Electronic Level Indicator using LM3914

Discussion in 'The Projects Forum' started by RodneyB, Apr 24, 2015.

  1. RodneyB

    Thread Starter Active Member

    Apr 28, 2012
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    I am trying to make a Level indicator for a see saw. ( I have attached my drawing)

    On the input I have put a 5 K Pot to act as a voltage divider. The Idea is as this is rotated on the see saw the voltage will adjust and the Corresponding LED will light up.

    When I made it the voltage adjusted in a very little of the pot rotation. The LEDs Were erratic some flashing some not coming on and it never could stay on one LED.

    I would like to get them to light in a sequence gradually.

    I would really appreciate some assistance as I can see where I am going wrong.
     
  2. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    There are some things not OK in your schematic.
    I made some comments in your drawing:

    LM3914_Rodney_with comments.png

    Did you read the datasheet?
    LM3914.pdf

    Bertus
     
  3. RodneyB

    Thread Starter Active Member

    Apr 28, 2012
    633
    13
    Thank you

    I will make the changes read the datasheet again and re post
     
  4. RodneyB

    Thread Starter Active Member

    Apr 28, 2012
    633
    13
    Bertus

    I have looked at the datasheet and several circuits on the Internet. I "think" I have adapted it to suit my requirements. The Input voltage is 12 Volts through the voltage divider (RV1 and R1) the minimum voltage is 6 Volts.

    VR1 sets the upper limit whilst VR2 sets the lower limit.

    Because I anticipate the see saw moving quite quickly I have removed 6 of the LED's.

    I would like to know if this circuit is plausible.

    I am concerned that because of the See saw movement of RV1 there should be a 100nF capacitor across pins 1 and 2 of VR1. Is there something more robust that I can use instead of a variable resistor.

    I would also like to use 10Watt LEDs can the outputs of the LM3914 switch Opto isolators.

    Many thanks

    Rodney
     
  5. Reloadron

    Active Member

    Jan 15, 2015
    963
    232
    Using a voltage divider as the power supply really isn't a good idea. Reason being as the chip cycles the current will be constantly changing and bouncing around. Keep in mind that your circuit is in parallel with R1 and part of RV1. The divider out voltage will vary and bounce around. If you want a stable supply you can just use a regulator like a LM7809 for example off the 12 volt battery or any other low dropout type regulator if the battery voltage getting low is a concern. Anyway, I do not see the voltage divider configuration as a good idea.
    Yes, the LM3914 outputs can drive opto isolators, mosfets, and other switching devices.
    Depending on the slew rate of the input voltage with your design there will be "dead" spots while the unused outputs are running in dot mode.

    Ron
     
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  6. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    What voltage range do you want to show on the leds?
    How much current do you want to have for each led?

    The voltage can be adjusted with the voltage reference and the in-high and in-low connections.
    The current for the led is about 10 times the current drawn from the reference voltage pin.

    Bertus
     
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  7. RodneyB

    Thread Starter Active Member

    Apr 28, 2012
    633
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    Because of the see saw motion I thought this was the best choice. Of IC.....

    If I used all 10 of the LED's. The practical application of the circuit would be very confusing.

    The object of the lights on the see saw is to help teach balance.

    I could use limit switches that switch in voltage regulators or relays. To switch on the LED's. At this stage I am not to sure. The LED's are 10 watt I was going to make solid state relays to switch them.

    At this stage any advice on a circuit Will be most welcome
     
  8. RodneyB

    Thread Starter Active Member

    Apr 28, 2012
    633
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    The LEFt's are 10 watts each. I chose to use every second outlet to not confuse things in the practicle application. I did out line other ideas above

    Thanks for the help thus far
     
  9. ScottWang

    Moderator

    Aug 23, 2012
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    767
    Using LM78L09 to be the power source.
     
  10. RodneyB

    Thread Starter Active Member

    Apr 28, 2012
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    If I use the 7809 as a power source and a voltages divider on the signal input Will that work
     
  11. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Again, what voltage levels do you want to show on the leds?

    Bertus
     
  12. RodneyB

    Thread Starter Active Member

    Apr 28, 2012
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    2,4,6,8,10,and 12 volts.
     
  13. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    So you need only 6 of the 10 leds.

    Bertus
     
  14. RodneyB

    Thread Starter Active Member

    Apr 28, 2012
    633
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    Yes only six of the 10
     
  15. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Have a try with the following schematic:

    LM3914_volt_meter_0_20_volt.png

    Bertus
     
  16. RodneyB

    Thread Starter Active Member

    Apr 28, 2012
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    Thank you
     
  17. ScottWang

    Moderator

    Aug 23, 2012
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    If you want to use it as dot level indicator then you can use 78L09, if you want to use it as bar level indicator then you need to use 7809 or 78M09.
     
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  18. RodneyB

    Thread Starter Active Member

    Apr 28, 2012
    633
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    Bertus

    Using your circuit I want to switch a 10 Watt LED light. I have attached the drawing that I think is correct but I need guidance.

    Many thanks

    Rodney
     
  19. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    You do not need resistors for current limiting for the leds on the LM3914, as the current is determined by the 625 ohms resistor in my schematic.

    Bertus
     
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  20. RodneyB

    Thread Starter Active Member

    Apr 28, 2012
    633
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    Thank you very much
     
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