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    How to create a voltage selector circuit

    Hi I want to make a voltage selector circuit with opamps and diodes etc. (no IC's except opamps) but I couldn't find a way, do you have any advice for me ? Its like a dot display level meter (dot not bar) but I can not use LM3915 etc.

    I have a varying DC voltage and want to make a circuit that choose a specific path for its amplitude. I don't need to save dc input I don't need its information, I only want to know its amplitude Voltage range

    Like if dc source has 0-1V current flow goes path 1, if it has 1-2V current flow goes path2, if it has 2-3V current flow goes path3 etc. But when it goes from path 3, it cannot goes through path 1 and 2.

    I know that I will use comparators but couldn't find a logical connection which will stop unneeded paths.

    (Paths will not be open circuited as I show it on image there will be more connections to them by using buffers.)

    Thanks
    Click image for larger version. 

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    Re: How to create a voltage selector circuit

    Hi,

    Unclear, uncomplete informations.
    A black box with some lines...
    I don't know what this means.

    If I'd select the current flow .... I'd try an analog switch/MUX.

    Klaus
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    Re: How to create a voltage selector circuit

    Try to devise XOR gates (exclusive-OR). A stack of them creates a one-dot graph effect as you need.

    I suppose you realize you could start with a window comparator made from several op amps. This makes a bar graph, however this method turns on several indicators at a time. So you also realize you need to add a method to select one and only one indicator.

    XOR circuits made from transistors can be seen at the website below. It may be possible to adapt these to your design.

    http://www.4qdtec.com/dlc.html



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    Re: How to create a voltage selector circuit

    Quote Originally Posted by KlausST View Post
    Hi,

    Unclear, uncomplete informations.
    A black box with some lines...
    I don't know what this means.

    If I'd select the current flow .... I'd try an analog switch/MUX.

    Klaus
    Quote Originally Posted by BradtheRad View Post
    Try to devise XOR gates (exclusive-OR). A stack of them creates a one-dot graph effect as you need.

    I suppose you realize you could start with a window comparator made from several op amps. This makes a bar graph, however this method turns on several indicators at a time. So you also realize you need to add a method to select one and only one indicator.

    XOR circuits made from transistors can be seen at the website below. It may be possible to adapt these to your design.

    http://www.4qdtec.com/dlc.html
    I tried to make something I figured out this circuit. But I couldn't find a way to block lower levels. For example if I have 5 V as in figure, it doesn't go through R3 yes its achieved, but it shouldn't go through R1 as well it should only go through R2. Transisors and other IC's forbidden except only for opamp.

    Click image for larger version. 

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  5. #5
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    Re: How to create a voltage selector circuit

    I thnk a better topology is to feed your voltage to all the comparators in parallel but set a different threshold for each one. The will give you a 'bar graph' output with none, lowest, lowest and middle, lowest, middle and highest outputs on as appropriate. After that you use the logic gates to make the highest indicator operate alone.

    Brian.
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    Re: How to create a voltage selector circuit

    Hi,

    Your circuit:
    We see a lot of "voltages". Some are used as supply, some are used as input signal AND supply. Not knowing the meaning of the "voltages".
    +4 is never used
    +6 is never used

    There are several mistakes/concerns:
    * please tell us what "Ux" is an OPAMP and what is a Comparator. (In case you are unsure, then read threads about the difference between OPAMP and Comaparator)
    * What type of ouput stage are your comparators? OpenDrain or PushPull?
    * +IN of U1 is the same as itīs positive supply. Be sure you use a Rail-to-Rail input opamp/comparator.
    * Cathode sides of D1, D2, D5, D6 are floating. Floating signal voltage is not defined. No input of an analog IC as well as digital IC should be floating.

    What is INPUT, what is OUTPUT and what is your idea behind the circuit?
    What is the input voltage range?
    Do you expect the ouput to be ON/OFF = digital or an analog signal?

    Klaus
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    Re: How to create a voltage selector circuit

    The usual solution, also implemented in LM3915 dot matrix mode is working like below:
    - have comparators for each threshold level
    - have a priority encoder to pass only the output of the most significant comparator

    Priority encoder is essentially a logic function. It can be however implemented in different ways, e.g. a higher level comparator is blocking all lower level comparators by diode network. Review LM3915 datasheet, section Mode Pin Functional Description to get an idea how.



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