Water tank overflow is a common problem which leads to the wastage of water. Though there are many solutions to it like ball valves which automatically stop the water flow once the tank gets full. But being an electronics enthusiastic wouldn’t you like an electronic solution for it? So here is a simple and handy DIY that will guide you to make a circuit which will detect the water level and will raise an alarm upon getting the water tank full or a preset level.

This simple transistor based water level indicator circuit is very useful to indicate the water levels in a tank. Whenever tank gets filled, we get alerts on particular levels. Here we have created 4 levels (low, medium, high and full), we can create alarms for more levels. We have added 3 LEDs to indicate initial three levels (A, B, C), and one Buzzer to indicate FULL level (D). When tanks gets filled completely we get beep sound from Buzzer.

Circuit Components

• 4 - BC547 transistors
• 6 - 220 ohm resistors
• 3 - Colour led
• 1 – Buzzer
• 5 - 9v battery + battery clip

Circuit Diagram

We can consider this whole circuit as 4 small circuits, each one for indicating/alarming, when a particular level (A,B,C,D) of water have been reached.

When water level reaches to point A, circuit with RED LED & transistor Q1 gets completed and RED LED glows. Similarly when water level reaches to point B, circuit with YELLOW LED and transistor Q2 gets completed and Yellow LED glows, same goes with point C. And finally when tank gets full (Point D), circuit with buzzer gets completed and buzzer starts beeping.

Working

Here we are using transistor (of NPN type) as a Switch. Initially there is no voltage applied to the base of the Transistor Q1 and the transistor is in OFF state and no current is flowing through collector and emitter and LED is OFF (See below diagram to understand Transistor Pin structure).

When the water level reaches to Point A in the tank, the positive side of the battery gets connected to the base of the Transistor Q1 through the water. So when a positive voltage has been applied to the base of the Transistor Q1, it gets into ON state and current starts flowing from collector to emitter. And RED LED glows.

You can see resistors (R1, R2, R3) at the base of each transistor, which is used to limit the maximum Base current. Generally a transistor gets its ON state fully when a voltage of 0.7 V is applied to the base. There are also resistors (R4, R5, R6) with each of the LEDs, to drop the voltage across LEDs, otherwise LED may blow up.

Same phenomenon happens when water level reaches to Point B. As soon as water level reaches to Point B, a positive voltage gets applied to the Transistor Q2, it gets ON and current started flowing through YELLOW LED, and LED glows. With same principle, GREEN LED glow when water level reaches to Point C.And finally Buzzer beeps when water level reaches to D.

Note that Left most wire in the tank must be lengthier than other four wires in the tanks, because this is the wire which is connected to positive voltage.

Video

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• Yashaswi
Nov 16, 2015

Will this work in a large water tank?

Oct 08, 2016

yes it will works on large tank also

• Joy Biswas
Apr 21, 2017

can i use this water lavel indecator for 500 liter tank ?

• Ankit
Oct 18, 2016

Yeahh it will definitely work for large tank yashh

• Kalaimani
Feb 02, 2017

Hi sir please send the Water level indicator using transistor

Oct 31, 2017

its a demo project...if u will make a large base project then it will work....bt d concept z same...

• Jayant
Nov 21, 2015

Of course, it will work, but you need a proper installation.

• kelly
Nov 26, 2015

can a (BC547 or BC548) transistor be used instead of the BC507 transistor

• Jayant
Nov 28, 2015

We are already using BC547 transistor, any General Purpose small signal NPN transistor should work here.

• Prakash Koppal
Nov 03, 2016

ya you can use ....or any other general purpose transistors also

• uk
Nov 29, 2015

Sir may I use it in my 1500L tank .. Will it woperfectly ? And me fast sir.

• Jayant
Dec 05, 2015

As previously stated, it will definitively work in any tank but you need a proper installation, concept will remain the same.

• pankaj
Dec 19, 2015

Sir, why not you have used resistor with the transister connected with the buzzer?

Jan 01, 2016

Yes, you can also use current limiting Resistor for the forth Transistor, to prevent it from any kind of damage.

• Priyanka
Dec 27, 2015

Sir, will it work with long wires like from terrace to room

• Raj
Sep 10, 2016

yes priyanka its working
before I complete the device and then I m using the device

• sourav shome
Mar 21, 2017

What wil happen if i do not use 220 ohm resitor?

• pragya
Jan 29, 2016

Sir pls help ..
I have arranged all rrquired components according to the given circuit bt the circuit gets completed at the transistor level nd the led strts glowing as i connect the battery to the circuit without placing those other ends in water .. Help me sir ..

