This is the circuit diagram of a simple corrosion free water level indicator for home and industries. In fact, the level of any conductive non-corrosive liquids can be measured using this circuit. The circuit is based on 5 transistor switches. Each transistor is switched on to drive the corresponding LED when its base is supplied with current through the water through the electrode probes.

One electrode probe is (F) with 6V AC is placed at the bottom of the tank. Other probes are placed step by step above the bottom probe. When water is rising the base of each transistor gets electrical connection to 6V  AC through water and the corresponding probe. This, in turn, makes the transistors conduct to glow LED and indicate the level of water. The ends of probes of the water tank level indicator are connected to corresponding points in the circuit as shown in circuit diagram.

Insulated Aluminum wires with end insulation removed will do for the probe. Arrange the probes in order on a PVC pipe according to the depth and immerse it in the tank. AC voltage is used to prevent electrolysis at the probes. So this setup will last really long. I guarantee at least a 2 years of maintenance-free operation. That’s what I got and is still going.


Transistor (T1 to T5)BC 548 or 2N2222
Resistors (R1 to R5)2.2K 1/4 W
Resistors (R6 to R10)22K 1/4 W
LED's (D1 to D5)Color of your choice


Use a transformer with 6V 500 mA output for power supply. Do not use a rectifier! We need pure AC. Use good quality insulated Aluminum wire for probes. If Aluminum wires are not available try Steel or Tin. Copper is the worst. Try the circuit first on a breadboard and if not working properly, make adjustments with the resistance values. This is often needed because the conductivity of water changes slightly from place to place. The calibration for simple water level indicator levels will vary according to the medium of liquid whose level is to be calculated.  The type number of the transistors used here are not critical and any small signal NPN transistor will do the job. Few other suitable type numbers are BC546, BC107, PN2222, BC337, BF494, ZTX300, BEL187 etc. The circuit can be enclosed in a plastic box with holes for revealing the LEDs.

Water Level Indicator Circuit Diagram and Sensor Arrangement.

Water Level Indicator Circuit diagram
Water Level Indicator

This is the most basic form of water level indicator used for measurement. If you need a fully automatic water level controller circuit then try this circuit  Water level controller. The circuit is fully based primarily on transistors. The sensing section is somewhat similar to this circuit but there is additional circuitry for switching the pump ON when the water level falls below a set level and the pump will be switched OFF when the tank is full. A few transistors, one 555IC and an electromagnetic relay are used for realizing the control section. The circuit is very simple cost-effective, reliable and many guys have successfully assembled it. I am also working on a float type water level indicator/controller using the float type fuel gauge mechanism used in motorcycles. The level sensor section is finished and now I am working on the control circuitry. I will add the circuit here as soon as it is finished

Note:- We have recently developed a much better and fully functional Water Level Controller circuit using 8051 Microcontroller. This water level controller monitors the level of the overhead tank and automatically switches on the water pump whenever the level goes below a preset limit. You may see the circuit and try it.



  1. David Long

    I think this circuit does exactly what I require… well almost.
    I’m looking to stop a pump activating when my water butt is empty. At the same time it would be useful to see how full the tank is ( using the LED approach)

    How would I modify the board to switch off a 240 supply. My pump is attached to a lightwaveRF plug so would have to put something before the plug to cut power.

    The aim of the game is stop my pump running when the tank is empty.

  2. chaitanya takalikar

    if we wanna implement this in proteus, how can we perform this if we dont have water tank in proteus?

  3. plz…….send me the source code or program by mail plz i want to implement in my home

    • I have constructed the above circuit, but prior to the probe diped in the tank, even without probe, the led lights up and i used buzzer in one transistor that is humming, I hope it takes the stray a/c signals, and the voltage across led is only 0.75V

      Please mail me to cut down induction,and to improve brightness of led. ( I use 1.5V LED)

  4. Hello.
    Is there a sensor that can be used in saltwater for detect water levels that will not be effected by electrolysis?

    • Why not use a PIC to give High frequency square wave as transmitter and receive it using same PIC(with other input) through water and detect water it won’t corrode as high frequency!

      • @MVA Because The Above Mentioned Circuit Is Simpler And It Teaches Us Transistor Theory Which Came Before PIC;S . And No Programming is Necessary!!!! Great Circuit whoever Posted This,,,Many Thanks!!!!!

  5. nethi kiran

    water is insulator. so how does the current passes in our circuit.please reply

  6. pls show me a finished version of water level indicator

  7. Nayana p

    I have decided to fabricate water level indicator so plz help me to get its circuit and dng procedure to design it
    thanks in advance

  8. INSTEAD of ac supply which supply can we use?

  9. i want an alarm for the gold shop and for the house too. The alarm should be given for the mobile too.see this tecqnology is there as this is very much needed for me

  10. sangeetha.r

    The project was nice i have decided to make it myself…, please send me the essential informations for preparing it including the components and how to design it…,

  11. i liked this project.please give me some information about this

  12. Can I make this into a ten level led level indicator instead of the present five? (of course that many sensor wires will be going into the overhead tank.) Please confirm. Do I need to do any further modifications? Same voltage?

    • yes by adding more transistors along with biasing resistors you can get more out puts with same voltages
      but with good ampare source

  13. Prajjwal Bisht

    plz… somebody help me… i have an electronics project to submit by the end of this year 2014… plz suggest me a project that can be made easily and would fetch me full marks…

  14. please can you show the picture of the circuit. I am in class 10th and not able to make it. If you could kindly send a picture it will help me

  15. Santosh Mahto

    awesome project especially for the begineers..!!!

  16. how can make 3 level sensor with two automatic turning on/off the two pimps. If the water level is below the first level the two pumps are on, when the water is above L1 the water pump2 stops, and the pump1 will stop after reaching the level 3. using arduino

  17. Laxmi m h

    sir, i am interested in this project so can u please sent me the circuit diagram and its working.
    thank you.


  19. sir, i am interested in this project so cant u please sent me the circuit diagram and its working.
    thank you.

  20. Hi! It is one of my favorite projects. It is very interesting and has been proposed by many experts.

  21. hi me too finished ah water level indicaitor.. But i have a doubt that if 12v DC supply given to the water does it affects, since always the probe will be inside the tank all the time with the supply.. Does this setup affects the user since water flowing carries 12v DC supply

    • Seetharaman

      Hi Karthik this circuit uses a low voltage AC to the probes hence it will not give any shock. since AC is used the probes will not get eaten away. Instead If DC supply is used the probes will be eaten away very fast due electrolysis action.

  22. janardhan

    Dear sir, i made the above shown circuit and tested and working fine. But there is your reply for ahmed, please can you show/explain me how this will be connected in the above circuit. and also please show alarm connection for full tank indication in the above circuit. Thanking u sir, janardhan, tirupati, AP.

