Numeric water level indicator- liquid level sensor circuit diagram with 7 segment display – Engineering project

Water level indicator circuit or liquid level sensor displays the current level of water in any water tank reservoir. Here we use a simple real time encoding circuit with 7 segment display. It can also be used as a water level meter or water level detector. Combining this project with our previous post ‘Automatic water tank level controller’ will give a complete automated control system for home and industries. This water level sensor consist of 8 to 3 encoder (74148- 8 line to 3 line priority encoder) with some water sensor arrangement. The encoded level is displayed on a 7 segment digital display. This circuit uses one ‘Hex display’, it does’t require driver IC to encode. It makes the implementation simple. You can use ‘7 segment display’ with appropriate driver IC 7447.

Circuit Diagram

Components required

  1. Power supply
  2. Resistors (10kΩ x8, 100Ω x3)
  3. IC 74148
  4. IC 7404 NOT gate x3
  5. Hex display

Working of the circuit

  • Water level in the tank or any reservoir is sensed using simple pull up resistor arrangement.
  • Here we define 7 levels in the reservoir. The sensed values are connected to an encoder circuit. The encoder circuit consist of a 74148 IC, which is a 8 line to 3 line encoder.
  • A connection from ground is dipped in water reservoier. When water level rises, the ground comes in contact with the particular pin of encoder input.
  • Without the ground contact, the encoder input is Vcc through the pull up resistors.
  • See the simulation window shown below. Here switch ON  indicates water touching the point A.
  • While water touches the point A, D1 of encoder IC=0, so the input patern becomes 1111110 which is encoded to 110 binary value.
  • The inverted output become 001 using not gate. Thus for each and every level the encoder produces corresponding binary digits.
  • Next section is the ‘HEX Display’ which is a special type of 7 segment display. It is easier to use than the regular seven-segment display because it is already decoded. Each hexadecimal digit is displayed when its 4 bit binary equivalent is received as input, as shown in the truth table below.
  • If it is difficulty to get a ‘HEX Display’ you can use ordinary 7 segment display with decoder driver IC 7447. Hence the encoded values are displayed. This circuit will be really helpful for your project.

Circuit using 7447 driver IC

(Click on the image for enlarged view)
You can neglect the 4th input (D) of 7447 because we are using this circuit to code up to 7 level, that is  upto binary 111. Hence there is no need of the 4th input of 7447.
(Circuit using 7447 is posted as per the request from one of our readers Mr. Nagarajan M)

Truth table

Simulation of this project

Click on the image for enlarged view of animation

Components pin outs

74 thoughts on “Numeric water level indicator- liquid level sensor circuit diagram with 7 segment display – Engineering project

  1. I have tried this project in breadboard but its not working, if the inputs of IC 74148 is connected directly to negative supply it works, but if it is connected to negative supply through wires immersed in water it doesn't.

    any suggestion sir?

      • I think I have the same problem. I make a water level indicator and controller on a breadboard using 74LS148 and other ICs to control the relay. The circuit supply is a breadboard power supply modul with output current <700 mA. when I try to connect the "sensor" wires through the water, it doesn't work but when I connect it directly to the ground grid, it works properly. Even when I use transistors (and darlington arrangements) still it doesn't work. I think I should tray to use a power supply with larger current capacity. Hopefully it will work properly. Thank you

  2. can i use AA batteries to give power supply?
    if yes then what about the required voltage and current?(how many batteries?)

  3. hello sir,
    i need to know about the power supply. Can i give 3×1.5 volts AA batteries for this circuit?
    please give me the reply…

  4. After several years again I have returned and given interest in electronics projects. Thanks to the suppliers of such simple projects.

    • Hi Anil,
      Due to the large volume of comments we are receiving we can’t help you for this pin configuration, sorry.
      Please search for data sheet of IC 74148, where you can find all details

  5. Greetings to you all,
    I’m a student who’s been working on this project. My project supervisor wants a vivid “Design/Circuit Calculations” on this project i.e “why did I use this resistor, transistor ratings and not another; how did I come about the specific ratings; why this particular ICs…”
    Pls, I seriously need them in 2 days time!
    My Email is:
    Thanks in advance.

    • Hi Jackson Imoh,
      Really sorry for the delayed reply. I know it is too late to followup you, but considering to my situation I was too busy with last 2 weeks and did,t get time to reply the comments. Now only I saw your comment..

      Even though let me explain the design aspects. First of all this is absolutely a Digital Circuit! We are manipulating the switching of components. The 1st section is Pull-up resistive switching part, which senses the water presence. For this resistive network there is no design rules! you may use 1K, 10K or even more, the reason is that the Resistance offered by the water must be less then the Pull-up resistor in order to switch accurately.
      This is the only analog section in the circuit, rest everything is purely based on digital switching that we explained in the post.

      Once again I beg your pardon for the late response. I know the situation and timing of an Engineering student, Please don’t feel bad to us. Keep visiting
      For any further assistance we glad to receive your comments.

  6. using ic 7447 the circuit is not working when grd is immersed in water,
    but circuit is responding when directly connected to -ve termial
    can you provide me solution for this.

  7. Sir can I use a 9V battery source instead of a 5V one?
    Actually directly 5V source is not available so I have to use a regulator.
    Please suggest

      • Actually what is happening that the circuit is not working.
        I figured out the problem that since here the ground is actually the negative terminals of the battery, a wire connected from the negative terminals has to be immersed in water. Otherwise it is not working.
        I am trying to make the circuit with as much less components as possible. I have read the ratings of my 74148 and 7447 , max voltage is given 6V. So will it still damage the chips?

