LM2907 problems. I cannot make it working. Always display 0 on voltage.

Discussion in 'General Electronics Chat' started by davidbr, Apr 25, 2018.

  1. davidbr

    Thread Starter Member

    Apr 25, 2018
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    Hello all,
    This is my first post here and please be gentle if I do some mistakes :)

    So my problem is :
    I want to measure speed of 2 wheels using arduino.
    Maximum speed which is not possible to reach is about 6.6 km/h , which means around 700 rpm and 12Hz as frequency.
    Minimum speed which I want to measure is around 60 rpm which is 1Hz. So whatever is below 1Hz I will consider "0".
    Wheel has 25mm radius, and has on it 4 oles, each 2 holes opposite. Basically I need 4 pulses for a complete revolution.
    For getting pulses I am using a proximity sensor which has 12V pulse when is on the whole and 0V when is not on the hole.
    The wheel and sensor pictures are attached
    I tried schematic from datasheet and also tried this schematic as well http://bettec.info/dro/
    On both I get only 0 at the output no matter the rpm is...

    Thanks you in advance
     
  2. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Do have an actual true/proper schematic showing exactly how YOU have it wired/powered to your arduino.?
    Not someone elses.. What you actually have..
     
  3. davidbr

    Thread Starter Member

    Apr 25, 2018
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    I haven t yet wired to arduino, I just measured voltage between output of LM and ground.
    I tried 2 versions, first is one from this link http://bettec.info/dro/ (variant with 8 pin LM) and second the one from datasheet from minimal tacho example.
    If is working then voltage should vary if i speed up the wheel...so as long I have 0.02V all the time I am assuming that my circuit will not work..
    Or maybe I misunderstood your question?
     
    Last edited: Apr 25, 2018
  4. dendad

    Distinguished Member

    Feb 20, 2016
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    Do you get the internal LED on the proximity sensor (prox) working?
    This prox is probably an open collector type so....
    The prox most likley needs a pullup resistor to work so add a 2K2 resistor between the + and output then see if you get pulses. For running into an Arduino, connect the pullup from the output to the +5V supply, not the prox supply. Ensure the pulses to the Arduino do not go over 5V.
    And it will work better with more pulses per turn I think. The response will be smoother.
     
  5. davidbr

    Thread Starter Member

    Apr 25, 2018
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    Hi,
    The led on the sensor is working. While output is 0V the led is on and while output is hight(sensor is in hole) the led d off.
    I will try add pull up resistor on the sensor output...
     
  6. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    You can't test it that way..
    Its an open collector (NPN) and needs to be interfaced properly..
    Sounds like its working you just aren't doing a suitable test
     
  7. davidbr

    Thread Starter Member

    Apr 25, 2018
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    And which will be a good interfave and proper test?
    Yes, sensor is npn
    Thanks
     
  8. dendad

    Distinguished Member

    Feb 20, 2016
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    Why are you using an LM2907 FtoV converter when the Arduino can be used to measure the pulse frequency or period?
    It is just a thought,
    I supose measuring a voltage is a bit easier.
     
  9. crutschow

    Expert

    Mar 14, 2008
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    You need to show us a complete schematic including how the sensor is wired.
     
  10. davidbr

    Thread Starter Member

    Apr 25, 2018
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    I really want measure voltage. So that is about this post.
     
  11. dendad

    Distinguished Member

    Feb 20, 2016
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    Did you try a pullup resistor yet to make sure pulses are comming out?
     
  12. davidbr

    Thread Starter Member

    Apr 25, 2018
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    I will try tommorrow, i am not at the office anymore....
     
  13. dendad

    Distinguished Member

    Feb 20, 2016
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    ok.
    It is 1:30AM here so I should be asleep. Good night all.
     
  14. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    As stated 5V pullup resistor..
    See third image in the "open collector" section here..
    https://github.com/PatternAgents/Electronics_One_Workshop/wiki/Logic-Circuits
    "Out" will go high/low in response to your holes and that can easily be read directly by the arduino using digitalread(),etc...
     
  15. davidbr

    Thread Starter Member

    Apr 25, 2018
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    Ok,
    Attached is the schematic that I did, and I followed exactly the values from here (lm2907.png).
    The sensor is wired like this : Brown to +12V, Blue to GND and Black to PIN1 of LM.

    I measure between +Vout and GND.

    I tried also with 2k2 resistor between Black and Brown of the sensor and get same result.
    What I am thinking is why on the schematic is on +Vout value 67Hz /V ? In my tests I don t think I go up about 10 Hz ...maybe I should use different values on components?

    Thanks again
     
  16. davidbr

    Thread Starter Member

    Apr 25, 2018
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    I cannot edit but I saw that in first post i made a mistake:

    "Maximum speed which is not possible to reach is about 6.6 km/h , which means around 700 rpm and 12Hz as frequency.
    Minimum speed which I want to measure is around 60 rpm which is 1Hz. So whatever is below 1Hz I will consider "0"."
    Considering I get 4 pulses for revolution that means my freq are between 4Hz and 48Hz not like I said in first post
     
  17. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    There is no resistor needed from the brown to black, as there is a 4k7 resistor in the sensor.
    Do you see pulses at the output of the sensor?
    The datasheet shows me that the sensing distance is 4 mm for your sensor.

    Bertus
     
  18. davidbr

    Thread Starter Member

    Apr 25, 2018
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    Yes I can see pulses. I can measure output of the sensor and also it has a blinking led .
     
  19. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Is the led permanent connected?
    Is there a resistor in series with the led?

    Bertus
     
  20. davidbr

    Thread Starter Member

    Apr 25, 2018
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    I am talking about sensor led which is on when I have sensor out of the hole and 0 on output. When sensor is in hole, then led is off and I have 12v on output
    see picture
     
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