Help -Water hardness analysis circuit

Discussion in 'Homework Help' started by roonie, Sep 17, 2008.

  1. roonie

    Thread Starter New Member

    Sep 17, 2008
    Guys my friends and i have did a project on testing the quality of water..Now the thing is we have bought the project from one shop...I just want to know how the circuit works
    It actually glows the green LED light when pure mineral water is detected and glows red Light with a buzz sound when it is salty...
    This is all i know about the project ...Am not a expert in electronics and circuits i have just joined engineering ...
    Am posting the circuit diagram and am not sure whether is totally correct because one of my senior drawn it by seeing the project..We have used IC LM339
    And am a newbie to the forum hope you guys reply soon...
  2. Nabla


    May 7, 2008
    At first sight, it looks right to me. You have two probes, and two comparators lighting the LED's when the resistance between the probes is above/below a certain level, and presumably the variable resistor is to calibrate the intrument. Also You'd have to have the probes a fixed distance apart, so the resistivity of the sloution is the only variable.

    As for the details of resistor values, and even connections, I'm not sure.
  3. beenthere

    Retired Moderator

    Apr 20, 2004
    It's way too small for me to make out. If the above is correct, then it's a conductivity meter.
  4. roonie

    Thread Starter New Member

    Sep 17, 2008
    Thanks but if you would have explained a bit more clear it woud be helpful..i.e how the current passes thro the circuit wen it is kept with salt water and how does it act as a switch...
    is pure water has higher resistance than the salt water? works on that principal not much clear abt the vol drops takes place n al
  5. scubasteve_911

    Senior Member

    Dec 27, 2007
    The circuit exploits the fact that water conductivity changes when solids are introduced that create free ions. You can read about this phenomena here

    The resources alludes to the necessity of a temperature calibration and to be able to select/detect a media.