• mish
Oct 09, 2016

hi same thing happening with me too. I made 2 circuits and 1 led glowed when i connected with the battery and with the 2nd circuit the buzzer is buzzing without pouring water. The circuit looks right but idk what the problem is? Can you help please. Thanks

Jan 29, 2016

Sir
I am making your project but sir me use transistor bc548 so sir any problem

• muzzammil
Feb 06, 2016

i want to attach buzzer on each LED then what should i do, please guid...
thx

Feb 08, 2016

you can directly connect Buzzers with LEDs.

• Cesar
Feb 10, 2016

Sir

How long is the maximum distance in meters form a 5 volts or 9 volts battery ? Like with an UTP network cable.

• vineet
Feb 12, 2016

Dear Sir,

My query is that I want to install the system at ground floor and put the wires in the water tank located on second floor. For that I have to pull the wires for approximately 40 feet . So for such a long length wouldn't there be copper losses and would it function with 9V battery

• Jayant
Mar 11, 2016

The voltage drop is dependent upon the resistance of wire, load resistance and current through the wire. But roughly according to this circuit, we can use it upto 100-150 feets. You can check some online voltage drop calculators to find the accurate length according to your wire.

• vikram shetty
Feb 27, 2016

Sir as on 28 Feb we are celebrating science day I am going to exhibit this model but sir.... Asci have tested once I observed that the Buzzer will not scream loudly as it just sounds in small amount only like a whistle. so myvdoubt is ... Is this buzzer will be able to warn the person.... Plz reply

• Jayant
Mar 11, 2016

You can either use some Alarm with external power supply and transistor as a trigger or You can use AC alarm with a Relay in place of Buzzer. Check How to use Relay here.

• Siyam
Mar 22, 2016

Hi, I have made this water level indicator but it is not working properly because the water is not connecting the wires inside it. However when I put salt in the water it works. If possible help me in this issue.

• Jayant
Mar 29, 2016

Probably you are using Purified Water or Distilled Water, which does not conduct electricity. And after adding salt (ionized substances), it becomes conductor.

• Naseer Hakeem
Mar 26, 2016

what is the limitation of this project?

• ankit tomer
Mar 29, 2016

sir, i have completed this project on pcb board with proper designing of pcb.but the problem is that not even a single LED is glowing.can you please suggest where may be the fault??
and sir i have connected the base of the transistor to the sensor,emitter to -ve termonal of battery and collector to LED.Is it right,sir??

• Jayant
Mar 29, 2016

This is a very simple circuit and should work without any issue, have you connected LED terminals properly according to polarity.

Mar 29, 2016

Can I connect a motor instead of led or buzzer??
Once water reaches certain level , motor should start??

• Hasan
Apr 01, 2016

Sir,
Can I use motor by replacing the buzzer ??
Is any possibilities here when the water will have reached the top of the tank then the motor will off??
I mean the pump motor which is using to enlarge the water level of the tank!!
Can I use motor by replacing the buzzer ??

• Abhishek
Apr 02, 2016

@Hasan and @Sunny Yes you can use Pump motor. A Relay will be used for this. To switch Off the motor, use Relay with PNP transistor and to switch On the motor use Relay with NPN transistor. Check this for Relay connections

• amit
Apr 02, 2016

Shall I use 12 v battery instead of 9 v

• Vikas
Apr 02, 2016

Why do we need the transistor, i know that it works as a switch here, but what happens if i directly connect the led cathode to the wire and drop it into the water instead of connecting the transistor? Theoretically it will work, but what happens if I implement it practically?

• Abhishek
Apr 17, 2016

Water is not a perfect conductor, but it can conduct enough to trigger Transistors to Glow LEDs. Hence Transistor is also used here as Amplifiers.

• Shubham Sawant
May 27, 2017

You can do this by increasing current of supply by using mobile charger or else and check with multimeter to find excess voltage to use appropriate resistor.
I have made such a working circuit and using it in perfect working condition.

• Sunaabh Sarkar
Oct 30, 2017

Most mobile chargers are small SMPS devices that reduce the mains voltage to 5.1v etc etc, and usually there is no isolation of the mains from the output, so one runs the risk of electrocution if a mobile charger is used to run the device so a mobile charger would not be a good idea to power the device. Use a 9v battery or a power supply using s step down transformer... the battery eliminator kind of thing.

• venkatesh
Jun 29, 2018

conductivity of water is less compared to conductor.power loss is acquired in water so it not enough for gloving led.we are using trasister required 0.7v input for switching transister.

• anusha
Apr 03, 2016

Sir ,What happens if we change the resistor values?? And can i replace the buzzer with an 8 ohm speaker.if yes shall i need to connect resistor at fouth trasistor also??

• Joe Jose
Apr 07, 2016

Hi, I have made this water level indicator but it is not working properly because the water is not conducting elecyricity. If possible help me in this issue.

