7. Wendy

    Moderator

    Mar 24, 2008
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    This is called hijacking, and is strongly discouraged at this site. Basically the mods would like you to start a new thread, though it is OK to refer to this one.

    A monostable, any monostable, will convert frequency to voltage. First, figure your maximum frequency, then calculate the period of this frequency. Use 90% of this number for the monostable duration. Have you read this?

    555 Monostable

    When I have a bit more time I'll show you were to take it from there, but the idea is to trigger the monostable every clock cycle.
     
  8. guyromb

    Member

    May 5, 2009
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    I am sorry.. my first time here :)
    So should i open a new thread? or it's ok if i will continue write here?
    I don't really understand how to use the 555 to convert frequency to voltage?
    I have a 555 oscillator on my fm transmitter for 1khz. I just need a circuit that can recognize this signal from the reciever: when i transmit this sound i want to get '1'.
    I can use operational amplifier to compare the volatages but first i need to convert the freq. to voltage but i don't really know how to do it (I can't find lm2917).
     
  9. guyromb

    Member

    May 5, 2009
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    Ops.. I think i got the idea. Tell me if I right.
    The 555 in the receiver will produce something that is smaller from 1khz (like 900hz) and it will go to the op. amplifier and it will compare the other freq. from the signal (1khz) ??
     
  10. Wendy

    Moderator

    Mar 24, 2008
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    No, the output of the 555 (or any monostable) will be PWM. A simple RC intigrator will convert this to a DC voltage.
     
  11. guyromb

    Member

    May 5, 2009
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    I have found a circuit but i still don't really understand :)
    I give the 555 frequency of 1khz and it's changing his wave width? How does it helps? what should I do later to convert it to dc voltage?

    o and thanks for your help :)
    [​IMG]
     
  12. bertus

    Administrator

    Apr 5, 2008
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  13. guyromb

    Member

    May 5, 2009
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    1khz :) you can see previous messages on this thread (page1)

    ty
     
  14. Wendy

    Moderator

    Mar 24, 2008
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    Wrong circuit. Did you read the article I recomended? That is a 555 monostable. 555's are very open ended, they can do lots of jobs.

    The circuit you have displayed is an oscillator.

    Since I'm 3rd shift (10PM-7AM) it is my bed time.

    This is an RC intigrator (ie, low pass filter), taken to the nth degree. Feed the output from the monostable into it (say 1 or 2 RC stages) and you have something approximating what you want...

    [​IMG]
     
  15. guyromb

    Member

    May 5, 2009
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    The 1khz come from FM reciever.... (fm transmitter transmit 1khz sound)
    I just want it will turn on a led or something like that when there is a sound of 1khz.
     
  16. guyromb

    Member

    May 5, 2009
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    Thanks Bill.. I will try now to do it. I'm not sure what to do but i will try :)
     
  17. Wendy

    Moderator

    Mar 24, 2008
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    Hehe, you want a bandpass filter, or something very close. Narrow it down (what you want), and you'll get help matching it.

    Do you want to zero in on 1KHz, or are you after a VOX (voice activated switch)? If it is the latter google VOX, you will be amazed.
     
  18. guyromb

    Member

    May 5, 2009
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    :D hmm first i want that the 1khz will work..

    Oh... The monostable circuit on the 555 datasheet is fine ? Beacuse on your circuit you need too many resistors and components :p
     
  19. guyromb

    Member

    May 5, 2009
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  20. Wendy

    Moderator

    Mar 24, 2008
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    Lets see, 3 resistors, 2 capacitors, and a 555. Ever hear of TANSTAFL? Their Ain't No Such Thing As a Free Lunch. A favorite quote from Robert A Heinlien. Don't forget the resistor and capacitor combo on the output. Good luck! :D

    Very nice, but read my article and you find out why it won't work.

    Good night.
     
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