    December 19, 2011 at 5:42 pm

    Hi Ahmed connect new added transistor ‘T0′ base to collector of T1. connect RED LED from collector T0 via 220ohms 1/4 watt resistance to 6VAC line and emitter of T0 to GND(common).

  23. vivek dnyanoba bidgar

    I required more details about the water level controller indicator,because i am a new student of electronics. For only practices I required more details.I hopes you provides it on my mail.

    vivek bidgar

  24. Joao Alexandre

    You can drive a relay with this circuit ?

  25. Hello, is it necessary to use 6 V AC or is it ok with DC?
    I also want to install a buzzer at the final level, please send the modified circuit.
    i want to submit this circuit for my project, i am a first year B.E. student

    • Seetharaman

      Hi Amith 6 volt AC is essential because to avoid electrolysis in the water due to salts contamination. (with DC your level sensor probes will be eaten away in just 10 to 15 days of operation due electrolysis process).


  27. somnath sarkar

    My building ht. is about 45 mtrs. Is it applicable for the same or any modification is require? Please suggest.

  28. Ganapathi

    please tell me about the operation of this liquid level indicator.
    I want to this kindly inform me .

  29. Hello all,

    This is the best and simplest circuit I have seen in web. I made this and its working very good. I have seen lots of questions and doubts here.So I posted in my blog few pictures and high level guidance. Please post comments if you have any questions.

    • Please guide me a bit…. i m gonna make it, tell about circuit diagram etc

  30. sir

    i require automatic water level sensor.with ic555.and 547 transisters.up-down level indicator.through rely on-off,for my house water tank purpose.

    thanking you sir
    yours truly

  31. Pinjara jishan

    Respected sir, i like your project water indicator. Plz more details this project and ckt diagram and it’s working. So plz reply sir.


    give me some project ideas on minor project on communication.i am a student of 7th sem
    frm electronic n telecomunication.branch.
    plz help me
    mail me ~

  33. Jitendra mattlia

    I have build this using IC 91214 and 8870. Using DTMF, i used only 2 wire from roof top to ground floor. It displayes water level on seven segment digital display. Also contact less sensor like reed switch is used for sensing with magnet mount on thermocoal.
    Circuit is working well for last 5 years.

  34. HARIKA
    JANUARY 23,2013
    iAm interested in simple water level indicator i want to do this please circuit diagram and its operation.and also explain the how to work & use the resistors,transistors ,led.where it place the alum minim probs.

  35. sir,
    i am intrested in water level indicator i want to do this project so please send me the circuit dig and its opration
    thank you

    • Jitendra mattlia

      Kindly send ur email address, so that i can send u circuit diagram and full detail and other helping tips.

    • just get transistor of value c1383, then check on google about the biasing of the said transistor as a switch, then complete this circuit , its quite easy

      • or you can use any NPN transistor its very very easy priyanka if you need more help contact me at my email

  36. sir, we are facing a problem in the circuit.our all leds glow, even if the wires are not kept in water. we are using thin copper wires.. is it because of copper wires??

  37. Thanks for the circuit. It works perfect and i have connected buzzer too. However when the probes are immersed in water the voltage gets lower which result in LED glowing dim and buzzer sounding low.

    Please let me know what needs to be done in this circuit?

    • victor lab

      hey Eddie, can you pls give me your findings when you assembled the components?

  38. Hi,

    Thanks for the circuit and it is working fine and i have attached the buzzer too. when it is immersed in water the LED glows very dim and buzzer sound is very slow. What should i do to increase the LED glow and buzzer sound. It is sounding fine when the wire touch each other but not when immersed in water.

    Do i need to change resistor value or increase the 6V AC. Please suggest what needs to be done at the earliest.

  39. Sir,
    does we can use it as heavy water level indicator..
    i lyk dis project..
    am going to d dis practically and if possible i may modify it…..

  40. without transistors we can implement the logic s(n+1)=s'(n)b’+s(n)a’
    using 7400 7408 7432 7400
    remaining same i.e water sensor same as above
    a high level and b low level s(n+1)is fed to relay directly and we have succeeded in that.circuit is working
    any suggestions are accepted

  41. without transistors we can implement the logic s(n+1)=s'(n)b’+s(n)a’
    using 7400 7408 7432 7400
    remaining same i.e water sensor same as above
    a high level and b low level s(n+1)is fed to relay directly and we have succeeded in that.circuit is working


    Did you can make easy electronics circuits for tenth and below

  43. I am doing this circuit for my project but as far I am seeing need to do some calculations therefore form what i am seeing here on this circuit the transistor configuration is a fixed bias configuration but i have a bit of a problem when i am calculating Vce i am getting a negative value why is that Vce is always positve ….my question is why Vce is negative using the resistor values given in this circuit

  44. vaisakh v m

    i like this project sir. can i get the detailed project report for this water level indicator. i like to do this project for my 5th semester. pl send it to my mail as fast as possible

  45. sir,i would like to do this water level indicator project..
    will u plz send me the ckt diagram and its working details to my mail…am intersted to do this project.
    plz help me sir

    • i too have a circuit similar to this and very easy than this i’ll mail u if u want that

      • please paste ur ckt which is easy than the above mentioned ckt……awaitnig ur reply..

      • Sir,
        I have intrest to do this ld like to do this water level indicator project..
        so,will u plz send me the ckt diagram and its working details to my mail…
        plz help me sir.

      • hello,
        i would like to have the easy project on water level indicator which u have……
        can u plz send it to my mail……

  46. abdullahi

    sir ,iam a final year student,my project is liquid level control and indicator using 16f877microcontroller, i need the cct diagm,and detail explaination.

  47. The distance from the tank to the circuit is about 60 meters, Will the design work?
    Also can it be used for chemical tanks using a stainless steel probe? such as Acid, Chlorine.
    finally can i add the number of LED to about 10 for a large water tank about 120m3?

  48. Has anyone built this circuit and was successful with the operation would like to know thank you

    • Me.
      I just make the diagram, with no changes, and works fine.

  49. Hello Mr. Seetharaman

    Well I started off with my circuit with 12V / 1A transformer. I tried the circuit with 12V AC to probe F and probe E to the base of a BC548 transistor. In place of R5, I connected a 12V buzzer. The result was that there is a constant mild sound from the buzzer and no variation when probe E is inside or outside water. I checked the voltage at location of R5 (where buzzer is connected) and it constantly 10V irrespective of whether E is immersed in water or not. Kindly help.


    • Seetharaman

      Hi Paul just replacing transformer and a buzzer will not do. since all the voltages are either rms ac or rectified dc, hence you cannot measure or operate. the circuit to fully re designed with ac and dc operation. ac for the sensor and dc for operating a relay or a semiconductor alarm.

      • Dear Mr. Seetharaman

        Thanks for the response; Can you please provide the circuit for the requirement?

