Tachometer

Discussion in 'The Projects Forum' started by FroceMaster, Aug 11, 2014.

  1. FroceMaster

    Thread Starter Member

    Jan 28, 2012
    400
    4
    Hi
    Have to make a tachometer
    5 inputs . 0-300 rpm.
    Lcd out.
    Microchip 16f690 or.
    What type of hardware to read the rpm from the rotating shaft

    I think when i have the hardware in place the software should not be a problem

    Can some come with some inputs ?
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    What can you mount on the rotating shaft? A disc? a mirror? a magnet? Paint?
     
  3. wayneh

    Expert

    Sep 9, 2010
    12,083
    3,022
    A small magnet spinning with the shaft allows using a hall effect sensor. Another option is to use an optical detector, such as a small reflective patch that can return a light beam into a fixed sensor. Or pass a beam thru a notch in a disc that rotates with the shaft, or conversely a tab that blocks a beam at each rotation. Lots of options.
     
  4. FroceMaster

    Thread Starter Member

    Jan 28, 2012
    400
    4
    MAgnet should be possible cause it's iron.
    Hall effect sensor ???
    should be mounted on shaft 5-10 m, from the readouts.
    in some very dirty invirmoent.
    Dronningborg harvester.
     
  5. FroceMaster

    Thread Starter Member

    Jan 28, 2012
    400
    4
    can i have 5 inputs in one 16f690 ?
    or do i need 5 chip ?
     
  6. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I tend to use the slot optos they have both TX and RX in one.
    For the hall effect I use the Honeywell SS400 series, there are also hall effect that just read a ferrous metal flag, no magnet required.
    If you use a PIC with CCP capture input for T1, it comes with edge capture features, every rising/falling/both edges etc.
    What is meant by 5 inputs in one?
    Max.
     
  7. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Are there any sprockets or toothed gears already mounted on the shaft in question?
     
  8. FroceMaster

    Thread Starter Member

    Jan 28, 2012
    400
    4
    have 5 shafts to monitor, and output to one lcd.
     
  9. FroceMaster

    Thread Starter Member

    Jan 28, 2012
    400
    4
    Do not know, have not checked.
     
  10. wayneh

    Expert

    Sep 9, 2010
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    Does this mean the sensor will be exposed to the elements, for instance pressure washing and such?

    Are you measuring the rotation of each of those shafts at the front of the machine, the ones you can observe from outside? Aren't they linked together? Just trying to understand what your goals are.
     
  11. FroceMaster

    Thread Starter Member

    Jan 28, 2012
    400
    4
    have 3 elevators, in the middle of the machine,
    and a couple of others we also want to check, while machine is working.

    some drivebelt can miss the traction and that's why we will monitor them.
     
  12. MaxHeadRoom

    Expert

    Jul 18, 2013
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    So it is a multiplex operation?
    Max.
     
  13. wayneh

    Expert

    Sep 9, 2010
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    So you have drive pulleys on each shaft? Do you also have access to the end of the shaft itself? Will the sensors have to withstand rain, pressure washing, abrasion from corn, flying dirt, etc.?

    A photo of the working environment would be helpful; the shaft, its end, any pulleys and so on.
     
  14. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,963
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    You can use one PIC, and scan the inputs take a reading from each input,and store them in memory.

    Best way would be to use the T1 timer as a counter(pin2), and count the pulses in 1 second, then multiply it by 60 and display it in RPM,or (have six sensors per shaft and multiply by ten, more accurate reading )
    all sensors use the same input T1, multiplex them using a CD4016 quad switch chip, other members will have their own ideas as well to help you.
     
    Last edited: Aug 12, 2014
  15. FroceMaster

    Thread Starter Member

    Jan 28, 2012
    400
    4
    Hi,
    The output from the 4 gates in 4016, can i just put them togheter or do i need ex another chip, like a CD4072B OR 4 input. ??
     
  16. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,963
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    Just use the cd4016 as a quad switch, make the enable pin on each gate high when you want to read that sensor, the others make low, so it only reads that one sensor, put all inputs to the same pic input (pin2) like this, for more sensors use another 4016 chip.
     
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  17. FroceMaster

    Thread Starter Member

    Jan 28, 2012
    400
    4
    Hi
    That will say that the output from 4016 is floting, when not enable. ?
    Can that be right ?
     
  18. cork_ie

    Member

    Oct 8, 2011
    348
    58
    If this machine is a harvester then , it will be hot dusty and dirty and you are unlikely to get reflective tape or paint to work for any prolonged period. I have done a few of these kinds of projects, but always with only one or two pulleys or sprockets.
    Best method is to drill a and tap a small 5mm hole somewhere on the pulley and screw in a small set screw so that the screw head will act as a little peg. If you use a little "stud lock" or similar thread locking adhesive it will never move once fitted.
    Once you have your peg, on each pulley or shaft then it is a simple matter of using a standard automotive magnetic coil or Hall type pickup, mounted with approximately 1mm clearence from the peg.
     
  19. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,761
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    If that is a concern then you can use a weak pull-up on the PIC input.
     
  20. FroceMaster

    Thread Starter Member

    Jan 28, 2012
    400
    4
    I now have this cooked.
    output.png

    Will use some inductive sensors that will react on metal, then i just add a litte bolt on the sprocket, or 6.
    have made it with capability of 8 sensors, but just for future maybee.

    Will use a 16F690 and connect it all as shown,
    Will that be working, or do i need some extra pull ups or caps or ?
    The pic should then read the timer, switch to another shaft, and Count Again.
    if any shaft not rotating at the lower limit an alarm will be set.
    for that i will use ex RC3 cause it's free.
    how to i make it pull a relay at 14v 100mA ?
     
    Last edited: Aug 17, 2014
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