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    Basic 12v Battery VOLTAGE METER, more resolution needed

    Hello,
    I am trying to use ( LM3914 ) like this:
    https://circuitdigest.com/electronic...tmeter-circuit

    As a voltage meter, lighting LED one at a time based on voltage.

    My question is, the way the circuit is normally setup is to light each LED per 1.5v 'steps' give or take

    What I want it to do instead, is only show me from say 10v to 14v range, instead of 0-15v range.
    In other words I'd like more resolution between 10 and 15 volts and to basically ignore the 0-10v range (because the battery never goes that low)

    I am trying to use it to show whether the in-car alternator is working or not. Alternator puts out 14v~ when charging and only battery voltage (10-12v depending how dead it is) when the alternator fails.


    thanks for looking!

    - - - Updated - - -

    I found this and I think it answers my question, will update when I produce a project
    http://www.k7tty.com/development/ele...your%20Car.htm

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    Re: Basic 12v Battery VOLTAGE METER, more resolution needed

    There are 7-Segment Voltmeter kits with 3-Digits at aliexpress.The cost is lower than what you do by yourself



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    Re: Basic 12v Battery VOLTAGE METER, more resolution needed

    Quote Originally Posted by BigBoss View Post
    There are 7-Segment Voltmeter kits with 3-Digits at aliexpress.The cost is lower than what you do by yourself
    Can you please elaborate, I am new to all of this....

    I see tons of them and trying to make sense of it

    You mean this by any chance?
    https://www.aliexpress.com/item/4000...chweb201603_53


    Sorry it takes me a minute

    - - - Updated - - -

    So for something like this
    https://www.aliexpress.com/item/3281...a-421ff4be4687

    Click image for larger version. 

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    I notice some kind of adjustment on the back, I think its for resolution? using at lower voltage?

    Other question is, I notice the load ground going through the amp-meter. Does that mean it MUST act as a sink for the 10A of current? OR are they simply not showing the actual GROUND for the load going somewhere else...

    thanks for the heads up btw

    Right now I'm thinking I will use one for voltage and also measure the amperage of my fuel injectors or something like that. Just for the heck of it. The device is $1
    But I'm curious if there is some other, larger use for the amp-meter that I am not thinking of. I can't use it for the alternator charging current (100amps) clearly. Or the fuel pump (15amps+). Or starter (300amp?)



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    Re: Basic 12v Battery VOLTAGE METER, more resolution needed

    Your k7tty.com link appears suitable to provide expanded scale. I built similar voltmeters. It has instant response to voltage. I can see where it drops to in the first 1/10 of a second when cranking the engine. Thus it tells me something about battery health.

    I adjusted mine to yield a range of 7 to 16V in steps of 1V. (Two or more 3914 IC's can be cascaded for closer resolution.)

    I know of no other type of meters that gives such instant response, neither my old-fashioned D'Arsonval needle type nor digital type.



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    Re: Basic 12v Battery VOLTAGE METER, more resolution needed

    I notice some kind of adjustment on the back, I think its for resolution? using at lower voltage?...
    No, it won't work; because the driver for the display takes the power from the same battery and the ground is common.

    You need to have an offset (say 10V) and then apply the voltage to the input. The ground is common...

    Let us say you put a 10V zener and a 10K resistor to the battery; The voltage across the resistor will now be reduced by 10V.



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    Re: Basic 12v Battery VOLTAGE METER, more resolution needed

    Quote Originally Posted by BradtheRad View Post
    Your k7tty.com link appears suitable to provide expanded scale. I built similar voltmeters. It has instant response to voltage. I can see where it drops to in the first 1/10 of a second when cranking the engine. Thus it tells me something about battery health.

    I adjusted mine to yield a range of 7 to 16V in steps of 1V. (Two or more 3914 IC's can be cascaded for closer resolution.)

    I know of no other type of meters that gives such instant response, neither my old-fashioned D'Arsonval needle type nor digital type.

    This is a great thing to hear. Thank you. I Want to make one of these. I have several chips so I may just string couple together to get a ~0.5v resolution give or take. that'd be nice.

    questions abound
    I wonder how some of the circuit components work. For example the H1 (inductor) on the input, "choke". To protect from high transient spikes.

    I don't have this item, I've never used an inductor before, how do I tell using electrical knowledge exactly how important it is or how it works in this instance? Is there a calculation I can do on paper for this sort of thing- of course there is. But I am not handy with that. What are your thoughts if you don't mind me asking on these type of improvements?

    - - - Updated - - -

    Quote Originally Posted by c_mitra View Post
    No, it won't work; because the driver for the display takes the power from the same battery and the ground is common.

    You need to have an offset (say 10V) and then apply the voltage to the input. The ground is common...

    Let us say you put a 10V zener and a 10K resistor to the battery; The voltage across the resistor will now be reduced by 10V.
    I'm not sure you understood what I meant. On the back of these devices is typically a little adjustment knob that you turn with a screwdriver.

    I just wanted to know what it is for. the instructions I found online do not mention it, at least thus far



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    Re: Basic 12v Battery VOLTAGE METER, more resolution needed

    Its a long time since I used an LM3914 but I think it's possible to lift the bottom of the divider chain above ground to set the minimum reading. The LEDs then display linear steps from bottom to top of the divider chain. The internal reference can be adjusted up to 12V but I think, and it isn't clear from the data sheet, the reference can be disconnected and a higher voltage applied to the top of the chain. So fixing 10V at the bottom and 15V at the top might be all you have to do. I think all the inputs are OK to to about 25V.

    Brian.
    PLEASE - no friends requests or private emails, I simply don't have time to reply to them all.
    It's better to share your questions and answers on Edaboard so we can all benefit from each others experiences.



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    Re: Basic 12v Battery VOLTAGE METER, more resolution needed

    Its a long time since I used an LM3914 but I think it's possible to lift the bottom of the divider chain above ground to set the minimum reading.
    There is one example in the application notes that can be used to set the lower point (the voltage needed to light up the first LED) and also the steps for the next LED.



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