        Thanks in advance…

  50. Hi i would to know if there is any way i can use this circuit and incorporate it with a another like to sound an alarm using the 555 timer for low and high level basically the circuit i want to design is a water level indicator an alarm circuit any ideas ..

  51. Hello Mr. Seetharaman

    I have a 230 / 12-0-12 V, 1A transformer. Can I use it in this circuit? Is it harmful to create electric shock in water? If in that case I shall go for 6V. The reason for opting 1Amp o/p Xmer is that the tank is atleast 30meters from the circuit location. Will 500mA satisfy the length?

    Nextly I’m planning to use only probes E and F, where output of T5 should power a piezobuzzer. Please suggest the circuit amendments to suit the buzzer instead of LED.

    Many thanks in advance.

    • Seetharaman

      Hi Paul use the recommnded transformer for positive results with different transformers you have change all resistance values suitably.

  52. Ravi Sharma

    Can u do it with logic gates only, no transistors, just one simple circuit, not too complicated like this one.
    Thank You.

  53. Ravi Sharma

    This is a great post, i think you can do the same thing with digital gates (no transistors) actually I need this circuit for my project. I hope you can post it ASAP. Thank You.

  54. Goods at auction

    You are actually a good webmaster. The site loading pace is incredible. It sort of feels that you are doing any distinctive trick. Moreover, The contents are masterpiece. you’ve performed a wonderful activity in this matter!

  55. Gaurav patil

    Dear sir i want all procedure of how to done water level project with ckt & all solution

  56. hi sir.. can i also get a copy of this project?? could you please sent it on my mail with full description i like to make it as our project. thanks.

  57. i like this project sir. can i get the detailed project report for this water level indicator. i like to do this project. pl send it to my mail

  58. Vishwanath

    Dear Seetharaman,

    * I have done my own mechanical device to indicate “water tank high level” as well as “no flow of water to tank” with mobile charger supply 5 v D.C. using piezo beeper alarm. Works very good, but rugged construction.
    Your above circuit needs a bunch of wires to run about 15 meter length, of course we get alarm at any level of the tank.
    * I wanted an electronic device to be done, which works with linear indication of tank level (i.e. 0 to 100%) and it operates the pump at low level and high level. Another circuit in parallel is needed to stop the pump when pump runs dry more than a minute (i.e. if source water tank is empty)
    Please help me to get the solution. Anticipating your earliest reply to my E mail.
    Thanking you
    Vishwanath Udupa

  59. Seetharaman

    Hi Manish Burning of transformer is very rare with good quality ones. You can include a 250mA fuse in the primary to protect it. If the wire is too long it may pickup stray AC signals and give falls triggering. You can use a 0.1uF ceramic disc capacitor between base and ground of each transistor.
    Hi Joseph kindly check the connection to common probe F from 6 Volt AC, check collector base and emitter connection of transistors. Each manufacurer has his own configuration in labling the pins. Finally check the LED polarity. short lead should go to GND and long lead should go to emitter.

  60. anyi joseph

    please i’ve tried to build the circuit,with everything in place yet its not working properly. the LED are not showing any indication when the probes are properly place. please what may be the possible cause of this. please i need your answer urgently

  61. Manish Sharma

    Hello Sir,

    is it not dangerous to take direct 6 volts of transformer to into tank is there not any risk of power shock if transformer burn out .
    Is there any impact on heperformance of transformer if the legnth of wire is about 80 metres from transformer output to tank.

  62. Manissh Sharma

    Hello Seetharaman,

    I have make this level indicator using 547 transistor and 12volt transformer and it working fine i have two questions plz answer them .
    1) we are taking direct wire of transformer out put to tank what if transformer burn is there any risk of Shock if transformer burn out.
    2)Does the Length of wire from water level indicator to the the tranformer have any affect on the performance of transformer plz reply to my question thanks

  63. Seetharaman

    Hi Azad why 6 volt AC should be lethal and 6 volt DC is safe? I dont under stand. 6 Volt AC is good enough nothing will happen. The electrodes also will not get corroded due to electrolysis, which will happen with DC. This is a well thought out design.

  64. hi,

    i need a water level detector circuit. i seen above circuit but the fault is that you are working on AC6V which could be dangerous. i don’t think that we should allow ac current in water tank.

    could you advice some thing save or based on dc current or sensor base. besides, i am also working on DC current but i got resist of problem of water. since water resisting so dc current unable to flow easily that’s why circuit is useless for filled tank.

    hope you would send me better solution.

  65. Seetharaman

    Hi Friends for full level alarm use probe ‘E’ In place of R5 connect an electronic bleeper which can work from 2 to 12 volts. put a link in place of LED D5.

  66. LED only glow in DC mode. But u say AC 6v Transformer without Rectifier.. Then how it glow…
    And when tank is to be full how can i get notify by sound. is there any buzzer to install..
    Pls reply

  67. When tank is full nodify in sound mode.
    how can i install

  68. hello
    I want to install a buzzer at full level
    how could i install it????
    plz reply

  69. sai kiran

    i did not get the use of resistor in our circuit

  70. Seetharaman

    Hi Sai you can try, with tank water conduction with the low voltage a minute current alone can flow through the LED and it will glow very dim even in total darkness you will find it difficult to see the glow, hence the current is amplified with a transistor and fed to LED such that you can view the glow during day light.

    • and how exactly will the current be amplified by the transistor?

  71. I want to know the use transistor and resistor in this circuit.
    generally,from the supply,negative terminal let us connect to LED directly,
    the positive terminal place in tank.from the tank connect to LED.since water is conductor the LED will glow.why cannt we use this simple method.why these resistors and transistors?

  72. Dear Friends

    I have a doubt, instead of four stages can I have only one stage, i.e. the last one (stage E)? Also what changes I have to make to replace the LED with a 12V buzzer?

    Any help shall be greatly useful. Thanks in advance.

  73. dear sir,
    please send me ckt diagram of water level indicator with full description

  74. i know this is a simple & usefull ckt,i got this topic for miniproject……if i get any pblm i wl contact u again..

  75. seetharaman

    Hi Bob with DC the probes will act as electrodes and start electrolysis action, by which the electrodes will start getting corroded soon and the function will get affected. To avoid this AC is used, hence no electrolysis and the probes will be cleaner for a longer duration.

  76. HI!

    I have a problem!

    I replaced the transistors with a darlington array (uln2003) and it becomes VERY hot with 9VAC ! It’S stays cool with 9vDC ….Why?

    Also, I don’t understand why there can be AC current at the probes
    because the LEDs don’t let the reverse current pass to have the negative AC wave !!!

    Thanks for your help!

  77. vijayaraj

    i have already installing automatic waterlevrl swtichs I want some advanced circuits to prvent motor burning



    Need an electronic diagram with value of electronic parts for measuring water level in wells /tube-wells.
    when the simple 2-wire probe touches water level in wells the LED & Buzzer
    should be ON, operated with 3 VDC.
    Thanks and regards.

