lm3914 20 led voltmeter adjustable range

Discussion in 'The Projects Forum' started by smilem, Aug 19, 2010.

  1. smilem

    Thread Starter Active Member

    Jul 23, 2008
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    Hi, I'm struggling to make 20 red led lm3914 voltmeter.

    I have put together this schematic (lm3914 dot mode) that works (in simulation).

    Meas1 - this is the voltage that will be measured 0-12V
    PSU1 - this is the lm3914 circuit power supply 12V

    see attachment for schematic diagram.

    I would like to:

    1. add lower scale limit Potentiometer (my intended range 0-12V)
    2. add upper scale limit Potentiometer (upper limit is ~12V)
    3. add LED brightness Potentiometer

    Thank you for your time
     
  2. marshallf3

    Well-Known Member

    Jul 26, 2010
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    All the formulas to calculate those are in the spec sheets.
     
  3. soda

    Active Member

    Dec 7, 2008
    174
    13
    I add a diagram which i copy from a ETI mag. It's only for a 10 led display but maybe it can help you see where to place the presets
     
  4. smilem

    Thread Starter Active Member

    Jul 23, 2008
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    I also found this site http://www.seekic.com/forum/22_circuit_diagram/13122_BARGRAPH_CAR_VOLTMETER.html

    This seems to be the same thing.
    But both contain a bug, The one I posted above has unneeded wire from pin 9 to 8, your schematic has wrong wire from pin 9 to 11. If the connection is not removed the last LED does not light. The pin 9 can be connected to pin 3 (bar/dot) mode change but not to the one of the LEDS.

    I'm still looking how to make 20LED meeter with upper lower limiting. Will post some schematics later, hope somebody can help me.
     
  5. marshallf3

    Well-Known Member

    Jul 26, 2010
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    Seriously, it's in the data sheet. http://www.national.com/ds/LM/LM3914.pdf

    The capability of cascading them into a 20 is in one circuit, how to implement the other capabilities you're wanting are shown in other app notes all on that same sheet.

    All you provide is a calculator.
     
  6. soda

    Active Member

    Dec 7, 2008
    174
    13
    smilem,

    Did you test the diagram i showed you because i did and it work quit well on dot mode. To be honest I'm using in my auto tester and i build more for some friends of mine and none of them had any complains
     
  7. smilem

    Thread Starter Active Member

    Jul 23, 2008
    132
    0
    Yes here is the bargraph circuit in my simulator.
    without wire between pin 9 and 11 it works, with it I have problems.

    For some reason I had to change variable resistors from 4.7k to 5k (15V led 10) and 40K (12V led 1).
     
    Last edited: Aug 22, 2010
  8. smilem

    Thread Starter Active Member

    Jul 23, 2008
    132
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    I tried to extend the circuit above to 20 leds, but for some reason led 10 stays always on if voltage is above it's limit. In bar mode you can't notice it but it's clear in dot mode.

    I tried to find the error to no avail. Please see attachment.
     
  9. soda

    Active Member

    Dec 7, 2008
    174
    13
    Check out the data sheet for the lm3914. I think they talk about this problem in the dot mode section of the data sheet
     
  10. smilem

    Thread Starter Active Member

    Jul 23, 2008
    132
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    Do you mean this:

    I tried to connect IC1 Pin 9 to Pin 1 IC2 and this turns off led 10. But it never turns ON.

    I tried to connect IC2 Pins 9 to pin 11, but that makes IC2 last Led 20 always off and led 10 still does not work on IC1.

    I have the 20k resistor as documented in PDF.
     
    Last edited: Aug 23, 2010
  11. marshallf3

    Well-Known Member

    Jul 26, 2010
    2,358
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    Ever try it in real life? I can't see how these circuit simulators can perfectly duplicate anything that's rather out of the ordinary.
     
  12. Audioguru

    New Member

    Dec 20, 2007
    9,411
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    The datasheet says exactly how to connect two LM3914 ICs in a sequence.
     
    smilem likes this.
  13. smilem

    Thread Starter Active Member

    Jul 23, 2008
    132
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    I have made another schematic more easy to read, but still same problem with led10.
    20k resistor is connected to 1st LM3914 as shown in datasheet diagram.
    LM3914 IC1 mode pin 9 connected to LM3914 IC2 pin1 as shown in datasheet diagram, then a wire goes to led 11.

    The led 10 is extinguished as data sheet said, but now how to turn it back on?
     
  14. marshallf3

    Well-Known Member

    Jul 26, 2010
    2,358
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    Chunk your stupid simulator circuit and just follow the manufacturer's instructions as I posted shortly after this thread was started.

    There's no way your new-fangled computerized wang-doodle is going to understand the way the manufacturer solved the problem, that or they didn't bother to write it into their coding.
     
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  15. smilem

    Thread Starter Active Member

    Jul 23, 2008
    132
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    The simulator isn't free or cheap either - 137$
    http://www.maplin.co.uk/Module.aspx?ModuleNo=46480

    I tried it in ISIS and same thing, two manufacturers who can't code right?
    I can say the same about the manufacturer whose chips are all being used in bar mode because they don't work in dot mode. Go on search google, find me some schematics of somebody who successfully made it

    I searched for 2 hours and found dozens of car, boat, etc. circuits all in bar mode, but none for dot mode. A few circuits were however found but they don't work at all., wrong ground pin connections etc.

    People if you are to lazy to draw a few wires with pain (yes I know it is improved in vista/w7) then don't bother posting non helpful posts.
     
  16. marshallf3

    Well-Known Member

    Jul 26, 2010
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    If I had a couple of the chips handy I'd build the circuit this weekend, I'm just saying that they can't take everything into consideration when they build and code those synthesis programs. It's been my experience that when a firm as big as National goes to the trouble of even explaining why it happens and how they dealt with it then they'e apparently addresed the problem in real life situations.
     
  17. smilem

    Thread Starter Active Member

    Jul 23, 2008
    132
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    So you say that my last circuit is correctly wired for dot mode operation and should work right? I'm afraid to damage the chips, they are not that cheap over here. Are resistor values ok?

    As I said signal input will be 4 to 9volts, power will be 12v.

    Thanks.
     
  18. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    I buy genuine National Semi LM3914 or LM3915 ICs in a local surplus electronics parts store for $1.00 each, the same as one litre of gasoline.
     
  19. smilem

    Thread Starter Active Member

    Jul 23, 2008
    132
    0
    1 litre of gasoline costs 1.46$

    LM3914 price is 3$, leds matrix cost about 1.50$, so that makes about 9$ without resistors etc. Total project cost is about 20$ not cheap for 20 led indicator if you ask me.
     
  20. MMcLaren

    Well-Known Member

    Feb 14, 2010
    759
    116
    May I ask why you need 20 LEDs instead of 10 LEDs Sir? And what did you say the application was?
     
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