Pulse divider

Discussion in 'General Electronics Chat' started by spmcgann, Apr 15, 2013.

  1. spmcgann

    Thread Starter New Member

    Apr 15, 2013
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    My current project requires division of a tachometer input from a Hall effect sender. My first attempt was with a 4013 chip and the division by 2 has been successful.

    My next evolution is to divide by 20 using a 4017 and a 4013 (see attached).

    Ultimately, I'd like to also get a divide by 8.8 using the 4017's and dividing by 88 the multiplying by 10 with a 40192.

    All circuits use 12 vdc with 3-18v CMOS chips.

    Also, I'm not an engineer so forgive any blatantly obvious mistakes but please do offer any better designs. I'd like this to be as bulletproof as possible.

    Any suggestions are welcome!
     
  2. WBahn

    Moderator

    Mar 31, 2012
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    How were you planning on multiplying by 10 using a 40192?

    Have you considered using a microcontroller?
     
  3. sheldons

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    Oct 26, 2011
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  4. spmcgann

    Thread Starter New Member

    Apr 15, 2013
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    Last edited: Apr 16, 2013
  5. spmcgann

    Thread Starter New Member

    Apr 15, 2013
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    I was going to use the count up side of the chip.
    I haven't much experience with microcontrollers so I really have no basis for reference. Like I said, I'm open to any ideas.
     
  6. WBahn

    Moderator

    Mar 31, 2012
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    So how is that going to multiply by ten?

    Think it through.
     
  7. spmcgann

    Thread Starter New Member

    Apr 15, 2013
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    Good point.. the BCD output won't really help much
     
  8. spmcgann

    Thread Starter New Member

    Apr 15, 2013
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    I'd like this to be a hardware only solution, plus I'm limited on options that will take up to 15V.
     
  9. WBahn

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    Mar 31, 2012
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    Let's take a step back and be sure that we are on the same page as to what your eventual goal is.

    Correct me where I am wrong, here.

    You have a tachometer that outputs pulses and you want to convert that information to a binary value with the appropriate scaling factor.

    Now, what is this scaling factor? Is it that if the tachometer output is putting out 8.8 pulses per second you want the binary vallue to be 1? If not, what relationship are you looking to achieve?
     
  10. spmcgann

    Thread Starter New Member

    Apr 15, 2013
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    Sorry trying to do too much at once, I have other projects going on at the same time.

    My input signal is 4 pulses /rev @ 2750 RPM (183.3333 Hz). My drive ratio is 5.5:1 so I end up with 22 pulses/rev @ 183.3333Hz.

    If I divide this by 20, (the current circuit design) I get down to 1.1 pulses /rev with a frequency of 9.1666667 Hz. This should give me an output pulse for every 20 inputs.

    I'd like to eventually get around 2.5 pulses /rev (20.833333 Hz) so dividing my original signal by 8.8 gives me that.
     
    Last edited: Apr 16, 2013
  11. WBahn

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    Mar 31, 2012
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    But is the 2.5pulses/rev the goal, or is it an end to a means? In other words, what, at the end of the day, are you interested in? Knowing how fast the thing is turning? Or having a particular pulse rate for some reason? These are two very different things.
     
  12. spmcgann

    Thread Starter New Member

    Apr 15, 2013
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    Ultimate goal is to know how fast it is turning. The frequency at the current pulse rate is too high for the receiver to accurately interpret.

    I've had some success with the 4013 cutting it in half but I'm still not getting the results I'd like and would like to reduce the frequency even more.
     
  13. spmcgann

    Thread Starter New Member

    Apr 15, 2013
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    I see now that the 40192 was the wrong choice.

    I'd like to keep this as a hardware only solution with no programming.
     
  14. WBahn

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    Mar 31, 2012
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    What are the specs on the receiver? What does it expect to see and are there any calibration methods for it? What is the range of speeds on your output that are of interest to you?
     
  15. MrChips

    Moderator

    Oct 2, 2009
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    You could try a binary rate multiplier.
     
  16. spmcgann

    Thread Starter New Member

    Apr 15, 2013
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    The receiver (third party product and not eligible for alteration) can accept any xx.x:1 ratio of inputs. It wants a square wave signal with a minimum of a 2ms pulse which is 5 vdc or better. It doesn't seem to work real well with the 22:1 ratio (+/- 20 error). I've managed to get it down to a 5.5:1 right now using both sides of a 4013 but it is still somewhat erratic (+/- 5 error) and I think I can get better (see the trending relationship between pulses and error?).

    There is no other calibration other than that and no filtering circuits. The input is shielded to reduce noise infiltration and runs through a 250 ohm 100MHz ferrite bead (wrapped once) to reduce the possibility of interference from external RF in the control sub-system.

    The signal input comes from a 4 pole hall effect sensor with a schottky diode and pull-up resistor built in.
     
  17. WBahn

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    Mar 31, 2012
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    That's helpful, but I don't know what, exactly, your inputs to this thing are.

    What does it mean for an input to be 5.5:1? How does the receiver, which has no calibration "other than that" (what is "that"), know what this ratio is?

    Are you sending it two inputs, one from the sensor and one from some reference source?

    When you say +/-20 error, that's +/-20 what? Percent? RPM?
     
  18. spmcgann

    Thread Starter New Member

    Apr 15, 2013
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    I am able to input how many pulses received = how many RPM. "that" refers to the settings of the receiver where I input the pulse / rev.

    My sender output is 4 pulses /rev of the input gear with a 5.5:1 ratio to the output gear so my final output is 22 pulses /rev of the output gear. There is only one input.

    The error is +/- RPM.
     
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