  79. adinarayanan

    hai i got parts as per your list. but , your picture doesn’t show which direction to fix it. the resister position better you give me original photo in this page, thanks

  80. i want circuit diagram of water level indicator in this LCD except than LED……

  81. ramesh kumar

    this is a very simple structure of water level indicator.
    i like it but i want to know more about water level indicator. please reply me.

  82. Seetharaman

    Hi Ahmed connect new added transistor ‘T0’ base to collector of T1. connect RED LED from collector T0 via 220ohms 1/4 watt resistance to 6VAC line and emitter of T0 to GND(common).

  83. Dear Seetharaman,

    I would like to add a stage before T1 , another transistor (T0) with red LED and it is OFF when T1 is ON and vice versa so that the whole circuit works as follows. When the Tank is full, no red light (T0 is off) and when tank is empty only red light is ON.

    I would appreciate the full details for the modifications required with values and how they are connected.

    Thank you

  84. mohit kumar sharma

    this is a very simple structure of water level indicator.
    i like it.
    so thank you very much.

  85. mohit kumar sharma

    this is a very simple structure of water level indicator.
    i like it

  86. barnaprince

    Dear sir
    I want simple water level indicator circuit with LED indication. please reply me..

  87. Dear sir,

    I would like to add a stage before T1 , another transistor (T0) with red LED and it is OFF when T1 is ON and vice versa so that the whole circuit works as follows. When the Tank is full, no red light (T0 is off) and when tank is empty only red light is ON.

    I would appreciate the full details for the modifications required with values and how they are connected.
    Thanks for your prompt reply.

  88. Dear Sir,

    I want to make T1 off when T2 is ON and vice versa so that when the tank is full no red light (T1 OFF) and when tank is empty only red light is on (T1 ON). I would appreciate giving full details of the modifications involved. Thanks in advance for your quick reply.

  89. akash kokate

    sir,i have to control water level so what i do for it? plz reply…………

  90. seetharaman

    Hi Neeraj Connect free end of R6 to R10 to A sensor to E sensors in the tank.

  91. Richard Anderson

    Hi staff,
    I would also like to use these level indicating probes in a dual purpose possibly thermocouples into measuring the water temperature. I am generating hydrogen (the electrolyte is Sodium Hydroxide) using a 12 volt car battery. If possible I would also like to auto fill the 64oz container.

    Any suggestions?


  92. seetharaman

    Hi Sameer you can use 9 volt battery (only the sensing electrodes will get oxidised soon you require frequent cleaning). Connect +of the battery to 6Volt AC point and – of the battery to common ground. To connect an electronic buzzer for high level alarm connect a BC148 transistor base to T5 emitter and emitter to common ground. connect the collector through the electronic buzzer to 9 volt of the battery by observing the polarity on the buzeer.

  93. sir if iam using buzzer to indicate the tank full.what will be the changes……….plzzz sir tell me what to do. i really need ur help.

  94. sir can i use 9v battery insted of 6v if i am using 6v where to connect the conection. one at the 6v indication and other at gnd.plz reply fast wanna submit the project.

  95. bkwassss………………….kuch mzzedaar bnao yaar….

  96. KM Ealachola

    Thank You for the information Mr. SR
    KM Ealachola.

  97. seetharaman

    Hi KM you can use, since they are not screened your routing is very important, if the cable is too long. If you are in doubt use a metal conduit to route and ensure the cable is dressed away from mains cable route.

  98. KM Ealachola

    REMINDER: Hi sir, I am still waiting for Your answer for my question posted by me on 24th June 2011, regarding the connecting wire between the sensor and the circuit.Briefly, my question was as follows: “Can I use a CAT8 ethernet cable to connect the sensors to the circuit?

    “Can I use a CAT8 ethernet cable to connect the sensors to the circuit”

    Read more:
    Under Creative Commons License: Attribution

  99. KM Ealachola

    Dear sir,
    Please ignore my previous mail, since I got answer for that question from previous posts. My water tank is about 13 meter apart from the room where I indented to fit the indicator. I have insulated Aluminium wire of 18 SWG, which I can use to make the probe. Can I use a CAT8 ethernet cable to connect the sensors to the circuit? I hope You will reply me soon as I finished my other works and waiting for your reply to purchase suitable wire to connect the sensors to the circuit.
    Thank U.

  100. seetharaman

    Hi KM you can use 9 volt transformer without any modification.

  101. KM Ealachola

    Dear sir,
    I am very much interested in your Water level indicator and preparing to assemble one soon. I have a lot of step down transformers in my home stay idle. But none of them have an out put of 6V. I have 9 Volt and 12 volt transformers. How can I use a 9V transformer in place of 6v ?. What modification to be done on your circuit to drop the voltage to 6V ?. I am looking forward for your reply,
    Thanking You,
    KM Ealachola.

  102. Seetharaman

    Hi YNJ FC you can use DC, the circuit will work.
    Hi Pritesh please go through my earlier comments on this problem if the connecting wires are too long, etc.

  103. Please, can I use a DC source instead of AC source. This is for a small project,and will not be used for a long time.

    So, changing to DC source will affect the circuit? Will more components be needed?

    Please reply… 🙂

  104. sir i have probblem that led are glowing dim continously. and when water comes to the prob then it glows bright so please give me its solution.

  105. Seetharaman

    Hi Shashank you can use 9 volt, no change is required.

  106. deepak jairath

    1stly thanxz 4 dt u may upload that kind of ckt in site
    sir, my requirement is dt i will make a project which may also mention d automatic control water level ckt at OHSR
    so dt it may give supply 2 public as per requirement

  107. can we use 9v supply aginst 6v…?
    Plz reply…

  108. Seetharaman

    Hi Akhil have connected one of the transformer 6volt AC to F line and other one to common shown as ground. Also ensure F probe is connected to transformer. Check collector, base & emitter of transistor – the lead arrangement differs from manufacturer to manufacturer. Also check the LED polarity. If every thing is ok it should work.

  109. Akhil mathew

    hi i just want to know if its okay to use 4 sensors other than five as given in the diagram..i connectred the sensor to a 6V AC transformer but still nothing works!!!

    awaiting for u r reply

  110. Seetharaman

    Hi Aki you can use input 115 volt instead of 230 volts or you can use a 12 volt to 6 volt step down transformer.

  111. sir thanks for ur reply…!
    i want to ask u something related to voltage if u can suggest plz help,
    sir as in circuit its 6v AC is used but i have DC source of 6v for the same, but i have a 12v transformer so sir can u tell how can i use this 12v AC transformer to reduce it to 6V AC transformer.

  112. Seetharaman

    The cable can pick up stray mains hum and the LEDs can glow dimly. add 0.01 ceramic disc capacitors in parallel with the base and ground of each sensing circuit.

