Problem with LED voltmeter

Discussion in 'General Electronics Chat' started by kvsingh21, Aug 4, 2008.

  1. kvsingh21

    Thread Starter Active Member

    Apr 15, 2008
    63
    0
    I am trying to insert a led voltmeter in my circuit to obtain output voltage, but cant get it to work.:(

    This is the Voltmeter
    http://www.lascarelectronics.com/pdf-usb-datalogging/data-logger0052334001208961058.pdf

    I should have a positive output of few volts (tested on oscilloscope), and measured relative to ground.

    I cant figure out which pins needs to be grounded, left floating etc. (expect the obvious power supply pins), especially the relative voltage pins.

    Any help will be really appreciated.
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,647
    2,346
    Hello,

    All information can be found in the datasheet.
    Pin 2 is a Positive powersupply.
    Pin 1 is a negativ powersupply.
    Pin 4 is ground / zero reference for voltmeter.
    Pin 3 is the input for the voltmeter.
    Pin 5 and Pin 6 need to be connected for the reference voltage.

    Input is standard 200 mV full scale, this can be scaled up using resistor divider according to the tabel given in the datasheet.

    Greetings,
    Bertus
     
  3. kvsingh21

    Thread Starter Active Member

    Apr 15, 2008
    63
    0
    Thanks for your reply bertus.
    But i dont know what the reference voltage is meant to be. Is it the same as supply:confused:
    Also i am planning to connect pin 11 to pin 12. So should i leave pins 9 and 10 floating, or ground them?
     
  4. bertus

    Administrator

    Apr 5, 2008
    15,647
    2,346
    Hello,

    You can connect 11 to 12 and leave 9 and 10 open, they have internal resistors.
    The reference can be set with the potmeter at the rear of the module.

    Between pin 1 and 4 should be at least 1.6 Volt, as said in the datasheet.
    So pin 1 is connected to a negative powersupply.

    Greetings,
    Bertus
     
  5. kvsingh21

    Thread Starter Active Member

    Apr 15, 2008
    63
    0
    Thanks for your reply mate.

    The problem is that i dont have a negative power supply. All i have is a 12V battery with one terminal connected to supply rail, and the other one to ground. And then i have a positive voltage that i need to measure with respect to ground. So what do you suggest mate?
     
  6. Wendy

    Moderator

    Mar 24, 2008
    20,765
    2,536
    Is your base power supply floating (as in no ground)? Check this thread out.
     
  7. kvsingh21

    Thread Starter Active Member

    Apr 15, 2008
    63
    0
    The base power is +ve 12V, and -ve 0V i.e ground.
     
  8. bertus

    Administrator

    Apr 5, 2008
    15,647
    2,346
    Hello,

    Is the voltage you try to measure connected to -ve ( 0 Volt )?
    The meter expects the lower input at (at least) 1.6 Volt.

    Greetings,
    Bertus
     
  9. kvsingh21

    Thread Starter Active Member

    Apr 15, 2008
    63
    0
    Hi Bertus,
    Yes the voltage is connected to O V. I noticed that in your previous post as well. You reckon there is a way round all this. I will post pics of my circuit once i get home.
     
  10. kvsingh21

    Thread Starter Active Member

    Apr 15, 2008
    63
    0
    Hers my circuit. The multimeter is being replaced by LED voltmeter.

    [​IMG]
    [​IMG]
     
  11. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    The meter is designed to be powered from a 9V alkaline battery that has no connections to ground or to the input. A separate 9V power supply can be used instead of the battery.

    The meter measures DC voltage but your circuit has an AC output voltage. You will need to make a precision rectifier circuit to convert low level AC to DC.

    The voltmeter uses a low current LCD display, not a high current LED display. It will be invisible at night.
     
  12. kvsingh21

    Thread Starter Active Member

    Apr 15, 2008
    63
    0
    Thanks mate, it makes sense.
    Any particular circuit you would recommend for rectifier.

    Visibility is not a problem, will only need it in day.
     
  13. kvsingh21

    Thread Starter Active Member

    Apr 15, 2008
    63
    0
    I have connected a full wave rectifier to convert AC to DC, which is then the input for LCD voltmeter. I am using a 9V alkaline battery as power supply. But its still not functioning properly.

    This is the way i connected pins. PLease tell me if they are right , wrong etc.

    1) Negative terminal of 9V alkaline battery
    2) Positive terminal of battery
    3) Positive DC output from rectifier
    4) Negative output from rectifier
    5, 6) Connected to each other.
    7,8,9,10) Unconnected.
    11,12) connected to each other
     
  14. bertus

    Administrator

    Apr 5, 2008
    15,647
    2,346
    Hello,

    If you are using a 9V battery to power the meter, you can use the "floating" diagram from the datasheet.

    1) Negative terminal of 9V alkaline battery
    2) Positive terminal of battery
    3) Positive DC output from rectifier
    4, 5, 6) Connected to each other. Negative output from rectifier
    7,8,9,10) Unconnected.
    11,12) connected to each other

    Greetings,
    Bertus
     
  15. kvsingh21

    Thread Starter Active Member

    Apr 15, 2008
    63
    0
  16. bertus

    Administrator

    Apr 5, 2008
    15,647
    2,346
    Hello,

    That could do the job if the voltage you want to measure is over 6.5 Volts.

    Greetings,
    Bertus
     
Loading...