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  1. #1
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    vu meter led bar graph

    good morning sir/madam
    im looking to creat a led bar graph that can show me when the voltage of the power is high or low i used lm3914 and its working when i was a potentiometer but the problem is when i delete this component it doesnt work correctly bceause in reality the voltage of my circuit will turn up and down and i think that i dont need the potentiometer and this is my shematic. the highest voltage is 120v
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    all my regards sir and thanks for helping me

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  2. #2
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    Re: vu meter led bar graph

    if you apply 120v directly to the lm3914 input, there will be smoke ...

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    Re: vu meter led bar graph

    no sir i will not apply 120 v directly to the lm3914 input the 120v i will recieve to the input of first resistor(900k) and i will decrease the voltage to check my bar graph and for the Lm3914 i will apply 9V
    thank you for helping me

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    Re: vu meter led bar graph

    any one help me please??

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    Re: vu meter led bar graph

    you need a diode bridge to rectify your ac signal, then a capacitor to filter it, then a voltage divider with two resistors, and then to your lm3914

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    Re: vu meter led bar graph

    can you help me with schematic??
    and im soory for missunderstanding because my english is not good
    and thank you for interresting

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    Re: vu meter led bar graph

    if you don't know what a diode bridge is, then I don't want you to play with 120v voltages : it can kill you !
    google and wikipedia are your friends on that.

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    Re: vu meter led bar graph

    i know what is it a diode bridge sir and i think that i dont need it because my signal is all time positive its between 0v and 120v

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    Re: vu meter led bar graph

    please somebody help me with shematics

    - - - Updated - - -

    please somebody help me with shematics

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    Re: vu meter led bar graph

    Don't connect Adj to ground
    If your signal is ac rectify and if dc only use voltage divider
    your input signal must be 0<input<adj;

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    Re: vu meter led bar graph

    yes sir my signal is between 0<signal<120v
    thank you again for helping me and i hope that it work in reality because it work fine on isis

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    Re: vu meter led bar graph

    my circuit work fine in isis but when i realize it with real component it doesn't work i don't know where is the problem and this is my circuit
    please anyone help me i need this project so much and theres another problem is when i connect +9 for lm3914 and leds the first 3 leds glow so much and the other leds nver glow with the voltage of the audio amplifer
    all my regards
    Last edited by kik; 28th May 2013 at 17:51.

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    Re: vu meter led bar graph

    Why are you doing stupid things . In my last thread i told you not to ground adj? Follow my schematic

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    Re: vu meter led bar graph

    for audio signals you should use the lm3915 as it changes by log levels. lm3914 is linear and won't be ok
    see here : http://sound.westhost.com/project60.htm

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    Re: vu meter led bar graph

    thank you all for helping me
    but please someone help me with shematic and i wish that this shematic works because really i don't like to give up

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    Re: vu meter led bar graph

    I made a similar project, using a 3914 IC to indicate mains ACV via 10 led's.
    I used a step-down transformer, because I did not believe it is wise to risk exposing components to high voltage.

    The transformer was inside a power supply, obtained at a bargain price from All-Electronics (mail order supply). I had purchased several different wall-warts for a dollar or two each.

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    Re: vu meter led bar graph

    i see that no body can help me to realize my home project
    can i ask you at least to get details about the circuit how can i build something like this using diodes??Click image for larger version. 

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    Re: vu meter led bar graph

    hi,
    what are you going to build? a bar graph voltmeter or a audio vu meter ?

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    Re: vu meter led bar graph

    After buying a 3914 IC, I experimented with it by hooking up ten led's (just like the datasheet shows).

    I made it into a bargraph voltmeter for my car. It took a lot of adjusting and troubleshooting, for me to get it to work right, and for the led's to light up in sequence, in the voltage steps that I wanted them to.
    It should not be hard for you to make the same project. Then after that, you jump from that configuration, to one that measures mains AC (stepped down through a transformer for safety reasons).

    One thing that is worth trying is to get an expanded scale reading. This means that led's light up only when the supply is within a range of, say, 8 to 15 V (for my car).

    Below 6V, no led lights. This gives you higher resolution available in the usual volt range we wish to measure.

    To set a minimum reference volt level, you attach a potentiometer to a particular reference pin (I forget which). Adjust until you find the point where the first led lights when the supply is at the desired volt level.

  20. #20
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    Re: vu meter led bar graph

    im trying to build an audio vumeter and when i measure the voltage it gives me between10Vand 120v and i think that LM3914 can't support this high voltage
    and when i follow the datasheet of lm3915 all leds are lighted when i wire pins and leds and i use the 50k potentiometer
    please somebody help me and if you can please send me the PCB and the isis similation really i feel very tired from this project but the problem is that i need it in my room
    all regards and please help me
    Last edited by kik; 9th June 2013 at 15:27.

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