  113. sir,my problem of dim lightening is over when i did with wires connection and when i mounted on pcb it started glowing means very dim without any probe in water so sir y this happening in pcb connection but not in wires connection,
    and too sir i have to mount the circuit in my building basement and water tank is 50m high so as very long wires will be used (5 wires each of 50m) so there will be any problem in doing so or not….plz help…

  114. Seetharaman

    Hi AKI this is due stray pick up check the cable routing/ or cable may be too long picks up stray field.

  115. i made this circuit but when i dip in water it lights up but when there is no water id lso lights up but very dim, so y this happen on remove of water a very dim light glow..
    plz suggest

    waiting for ur reply.

  116. Seetharaman

    Hi Akhil F sensor is connected to 6 volt AC point. when the water level goes below sensor B let the pump start filling the tank. once tank level reaches E level let the pump stop.

  117. Akhil mathew

    HI i just want to know what the F sensor in the diagram is and how can i attach it to a water pumping motor for automatic on or off using a relay……


    Sir, I assembled the above circuit (with only one section out of 5 sections shown in the diagram i.e.R1,D1.T1 and R6).I also attached a buzzer in parallel to Dl. I converted the voltage to D.C. by a rectifier. I reduced the value of R1 to 330 ohms as suggested by Sri Seetharaman (Oct.5,2010). It is working very very fine for the last so many months. I used ordinary electrial wires as probes,but in the last I joined about 1/2 meter of Electric alluminium Service cable wire (available in Electrical shops), after redcing the number of alluminium wire strands from each wire (Red wire and blck wire) to make it thin and both the probes I put inside top protion of Over head tank (please see that there is no shorting between the two probes). Whenever I switch on the Motor to fill up the overhead tank, I also switch on this water level indicator , so that as soon as the water touches both the probes , the LED light along with buzzer sound, will come and we switch off both the switches. Instead a common switch also can be arranged if it facilitates. I am thankful to CIRCUITS TODAY for giving the above circit.

  119. Manmohan Garg

    Thanks a lot for the good work.
    I have made this device with the same specified components and working perfectly well in Haryana (India).
    I have used 12V instead of 6V as LEDs brightness was not good with 6V supply.

  120. Hi, I have one more question that is, in this above circuit NPN transistor is used then please tell me which point is Base, emitter and collector.please reply me soon to complete this circuit. Thanks a lot.

  121. Seetharaman

    Hi Zubair it will be the bottom most, below the minimum level probe.

  122. Thanks for reply sir please tell me where does the F probe connect in the circuit?

  123. Seetharaman

    Hi Zubair kindly connect one lead of the transformer secondary to 6V AC and the other wire to point indicated as GND.
    For probes you can use 1/18 PVC insulated aluminum solid conductor. tip exposed by about 10mm will do. All these 6 probes (wires) are fixed around 15mm plastic conduit with thin plastic rope. size the length of the conduit kept such that it is tight fit in the tank by using bottom and top covering of the tank so that the whole assembly does not move or fall off.

  124. sir please tell me that where i connect the 6 volt main A.C negative point? and where does the F probe connect in the circuit?reply me soon Thanks.

  125. Dear Sir,
    Kindly send me a reply with more details about water electrode probe, please also send me a photograph too.reply me soon. thanks

  126. N Subramanian

    Why my last question is not answered, but 3 or more questions asked after me are replied?

  127. nauman,
    please include your preferred topic. Then maybe we can help you to decide which one are you going to choose.


  128. Seetharaman

    Hi Rougy correct F should be connected directly to 6 volt AC point. The electronics can be around 20feet away, routing of cable is very important.

  129. Rougy Y. Daanaah

    Thanks, Seeth. for the response to my earlier question.
    Pls i have finished connecting all the various components as indicated in the diagram, but i don’t get the response u gave with regards to where to connect the F in the circuit. you said it should be connected to the 6V AC. Is it directly or what?
    Also i will like to know to try out my prototype on a breadboard. Will the circuit be sitting somewhere while the probes lie in the tank?

  130. hi
    respected sir
    I got this ready project
    replay soon

  131. What if we use aluminium wire immersed in water and then connected to transistor using copper wire in between?

  132. Dear Mr.Seetharaman,

    I am an electronics hobbyist (novice) and I lack theory.

    I need few clarifications for “Simple Water Level Indicator”.
    Can I use 4 pair telephone cable for probes and wiring?
    Can I put the probes alone at the tank and have the rest of the circuit at kitchen, beside main on/off switch of the motor at about 30 feet away from the tank?

    What are all the modifications needed to the circuit?

    Thanks & regards,


    • admin

      Can I use 4 pair telephone cable for probes and wiring?
      Ans: YES
      Can I put the probes alone at the tank and have the rest of the circuit at kitchen, beside main on/off switch of the motor at about 30 feet away from the tank? Ans: YES

  133. Sir,
    why transistor using in circuits.can i replace with 2 diodes.

  134. Seetharaman

    Hi Amna The collector resistances limit the current through the LEDs. Say you use a Red LED, it requires 5mA @ 1.7 volt for a fair glow. The supply is 6 volt the VCE sat is say 0.7 volt for 2N2222. total voltage drop required is
    6-(0.7+1.7)=3.6 volts. current is say 5mA (0.005Amps) then the collector resistance required is 3.6 / 5 kilo ohms. say nearby preferred value of 680 ohms. (Vbe is 0.2 volt is for germanium transistors for silicon transistors it is 0.7 volts)

  135. This project is perfect for me as i am just a learner at the moment. Since there are some specifications i have to follow, i wanted to ask u about them, if this circuit (the values of resistances) follow it or not or how to calculate the valus if it doesn’t:
    1. there should be a 0.2 Potential difference between the collector base and emitter base of the pnp bjt used
    2. current should nnt be more than 2 Amps

    I would be grateful if u can help me out in this

  136. hello my friend.
    i have see your scheme and the transistor 2n2222 does he work with AC corrent or not, and does have LED to work with AC corrent. please email me.

  137. Seetharaman

    Hi Lakshmi the leakage path between the vessels might have been sufficient to light up the LED.

  138. v.v.lakshmi

    Dear sir,
    Thank you very much for your kind information.
    I made this project in our college science fair.
    while doing this project I tested the LED by keeping the base terminal in water and keeping the F terminal in another vessel carrying water. Now the LED is glowing.
    please explain me how it is working even by keeping the F terminal in another vessel carrying water.

  139. Seetharaman

    Hi AJ Check with different probe input (swap the inputs of working one)may be input resistance in not low enough for the probe.

  140. Dear sir
    Only my second LED is not glowing even though the transistor,resistor,LED related to that are in working condition, although the current flowing through all the transistor is same. Pls reply fast sir…

  141. Seetharaman

    Hi Roughy The list shown is ok but only R1 to R5 to be reduced to 470 ohms for brighter LED indication. you may use RED for low. yellow for medium level and green for high etc. to have better illumination from all these LEDs R1 to R5 to be reduce as above. Please also refer to the notes given below the article.

