Measuring Hall-Effect switch pulse frequency

Discussion in 'General Electronics Chat' started by Diversitile, Apr 10, 2015.

  1. Diversitile

    Thread Starter New Member

    Apr 10, 2015
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    So I have a Hall-effect switch type flow-meter that gives out short square wave pulses proportionally to the amount of flow, roughly 0 to 1000 pules per minute. I need to find a way to measure this frequency in order to get some data out of that flow-meter. I have seen similar projects involving Arduino, but I don't own one nor do I want to spend that much money. Is there a simple device that can count these pulses or perhaps some circuit that I can assemble?
     
  2. MrChips

    Moderator

    Oct 2, 2009
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    If you don't want to spend any more money, check your handheld DMM and see if it can measure frequency.

    [​IMG]
     
  3. Diversitile

    Thread Starter New Member

    Apr 10, 2015
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    That's a good idea. But I thought that those things can only measure AC frequency, how will it cope with few DC pulses?
     
  4. dl324

    Distinguished Member

    Mar 30, 2015
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    It's worth a try if you already have a meter that measures frequency, but success depends on what the meter considers "periodic" and the algorithm used.
     
  5. Diversitile

    Thread Starter New Member

    Apr 10, 2015
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    I don't have one, but could try to borrow one.
    By the way how hard would it be to hook it up to some kind of microcontroller + lcd ? Don't see other options...
     
  6. dl324

    Distinguished Member

    Mar 30, 2015
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    Best to try before you buy...
    Possible solutions depend on what you want to do. Describe what you want and then people can give you suggestions.
     
  7. Diversitile

    Thread Starter New Member

    Apr 10, 2015
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    Well it's a water flow meter and I need to compare some water pump flow rates. I have the hall sensor but I don't have the corresponding digital hand-held meter. DMM would be the easiest solution.
     
  8. dl324

    Distinguished Member

    Mar 30, 2015
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    Sounds like this is a manual operation. Change pump, check flow rate with Hall sensor. You could use a simple 3 decade counter; or a universal counter if you want an off the shelf solution.
     
  9. alfacliff

    Well-Known Member

    Dec 13, 2013
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    in the old days, when things were simple, I would say use an integrator circuit, chargng a cap through a resistor, a tachometer circuit. if you go with an arduino or similar, count from the start of one pulse to the strart of the next, it works better than counting pulses directly. a counter with a fixed pulse rate from the clock gated on and off by the incoming pulses, works much better at lower frequencies.
     
  10. Diversitile

    Thread Starter New Member

    Apr 10, 2015
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    Should have been more precise. In the end I still need to get ~5% accurate flow rate number so I can get a curve of flow-rate according to pressure.
    I don't think that a counter could do that.

    I should probably also mention that I have basic knowledge of electronics, but can easily make a electronic circuit if I have a scheme.
     
  11. alfacliff

    Well-Known Member

    Dec 13, 2013
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    thats the reason for counting a fixed pulse train, it it is running at a fairly high rate, and your hall effect pulses are slow, you will get a higher count. for instance 10 pulses per second from the hall detector, gating a 1000 hz pulse on, then off at the next pulse giving you a count of 100. the arduino and others can be setup to give you the count pulses and to gate them with the incoming hall detector pulses.
     
  12. Diversitile

    Thread Starter New Member

    Apr 10, 2015
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    I think I have come up with an easier solution.
    What if I just use an old bicycle computer? Those work with reed switches, but I could modify the circuit to work with hall effect switch. Just add power supply to hall switch and connect output from it to the base of the transistor. That should emulate reed switch, atleast in my mind.
    Will that work?
     
  13. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    That should work, provided the supply voltages for the Hall switch and computer are compatible.
     
  14. Diversitile

    Thread Starter New Member

    Apr 10, 2015
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    Is this how it should look like?
    And extra question - why is there often an R1 resistor on hall effect circuits?
     
  15. Diversitile

    Thread Starter New Member

    Apr 10, 2015
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    Does that matter in my case at all?
     
  16. Reloadron

    Active Member

    Jan 15, 2015
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    The image you posted shows R1 as a pullup for an open collector output. In that scenario the pulses will be about 5 volt amplitude so if 5 volts is fine than things should be fine.

    Ron
     
  17. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    R1 is a pull-up resistor so that the Hall output can switch between 5V and ground.
    If you use the circuit as per post #14 then there will be no supply incompatability problem. If, on the other hand, you were to drive the computer directly from the Hall output and that output could pull up to 5V then there could be a problem if the bike computer supply were only 3V, say.
     
  18. Diversitile

    Thread Starter New Member

    Apr 10, 2015
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    So I am putting things together and wondering how exactly do I calculate transistor's base resistance (R2)? Using circuit as per post #14, hall sensor supply 9V, bike's computer supply 3V and using BD139 transistor.
     
  19. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    R2 isn't critical. Anything in the range 2k2-47k, say, would probably do.
     
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