LM3914 as LED driver for meter circuit help

Discussion in 'The Projects Forum' started by Butterworth, Jul 11, 2011.

  1. Butterworth

    Thread Starter Active Member

    May 6, 2009
    135
    3
    I found this link on google for a VU meter that utilized the LM3914. Ron H brought this IC to my attention after working out the glitches on my EMF Meter schematic posted here.

    The idea behind this is to have an led readout of the amplified signal produced when using the EMF meter, but I wanted to know if this schematic will work for my application? If it should work then I need to know if I can hook up the input to the meter + & - leads, or if there are better spots to do this?

    Thanks to all for your help.
     
  2. Butterworth

    Thread Starter Active Member

    May 6, 2009
    135
    3
    bump..... Please, I would like some help on this.
     
  3. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,750
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    The schema u posted has an input rectifier which will decrease sensitivity by a lot.

    First measure the voltage variation of ur EMF meter output.
    The minimum and maximum values are needed find the values of the components to display full scale in the VU meter.
    the LM3914 has a linear variation and I think is suitable for ur needs But it might need an active full wave rectifier to eliminate loss.

    Using passive rectifies will introduce a 0.2V min for a Ge diode and 0.7V for a Si diode.
    Which will hinder low level indications.
     
  4. Butterworth

    Thread Starter Active Member

    May 6, 2009
    135
    3
    Ok, I can grab the voltage off of the meter input (+/-) I assume?

    The schematic was an idea, can I get away with removing the series resistors prior to the LED's?
     
  5. #12

    Expert

    Nov 30, 2010
    16,261
    6,774
    This datasheet seems to indicate that the 3914 has an LED current settng resistor, but you are welcome to examine it yourself.
     
  6. Butterworth

    Thread Starter Active Member

    May 6, 2009
    135
    3
    As I was leafing through the data sheets again, I found one of their examples of a typical application where the bar style led set up has reached the top end of the referenced signal, all of the leds will flash as an "alarm". See the attached snip of the data sheet.

    I like this option, could I use this as it is shown? I am not that good with the math of this kind of stuff, but I learn quick!
     
  7. iONic

    AAC Fanatic!

    Nov 16, 2007
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    The previous schematic doesn't mention the voltage range it will display. We also do not know the voltage range you want to monitor.
     
  8. Butterworth

    Thread Starter Active Member

    May 6, 2009
    135
    3
    Yes I still have to monitor that when the meter circuit is in operation. Once I have that, it will give the base numbers to work towards?
     
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