  142. rougy daanaah

    Please as part of my final year project, i to build a simple water level indicator. But am not too sure of the components required to build the circuit. Help some help.
    Thank you.

  143. Hi, If i want to connect a buzzer, how can i connect it to the circuit to function well, pls suggest the buzzer too

  144. Seetharaman

    Hi Thomas there is nothing wrong in the circuit working fine for the last more than 6 months with 2N1711 transistors ( which is similar to 2N2222 and that was just on hand). i will send my prototype photos soon.
    Hi Malli You can use any insulated 18 Gauge solid wire any conductive metal. (expose around 10 mm for sensing).

  145. Hi sir
    Should i use only aluminium wire or can i use copper wire sir.

  146. Thomas Mierzwa

    transistor pinouts are correct as installed. 2N2222 has a metal can. Collector is connected to the can. Emitter is indicated as a tab on the can. Something is wrong with your circuit.

  147. Seetharaman

    Hi Thomas Collector to Emitter is OK bur base emitter shorting should remove bias for the transister and it should estiguish. colector base shorting will give forward bias to the transistor hence it should light up brightly. it is happening in opposite way. kindly check the transistor lead out and rewire if necessary’

  148. Thomas Mierzwa

    emitter to base shorted as requested results are the led lights up brightly. emitter to collector led lights up brightly. collector to base led goes out.

  149. Seetharaman

    Hi Thomas it should work as it is with high efficient 5mA LEDs. The When you plug AC and if all LEDs are glowing it is through the leakage path in the base circuit. kinly check up by shorting each transistor base and emitter, if the corresponding LED goes off then it is clear indication of either leakage path or stray induction is resulting in this glow. to eliminate this problem and to suit your type of LED, the above suggestion was given. These are all basic simple circuits may require refinement at times as per the operating conditions.

  150. Thomas Mierzwa

    Is this experimenter’s corner? Because I have $62 U.S. tied up in this so far. For your information the resistivity of water is 820 ohms @ 25C. As soon as I plug in the transformer, ALL LEDs light up, not brightly but they are lit. When I immerse a level probe into the water, the LED it is connected to increases in brightness ever so slightly. I was under the impression that the LED should be out completely until THAT probe’s sensor was under water. What is the function of the capacitor that is in parallel with the collector resistor?

  151. Seetharaman

    Hi harry Reduce R1 to R5 to 330 to 470 ohms to suit your LEDs.

  152. Hi
    My LED Bulbs are very dim
    (Simple water Level Indicator) ,please how it increase ,
    show me with simple diagram. Please as soon as possible.


  153. Seetharaman

    Hi Thomas your pcb may be leaky you may have to clean your pcb after soldering the components. the flux can produce a leakage path. if you are getting after connecting the probes then the probe wires are too long or not properly routed. in such adverse conditions you can use a 100k resistance with 0.1uF in parallel from each transistor base to common.

  154. Hi!
    I prepared the circuit diagram of simple water Level indicater , but its not working properly.
    Lights are very dim , please help me soon , how can i correct the lights.


  155. Thomas Mierzwa

    I soldered everything up and tested it on the bench. why do all the LEDs light up as soon as power is applied? They’re not at full brilliance. with NO level probe connected they’re dimly lit. but they do brighten slightly when continuity is established between the common and a level probe.

  156. Seetharaman

    Hi Thomas the lead resistance will not matter. try to use high efficiency LEDs. ensure the routing of the cable is through a metal conduit to avoid stay inductions. ensure the location where you measure the level there is no frothing or surge in level. if it cannot be avoided, use a bigger pvc pipe, with both ends open, to enclose all your probes, by which the level alone will be communicated to the probes.

  157. Thomas Mierzwa

    This circuit is going to be used to indicate forebay water elevation in a hydro-electric station. I made up a printed circuit board with ten transistors and associated resistors on it. The probe assembly is a piece of 1/2 inch pvc pipe with a common probe at the bottom and individual wires [probes] for each level at one tenth of an inch increments up to a foot. The total length of the probes and wire is fifty feet. Won’t the copper resistance of the wire have anything to do with the sensitivity? The power supply is a plug in 120 volt to 6 volt ac step down transformer with an output of 600Ma. My plan is to use a red LED at the lowest level, green LEDs for the intermediate levels and a yellow LED at the highest level. If you can spare the time answer me in regular email please.

  158. Seetharaman

    Hi Jack F is common, all others are level sensors. What is the type of your probes. are they insulated between them properly. Ensure that your PCB is thoroughly cleaned. If above checks are carried out it should work ok.

  159. Seetharaman

    Hi friend visited site and replied. I am enclosing my comment.
    Hi R1 to R5 has to less than 1K (470 ohms is practical)if the LEDs to glow to visible level with ambient light level.

  160. Dear Sir,

    I have built the circuit, but all leds D1-D4 glows even if one probes of A-D are put in water.

  161. Seetharaman

    Hi Jerome you can attach a relay by addind one more transistor you refer to my earlier comments. if you want to have the modified drawing pl send email to

  162. Hello sir, i also want to asked the same question…is it possible to attach a relay on this type of circuit?..i will also use this on my automated hydroponics system..thanks…

  163. Hello sir, is it possible to attach a relay on this type of circuit? I intend to add a relay to automatically shut off the water pump when the water tank is full. You reply will be greatly appreciated. Thank you…

  164. hello seetharaman i have send you mail( with an attachment having circuit diagram of amplifier please read the mail and reply me soon

  165. seetharaman

    Hi Atul please refer to earlier comment on Aug 29th, you have to use 1N4002 with 100uF to covert puslating DC available at the emitter to become pure DC before feeding into electronic sounder

  166. Works perfectly, modified bit to handle 8 leds (different color)


    an diode of which type and capacitor should be electrolytic one or other?????is it colpulsary to use this diode and capacitor????


    so should i replace 2.2k to 100 ohms but which i did the changes of supply would i be remain same?????

  169. seetharaman

    Hi Atul reduce 2.2k collector resistance to 100 ohms it should solve your problem. No other change is requires. Ofcourse rectifier diode and capacitor is a must. The above change will give your load around 25 to 30mA, which is sufficient for the LED and electronic sounder.


    Hello sir i made some different changes sir i changed the trasistor to CL100 it worked and i also changed the resistance value at base but when the probes were in water again the sound became low so then i changed the supply to 12 v to check then i faced a new problem that without giving the supply to base the transistor was on continiously………was it because of the supply………….so what i can i do further to increase the sound should i again change the trasistor to suit the supply if so then which trasistor can u tell me sir plzzzz……..?????????

