LED Water Level Indicator.

Discussion in 'The Projects Forum' started by nath69uk, Jan 28, 2011.

  1. nath69uk

    Thread Starter New Member

    Jan 28, 2011
    Hi Guys & Girls,

    1st post so go easy on me. :D

    Im wanting to make a LED level indicator, so once I press a button it shows me how much water is in a tank.

    The power supply needs to be 12v.

    I was thinking of taking a straight 12v+ feed from the supply and placing that at the bottom of the tank with a button halfway along the wire. I would then solder 10 leds along the same 12v+ feed, then cut different lengths of wire and attatch them to the - side of the leds. When the button is pressed then the circuit is made and the relevent leds light up.

    Im sure I'll probably need resistors and what not so thats why I'm here so someone can hopefully point me in the right direction.

  2. nath69uk

    Thread Starter New Member

    Jan 28, 2011
    xpod likes this.
  3. nath69uk

    Thread Starter New Member

    Jan 28, 2011
    Any plans?
  4. bertus


    Apr 5, 2008
  5. Adjuster

    Well-Known Member

    Dec 26, 2010
    Your circuit is not correct. The LEDs and the electrodes would need to be in series, not in parallel - do you understand the difference?

    More importantly, you show LEDs connected directly to a 12V supply with no series resistor. This is not safe, the LEDs would burn out.

    A practical circuit would also need to use an amplifying switch device, as the current available from electrodes in clean water would be quite small. If you do a Google search using the phrase "water level alarm" you should get some ideas. There seem to be several suggestions for using an analogue switch IC - not something I have actually tried but it looks as if it might work.

  6. hgmjr


    Jan 28, 2005
  7. wayneh


    Sep 9, 2010
    Your circuit needs changes. First, the direct grey connections to the LEDs need to be removed and replaced by a line into the liquid. In addition to blowing out the LEDs, those direct-to-LED wires would make the leg touching the liquid irrelevant.

    Next, you need to realize that for this type of circuit to work, your fluid must conduct all the electricity used to light the LEDs. If the fluid is clean water, it won't work. If it's brine or other highly conductive liquid, you have a chance. The amount of current will depend on surface area of your conductors, distance between them, how corroded or scaled they are, and the liquid's conductivity. LEDs are sensitive to current; too little and they will be darl or dim, too much and they're gone.

    A better approach, that still relies on touching the liquid, would be to detect a small amount of current and then amplify that to exactly what the LED needs. This would require an op-amp circuit, but would free you from most of the worries about clean conductors and so on, and would protect your LEDs. It might even work for detecting clean water.

    More advance techniques of level measurement don't touch the fluid, or at least don't touch it electrically. The level indicator in every gas tank works by using a float to change a variable resistor.