led water level indicator

Simple Water Level Indicator

This is one of the simplest water level indicator that can give up to 7 indications – Full, Half and Low water levels in the overhead tank through LED indications. The circuit is simple and uses a single IC and a few components.

The main part of the water level circuit is the 7 channel Darlington array IC ULN2004. Its seven inputs are connected to seven probes to sense the water level and the corresponding outputs are connected to three LEDs through current limiting resistors. A common probe (common) is connected to the positive rail. When this probe gets electrical continuity through water with the other probes the corresponding LEDs light.

Schematic of the Water level Indicator Circuit

led water level indicator

Here is an idea how to connect the 7 segment display.


Assemble the circuit on a common PCB and enclose in a small box. This unit can be kept in a place for easy monitoring. Use brass or chromium plated pins as probes. Connect the probes with the unit using three core shield wire. Probes should be plugged into the tank through the side. The low probes in the lower position, half probes in the middle positions and high ones in two upper position. If the tank is empty, no LEDs will be on. When the water level increases the green LEDs (marked with G) will start to light up according to the H2O level. When the tank becomes full the red LEDs (marked R) will be on. In short, if Green, Yellow and Red LEDs light, tank is full.


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  • vinzer

    I’m very interested in water level sensors.
    And the big problem I have, with most I’ve seen so far, is electrolysis, which I fear this circuit may suffer from too, in any practical application.
    I reckon it’ll work for a while, but depending on the current level, will result in pitting on one probe and plating on another.
    A very small dc current my reduce this to an acceptable level, between the common probe and the various bases, but I don’t think this circuit has one?
    As I see it we’re talking a mA or 2 into each base terminal?
    Or maybe I’m not understanding it?
    If so, please explain..

  • Ulkesh

    I need bath pull indcator project report of it

  • Nischal

    Sir I liked this and wanted to know how it works

  • akeem

    Sir. Could u tell me 7 simple leveling devices, stating how each one is used

  • Krupa Galiya

    In water level indicator..
    buzzer make a sound to much law
    its due to because of battery ????

  • Adam

    Well I’ve made this sensor using ULN2004 year ago, everything just working fine and perfect!
    The only issue that wasn’t resolved is the electrolysis on the water involving the metal probes with its 12VDC current. I was ended up with the water inside the tank turns a bit brownish, of which I would believe the water was just becoming not hygiene and getting polluted somehow.
    It was copper probes used in my 1st trial, then I tried alum probes but still not that convincing.

    With the copper probes possessing DC current, I suspect the reduction and oxidation reaction was occurred separating the ionic fraction of water and end up with the forming of Cu(OH)2 + H2, and of course the water turbidity.

    I would be happy to hear any solution or experience from all of u.

    • Matej

      Hi, I have the same problem. I did this in a big rain water tank (3500l). I used ULN2803 which should be even more sensitive. It all worked fine for a month, but now only two lights out of 10 work. I tested the board and lights and they are working. So the problem must be in the contacts in water. Is it possible that copper oxidated or something like that which increased resistance too much?

  • Jayant

    I am looking for two different items.
    1. Round PCB having inside diameter of 47 mm and outside diameter of 55 mm with 4 LED installed on it as indicators (all one colour) to work on 230 V. Can I get a supplier for it for bulk purchase in Mumbai, India.

    2. I need a circuit to be installed in a blender for
    Controlling speed, Timer 30 seconds interval up to 300 seconds (10 steps), overload protector with warning Buzzer. To work on 230v AC. The buzzer will operate if the load current crosses 2.2 amps, the buzzer will warn the user for 20 seconds, if the user doesn’t stop the blender, the blender motor will stop automatically after 20 seconds. Motor will have 20000 rpm, it’s universal motor, drawing 1.4 amps current on no load and upto 2.2 amps on load. The minimum step less switch speed for motor will be 13000 rpm and maximum will be 20000 rpm.

  • Balaprasad

    Thanks to you…
    Super circuit…
    I need a small help,i need to add a buzzer..
    Please give the detailed circuit..
    I have tried a lot with pin 10 and others but it leads to failure..
    Please help me to connect the buzzer..
    Give the details about,where to connect the positive and negative terminals of a buzzer..

    • Adam

      Use a transistor to amplify, say BC548 will be fine.
      Or alternatively connect the buzzer (+) to Vcc and (-) to ULN 2004 pin 10 or 16 (depends on your high-low sensor arrangement).

  • goood

    sorry to respond late, I want to do this project to measure levels of benzina.its possible?

  • bk rai

    Sir i have made this project but problem is that when the any senses comes to water contact then corresponding led and some other led also glow with this sensors so sir pl. guide me what is the problem behind this pl. give solution for complete the project. thanks

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