  171. seetharaman

    Hi Atul it will affect the transistor. since it is ripple DC the volume is low connect from emitter through a diode to the electronic buzzer also connect a capacitor of say around 100uF in parellel with the buzzer this should solve your problem.


    Hello sir!
    I made project its working but my BUZZER sound output is weak its a continious 3-24V buzeer as our supply is 6v due to the resistor its affects more make the buzzer sound weak so can i put resistors of other value less than the given values and i want to ask that can i connect the probe direct to the base of transistor this makes the sound of buzzer strong but will it affect the transistor????plaese reply soon so as i will make the changes!!!!!

  173. seetharaman

    Hi Atul you can use 1-18 aluminum insulated wire (single strand 18SWG PVC insulated). expose just 10mm wire at the water end, two of this will be required. this will be your probe. connect one to 6 volt AC and the other one to transistor base through 22k resistance.

  174. Ya Atul u can it with ur water tank i use it n its working fine


    thank you sir for urs quik reply can i use this system in my water tank??? and those 2 probes can i use alumunium ones????an one probe connected to 6v and other 1 to the transistors base????

  176. seetharaman

    hi Atul you can use just 2 wires and one transistor with collector to LED and to an electronic sounder this will meet your requirement.


    I want to ask that when one probe gets elecrically connected the previous probe will be still connected on will get disconnect????plzzz reply sonn i am eagerly wiatin to do this project


    Hello sir,
    I WANT to ask that in this project there are to many LEDs connected this denotes that at each level at led glows but i want to ask that can we do one LED connection at last level and can we connect a buzzer to this ONE led connection means at final level of water along with this LED a buzzer will also start I WANT this connection at my home so plz tell me on small scale basis sie plzzz do reply can it be possible??????

  179. seetharaman

    Hi Ashu you ca use asimilar circuit with F and A probe only in the water flow pipe line . when water flows it will conduct when water flow stops it will go open and an alarm can indicate the dry run.

  180. Thomas Mierzwa

    where does the F probe connect in the circuit?

  181. Hi,
    This is a interesting circuit related with water tank. I have made one with 10 indicators and I also made up my Water Pump auto system so it turns “On” when water level of the tank goes down and turns “Off” when water level reaches to its top level.
    Now the problem is, in my area there sometime lack of water in the main water pipe line, I have attached ma Pump/Motor in the main pipe line for suction of water but sometimes Air catches in the Pump/Motor due to lack of water in the main pipe line, and the Pump/Motor keeps running without water and heat up and burns.
    So, I require a circuit which can be placed at the water flow end so that it can give a signal if there is water flowing or not.

    Please Help me,

  182. seetharaman

    Hi Manjit you can use DC it will work but the electrodes(sensor) will get oxidised soon due to electrolysis of water with DC.

  183. Can we use a D,C, Supply instead of Ac supply????

  184. seetharaman

    Hi Ram Mohan 1/18 is single strand (solid conductor) of dia 18SWG wire. normally used for 5Amp lighting house wiring.
    SS tubes of 4mm and 6mm id are available from instrument dealers.
    to avoid high reactions with water better to use low voltage which can be detected by electronic circuit hence i prefer around 3volt.
    i will mail you soon

  185. Ram Mohan S

    Hi Seetharaman,
    Thanks a lot for such a quick reply.
    The actual implementation was that I have dipped the output from the step-down transformer (6-0-6) which is an AC current into the water through the aluminium wires. The other wire receives the current from the probe dipped in the water. This is rectified using a bridge rectifier and given to the LED. This will be later replaced by the LED connectivity with connecting it to a 555 timer IC.
    But some how I saw corrosion happening to the wire dipped in the water after few weeks. Kindly let me know if I need to add any capacitors or any other circuit.
    As for the next step, can you kindly let me know from where I can get the stainless steel rods as these are not so commonly available in the market.
    What is the 1/18 insulated wire. Are they anything special wires or am I too dumb to understand :-(. Should we use voltage in the range of 3-6V or if a voltage of 9V is also OK.
    It will be great if you can provide me your contact number so that I can contact you for any more details to my mail id sram_mohan at yahoo dot com.

  186. seetharaman

    Hi Ram Mohan we use 1/18 insulated wire with 10mm exposed at the sensing point. even after one year of operation with low voltage AC (3 to 6volt AC ) the functioning was ok but very little colour change on both the wires.
    may be the water at your place may with more corrosive salts. you can try stainless steel rods in place of aluminum. this should solve your prolem. if this is also getting corroded, as a last resort you have to think of magnetic float and sealed magnetic reed switches, though expensive will be highly reliable.

  187. Ram Mohan S

    Hi Seetharaman,
    Some how my previous query posted here went unseen by the author. I can see some good number of posts from you in this website. I am desperately trying to make a probe for my water level controller but failing when working on it. I wanted to make an automatic controller using 555 timer, it needed a DC signal. So when the probe in the above circuit is an AC current I needed to convert it to DC. So to the return line I put a bridge circuit using 1N4001 and converted it to DC and gave it to a LED with resistance in series as load. I kept it in the water (Basically a Jug of water) for few weeks but still found that one of the aluminium probe inserted in the water was getting dissolved.
    Could you kindly help me in this matter?
    P.S: The water is a bore water so it will have some salt content.
    If this problem cannot be solved, do you have any other alternative ideas like some float device using which I can make use of a probe. Kindly suggest.


    Sir,i saw a circuit diagram details of the IC BA5406.But you do not mentioned their leg number.plz do the same.

  189. This circuit is very helpful especially in our home or in our piggery.

  190. seetharaman

    Hi you can use any insulated solid conductor of 1mm dia end around 10mm exposed.
    You can use float swiches but they are very expensive.

  191. can i use any wire for the probe? can i use a floating switch on an industrial project?

  192. shahensha

    dear sir,

    i need this circuit for my home purpose means water supplies to bathrooms and kitchen.the 6v current will make any harm to us.

  193. Edgardo Diolola

    Hi, Seetharaman Sir,
    Thanks a lot for the very kind reply.
    My best regards, and more power to you.

  194. seetharaman

    Hi Edgardo yes, base of 2N2218 to limit Ibe, even though R1 to R5 is available. Any medium power NPN switching transistor can be used. 2N1711, BCY59, 2N3904, Any transistor with a minimum specification of Vceo 40volt Ic 300mA Ptot 500mW. hfe 100 @ 100mA and Ft 100MHz, can take care.

  195. Edgardo Diolola

    Hi Seetharaman sir;
    Where will i connect the 1 kohm resistor, at the base of the transistor? What would be the other equivalent part number for transistor 2N2218?
    Thanks in advance.