• neel gohel
Apr 08, 2016

Can i used bc-548 transistor?
Nd can i used 470 ohm registor insteand of 230ohm registor?

• Abhishek
Apr 17, 2016

@Joe: Check above comments for Water conductivity problem.
@neel: Yes you can use BC548 and 470 Ohm resistor

• mahi
Apr 11, 2016

may i use transformer instead of 9v battery?

• Gopi
Apr 13, 2016

• Shanmuk
Apr 15, 2016

May I get single led glow at particular level.if possible can you suggest me sir.as I am facing difficulty with that.

• som
Apr 15, 2016

Dear,

The buzzer will produce a steady sound. Instead of that, if I need to sound like a siren, then how I can achieve this. I assume some capacitor/resistor may solve the problem. But I don't know how to connect those components to the base of the transistor.

• som
Apr 15, 2016

Dear - How to make the buzzer sound like a siren instead of just producing a steady sound?

• falesh
Apr 16, 2016

Can I increase the no of LED indicators to 7 by repeating the Transistor circuit 4 more times?

• Yogendra Singh
Apr 19, 2016

hello

i made the circuit according to above shown figure but i connect mobile charger as a source in place of 9v battery all LEDs works fine but there is problem with buzzer there is no sound from it when i complete circuit by dropping wires in water tank but it works fine if i connect wire directly..

• Gayan
Apr 21, 2016

Sir
How can use this circuit reverse type. Because i wan't measure water level in my water well. Actually I want low level indicator. Water level is gone down i want indicate the led. How can use this. Pls help me.

• Abhishek
May 06, 2016

Use PNP transistor BC557 in place of BC547 and reverse the order of LED/buzzer.

• Lokesh
Apr 26, 2016

What is the least Price for this indicator??

• Aju mallik
Apr 29, 2016

Thanks sir.

• Tahir Aleem
May 04, 2016

sir which type of transistor we are using in this project i mean pnp or npn???

May 12, 2016

sir can we make this circuitju without transustor and resistor...

• mehedi hasan pavel
May 15, 2016

sir,how much money to be used for this project?

May 17, 2016

This demo project can be made in less than 100 Rupees.

• Junaid
May 17, 2016

The circuit is complete when voltage flows through the water.. But if the voltage flows, then the current may also flow. So, if I use it for my houses tank, would current flowing in the water be a problem, or the water does not get electrocuted, please do give me a quick and sufficient answer.
Thanks.

Jul 12, 2016

Yes current will flow through the water, but current from 9v battery is not harmful.

• ajithkumar g
May 24, 2016

Hear after I try this

• Dureste
Jun 10, 2016

Thank you for the briefing man! but is it necessary to use a battery? is there any change that would happen if i apply a bridge rectifier circuit instead of battery? if yes, do i have to change the resistor value if the output of rectifier is 12v?? thanks man.

• dharmendra
Jun 13, 2016

Sir.. I complete the ckt. Of water level indicator bt one doubt is that if my tank is full then buzzer will start bt till the level of water is full the buzer will operate on for long time so how i can stop to this

• kaushik
Jun 14, 2016

Dear sir,
How we convert 5-9 V into 220/230V ??

• Bobby
Jul 02, 2016

respected sir
can i use transformer in place of 9 V battery and motor as buzzer
if yes
what will be connection

• Waqas
Jul 10, 2016

For how long will the buzzer sound? I mean, once you are alerted, how can you stop the sound of buzzer? turning the circuit off wouldn't be a good idea as it would be in efficient to turn the circuit on and off again.

• vipool
Jul 11, 2016

the buzzer used in this ckt is having very low sound . i want to increase the strength of the buzzer or use some other device for that purpose. what is the solution for dat?

Jul 12, 2016

Trigger some 220/110V AC alarm with the help of Relay and be careful while working with 220v, it can be lethal.

• Muhammed Hussei...
Jul 15, 2016

i need help on this very topic of the project.

• sandeep
Jul 21, 2016

will i give home voltage to it

• waleed
Jul 26, 2016

why not we use PNP instead of NPN. let suppose we use PNP what will be the impact on the circuit.

• Arun
Jul 29, 2016

Super idea sir...But I have to implement using wireless technique sir..I have an Arduino board..Give me an idea sir

• Abhijeet Gawande
Aug 01, 2016

Sir, the circuit is working properly on 9v battery.but I have used a 9v transformer here and seven colors led .the problem is that,I am getting the output but the led's a are not blinking and the buzzer is not making proper sound.

• John
Aug 04, 2016

If we add a diode in the forward biased direction anywhere in the circuit, will it change the outcome?

• shiv singh
Aug 24, 2016

Transistor burn when prob short please give the solution of prob short transistor not burn.
Thanks
shiv singh