  8. Could you tell me how to combine your automatic water tank lever controller with this project?
    What exactly I have to change in the circuit that it will be working properly?
    I have many problems with combinig this two projects and I would be very grateful if you help me.

  9. Sir,
    I made this project but it is not working with wire immersed in water. With salt water it does.
    For the 5V supply I have used a lm7805 voltage regulator. Any suggestions?

  10. And sir there are a list of hex displays available in the market.
    Can you please suggest what is the specific number of this particular hex display?

  11. Hi,
    I tried with this circuit,i have used ic 74148 and ic 7447 and also an 7 segment hex display ,the reading are quite confusing,
    its showing out put different the out put are of 0 intial reading it showing null value and so on ,but it showing different readings ,gs eo is conneted to…and LT BI/RBO RBI they are connnected to where…please explain these..

    • Seems that the guy left us…..I have the same questions, Eagle is saying that I didn’t connect that gates….so probably will work as well.
      I started after more than 12 years of inactivity to make PCB’s again so I have to catch up a lot….

  12. Hi,

    Can someone please add the practical circuit scheme here?
    It would be helpful to avoid loosing time thinking the routing…. 🙂


  13. Hi again,

    Sorry for so many postings but seems that something is wrong with the above scheme….
    Meaning, I have made the circuit but there are some issues with it:
    – it doesn’t show the “0” value
    – it shows different “numbers” if I can call them numbers

    Any help from you would be appreciated. I tried as well with a lower resistance for D0 with no success.
    I also tried with no resistance to connect D0 directly to ground, same issues.

    I made a small movie to show what I mean,
    Please see the below link.

    Thanks again for any help.

  14. plz tell me about power supply of water level indicator 74148N and ic7404 witha all detail of power supply… how can i formed a power supply for this circuit and give me also detai ovf power supply

    • Hi Vivek,

      I used a 12V power source for led strips combined with a voltage regulator bought from ebay (in fact both of them are from ebay).

      With a reasonable price you can buy both of them.

      Beside this, you can use some connectors which will allow you to connect only when you want the above circuit.

      BTW, the above circuit is not entirely correct. The pin No.6 from 7447 must be connected to ground.

      Even so you will still have to improve something because is now counting from 7 to 0 when immersed in water

  15. Hi to all still interested about this circuit.
    I have managed to make it work with a 7404 circuit.
    So, if you want to correct circuit please contact me at

    BTW, I can give eagle file for the circuits, I have made 2 circuits (with PCB), one with network resistor and one with single resistors. The only problem is that the circuit is functioning only with salted water.

    I do have a 2 Ah source but is not working without salted water, is showing only 0.

    A link with the movie for proof.

  16. hey im makin dis project for my dld course but aftr i bought the components im not sure whether i have a hex display which can be used directly without ic driver or i hav a 7 segment display..kindly help me how to distinguish between them it has 10 pins and i dont knw pin configuration of it..hope to recieve ur guidance m

  17. Dear Khaleel,

    Good to see your hard work and helping students like me, can get lots of educational benefits from your ideas, May Allah Bless you for all of these efforts.

    I have a humble request it could be taken as generic thoughts, however; I need to know the ampere rating of all the components required to build the above circuit, and I am sure all the fellows will love to see if in all of your posting of REQUIRED COMPONENTS will reflect the watt/ ampere ratings to be used in the given circuit diagrams.

    Thank you for your understandings and help.

    Best regards,

  18. our society is having a overhead water tank with 3 phase motor to fill manually. I want a circuit to fill automatically for 3 phase motor …can u help with a circuit?

  19. Sir I cant found DCD HEX display in my town and I have to submit my project I try LED display with decoder but its not working. what to do ? plz help me..

  20. Hello sir,may I ask how can I add the LED diode for this case?like level 1 will be a diode light up,and level 7 have 7 diode light up,thank you sir!u reply is very helpful to us 🙂

  21. Can anyone tell how to simulate this circuit in multisim
    I cannot find water tank in multisim.If not possible with multisim pls suggest another simulation software

  22. One question for some disputers who say only salt water. One importatn thig is to have groud wire put in the water. also on nics video is working only with salt water. did he try to groud the water? cause the original circuit have grounded water tank and that is sure importatnt i think is should be from metal and grounded or some groud wire put in to the tank.

  23. am trying to do the circuit using 7447 ic but when i test the circuit am not getting no response the seven segment stays the same no matter what level is at can you please help me to determine the problem. thank you

  24. Hey guys, I just found this discussion. I’ve got an aeroponics greenhouse using 24vac to control sprinkler valves to regulate water/nutrient distribution. Since this is Louisiana, I have (3) 280 gallon tanks buried to help keep the water cool enough to reduce root rot. Even though 95% of the water recirculates, I still need to keep an eye on the level and was looking to use this circuit. (Though with the flood we experienced last week, I can’t even get to it to test, so I’m doing arm chair engineering right now). Due to electrolysis concerns with dc, is there a way to leverage the 24vac supply and modify this circuit? If not, I can always build it dc. Thanks for any help

  25. Hi sir, Rahul Negi, I am making this project , I use ic SN74LS148N ,7447 ic and seven segement display ( common cathode ),
    But when I give power supply seven segement display all segement are already glow and ground wire connect all seven wire , they are not work , what I do, plzz kindly help me sir

  26. im new person to do project, so to mount on pcb i dont know how to mount on pcb board, so help me in more brief description i be able to complete my project, ic mounting is a difficult task

  27. Hi sir I have made numeric water level indicator using ur guidelines but it’s not working I gave 5volt by a adapter of mobile charger using a PCB and by using etching soln drawn circuit diagram but led i s not indicating any number

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