  196. seetharaman

    Hi Edgardo You can connect a diode 1N400X (any one in the series) to LED anode (which ever the level you want to monitor) connect a filter capacitor say 47mfd (as the supply to this circuit is AC you will get 50Hz ripple at the LED) and connect through 1kilo ohms resistance to a switching transistor say 2N2218 and its collector through the 24volt relay to positive of a seperate 24volt DC supply, whose negative should be connected to LED cathode . Emitter of the transistor also to be connected to LED cathode. Pl donot forget the freewheeling diode across the relay.


    Sir, this is a very good circuit as I see it, also in the posts. Can we incorporate a relay output of 24 volts coil rating in behalf of the LED output? Any suggestive circuit, I;d love to buiuld one for this project.
    Many thanks and more power to your site.

  198. sumairaarshad

    sr i want also make sap (simple as possible computer)
    what can i do to complete this

  199. syed qamar

    i nned a ful description about an emergency light of lm317
    why we use lm317 ic
    why we donot use a potentiometer at place of this ic
    please help me to construt this in typical method

  200. I am a layman on electronics. However i made a basic water level indicator that signals when water level is full. I want to add relay switch to turn off the pump when water tank is full using the signal available. Can some one suggest how to connect the relay and the specification of the relay needed. Pump is 1/2 HP in capacity. 6V is available at the signal

  201. vivekanand

    circuit diagram for water level indicator using IC555

  202. Ram Mohan S

    Srikanth, What you say is true but that would be tentative of the tank getting full. This will turn on the tank for the specified amount of time irrespective of the tank getting overflowed or not getting filled to the desired level.

  203. if o/p was connected to the relay through timer. we can also control water level in the tank (by using simple 555 timer circuit which is in this site.)

  204. Ram Mohan S

    To turn ON or OFF, you need to connect the output to a relay. If you are well versed with the functionality of a relay then it can be easy to do so.

  205. using this design how can the motor be switched off automatically when the required water level has been indicated?

  206. Hey its really nice and cheap too..I’ve one suggestion..Can we fix small buzzer for tank full indication.

  207. Ram Mohan S

    I was having problem with the sensor and after reading your post, i also followed the same thing but with some modifications.
    We use the bore water and basically the water is a lil hard in my place. So i dipped one end of the AC output (9V AC- 500 ma) from the transformer in the water, and the other lead from the water to the full wave rectifier (4 diodes). i connected the other lead of the transformer to the other lead of the full wave rectifier. The DC output was connected to the LED. Initially it went on well. The LED started glowing well and the probes dipped in the water was also clean. But after a month, I have started seeing scales around one of the probe that is dipped in the water. Even though the LED is glowing I doubt how many more days will this connectivity go on. Could you kindly let me know if I am doing any thing wrong. As such I am passing an AC voltage through the water but rectifying it to DC when I get it to a load. But why am I seeing this scale on one of the probe.
    I want to enhance this circuit so that I can control it completely to turn ON and OFF the motor.

    P.S: I am using an aluminium wire dipped in the water.


  208. ajith vijayan


    in the circuit diagram ‘f’ is not marked..

    thank you

  209. twits4twats

    I am not having much knowledge about electronics.
    Your circuit seems to be really simple with minimum components.
    I am having small doubt about Resistance.You have mentioned as 1/4 watt. In small electronic shops they mention only the resistance value. Am I to insist on 1/4 watt while procuring? or just procure standard resistors.


    The power rating of a resistor is calculated. If the author has stated a 0.25 Watt resistor, then any rating above 0.25 will do. In fact, the bigger the better within reason.The 0.25 is typically allready overstated to prevent burn out. If the circuit asks for a 0.25 Watt resistor but a 0.5 Watt resistor is half the price, go for the 0.5 Watt. As long as it is higher rated than what was asked for then you are safe.

  210. s.saravanan

    dear sir,
    my name is s.saravanan,i was mail from tirupur i give small robotics circuits and details of photographic
    by best regarts,

  211. I am not having much knowledge about electronics.
    Your circuit seems to be really simple with minimum components.
    I am having small doubt about Resistance.You have mentioned as 1/4 watt. In small electronic shops they mention only the resistance value. Am I to insist on 1/4 watt while procuring? or just procure standard resistors.

  212. hi!:
    hi i probe ur circuit into an emulator, and it works, thats nice, but my question is that if we have to use 2 transformers or use the same t the bottom, and can u tell me why the leds turn on with AC if they are output comp of DC??

    • admin

      AC voltage means that it will have positive and negative half cycles. The diode will light only in the positive half cycles. Since the mains frequency is 50 Hz the diode will be blinking 50 times per second. Due to persistence of vision we feel that LED is glowing steadily.

  213. Dear Sir,
    Kindly send me a reply with more details about water electrode probe, please also send me a photograph too.

    Sincerely yours,

    • admin

      The probe i mentioned here is just insulated aluminum wires.
      Just remove the insulation on the tip of the wires for 1cm. Immerse it into the water as per the description in the circuit.
      Probe is ready.

  214. why do we need the transistor
    why cant we simply use resistors only
    i am talking about a very small scale demonstration project

    • admin

      the current conducting through the water is not at all sufficient the light the LEDs. The transistor acts as switch and will drive the LED connected to its collector.

  215. sir, i would like to ask you that if i will use single strain wire as probe immersing in water,will it create any problem? this wire we normally use for breadboard connection. sir plz do reply.

  216. Francy Kakkassery

    Dear Sir,

    Thank you very much for your message regarding the water electrode probe. I am satisfied with your explanation, and it is working properly.

    Thanks once again.


    • admin

      Happy to hear that you successfully constructed the circuit.Keep on.


  217. Francy Kakkassery

    Dear Sir,
    Kindly send me a reply with more details about water electrode probe, please also send me a photograph too.

    Sincerely yours,

    Kakkassery, Kerala, India

    • admin

      The probe i mentioned here is just insulated aluminum wires.
      Just remove the insulation on the tip of the wires for 1cm. Immerse it into the water as per the description in the circuit.
      Probe is ready.

      Still not satisfied ???? Comment here .I will give you a detailed description.

  218. alaa joujou

    From : Donia AL, Dawlyia Establishment.

    To : Export Manager

    First off all we do hope if you & your team ok
    We are a private Saudi Arabia company for all kind of water & oil level controller & we would like to be your agent for your water level controller in Saudi Arabia shortly.

    Finally, we are looking forward to hearing from you ASAP.

    Thanks …
    Marketing Department
    Donia AL, Dawlyia Est.
    Tel no: 00966-530279520
    Kingdom of Saudi Arabia
    Jeddah City.
    Alhambra Street.

    • Dear sir.

      can i ask a simple diagram or circuit using two sensor to indicate the low and high level of water in an open area? with a converter from 9 volts convert it to 220 volts. for example, determining the low and high level of water in a pond.
      Plsssssss help me…

      Thanks,,, im working with my project now,

      • If I would like to use the AC sensing and take the signal to interface with a uc, could you please make some suggestions. This will give us both AC sensing and uc side a DC signal from AC sensed signal.