Step 2: The Circuit

It has numerous transistors acting as a switch and the switch gets activated when the sensors tell them to. 

The heart of the circuit is the transistors BC 547. There are total7 transistors in the circuit and each one will be sensing the level of water present in the overhead water tank. There is one extra power LED without a transistor and that is because this Red LED will be telling us two things. Firstly when you power the unit it will be monitoring the power present in the unit and secondly it is also the indicator telling you that there is no water at all present in the tank. As because the water level is below the No. 1 (as shown in the circuit) sensor, no LED's will be lighting up, but only for the one Red LED. Therefore when you switch on your unit if you see only one Red LED lighting up then you know that the is no water present in the tank and therefore you should make you water pump on.
Then as shown in the figure i have given all the LED's in various color. Starting from the beginning is 
  1. Red LED (Indicating no water in the tank as none of the sensors are getting contact with the water)
  2. Red LED ( Level 1, indication very low water in the tank )
  3. Yellow LED (Level 2, indication of low water)
  4. Yellow LED (Level 3, indication of 1/4 of water in the tank)
  5. Green LED (Level 4, indication of half of water in the tank)
  6. Green LED (Level 5, indication of more than half of water)
  7. Green LED (Level 6, indication of nearing filling up the tank)
  8. Blue LED(Level 7, Full indication of tank and buzzer comes on)
Now as the water starts to rise up the sensors starts to get in contact with the water and the transistors are activated and there is a flow of current in the transistors making the LED's light up. Here in between the transistor and the LED there is a current limiting resistor 470 ohms, the job of the resistor is to checks that the LED does not get over voltage and destroy the LED. The transistor is biased by a 470K resistor with the ground and the sensing part is taken from the collector with a 33 ohms resistor going directly to the tank. As i have shown in the diagram the signals are drawn in the Green color. There by you can follow the LED's as they light up from Red to Yellow and then Green and finally to Blue making a sound.  

The Buzzer Part
Here you can add any of the normal buzzers that are readily available in the market and if  it is not then you can make yourself with a simple 555 IC. I am giving a small circuit diagram, it is really simple to make and there are minimum parts. It is a simple audio oscillator. I have also provide a circuit diagram here but if you are able to manage a buzzer then no need to assemble this circuit.

The Power Supply
This section contains a transformer converting the mains voltage 220V bring down to 9V. There is a bridge rectifier containing 4 diodes and making the Alternating current to Direct Current. After the filtering the voltage is then directly fed to the voltage regulator (7805) with a filtering capacitor. From the regulator IC the output voltage is then again filtered with a capacitor and is fed to the circuit. This comprises the power supply of the device.

This completes the electronic part of the project and now i will be going to the sensor part, which is also made easily.
<p>HI</p><p>I like yours idea. I made on similar steps but with different concept. It WIRELESS.</p><p>You can check this on my website <a href="http://www.vapory.in" rel="nofollow"> www.vapory.in</a></p><p>or buy online </p><p>http://www.snapdeal.com/product/vapory-white-wireless-water-level/636257896076</p>
Hi I m need this product
Not to hijack the OP's thread, but a big difference two years makes. Now using wifi Particle Photon board, Blynk, and IFTTT to remotely monitor w a smartphone app and receive notifications when my water level is low. Also sends a trigger to text my water supplier that I need a fill automatically. All inspired by this original instructable.
<p>Nice to see how you've it translated to an IoT app</p><p>Is there some instructable available ready for</p>
Afte 15 days of installation, the intensity of lights decreased.<br>The lights are dimmer than before.<br>Plz fin solution
<p>Can't just simply use a 9V adapter rather than using a transformer for the same operation ?</p>
<p>Yes, I think. (Only use DC!)</p>
Sir I made the circuit as above ..But the led glows without connecting to water tank...Please help sort this problem asap
Is it work with 20meter long wire
<p>I wish i found this earlier. I made something like this, but perhaps designed poor, because i was worried voltage loss in of 25 meter wire (LAN Cable), So after the failed experiment with transistors, I have switched to arduino and to justify my path I also added rgb leds :P with abilty to change color of filled / empty indicators, not to mention buzzers on low level and little buzz for over flow. <a href="http://inoace.com/blog/water-tank-level/" rel="nofollow">http://inoace.com/blog/water-tank-level/</a></p>
A few people had asked what switches I used, including a recent email. Just search ebay for tank float switch. They're plastic and sealed and are designed to be submerged.
<p>what will happen when we use npn transistor instead of pnp for water level indicator</p>
<p>While using npn, the led will glow if the contact did't connect.If you need so you can add another npn with the pnp.</p>
<p>If we use 'carbon brush' as sensors we can remove the metal rusting.</p>
<p>i'm looking for a water level sensor that i can mount on the floor and yet it can still detect level of water without exposed wire needed.. some kind of laser/wave detector.</p><p>is it possible?</p>
<p>You can use some floating-type sensor!</p>
<p>Hi!</p><p>Please let me know if a 9 V DC battery can be used instead of the setup you used?</p>
<p>Is drinking from the water that is being measured a problem?<br>I was wondering if the wiring could degrade into the water and cause an ingestion hazard.</p>
<p>hi raikut,</p><p>I connected 6v relay across led + resistor (470 ohm), and relay is operating when led glows. will it be okay or will harm the circuit after in future?</p>
<p>The circuit shows an NPN transistor and the positive of the supply is connected to the emitter through the LED and the collector goes to 0V. As this is a NPN transistor the collector should be positive in relation to the emitter. Can you please explain how the current flows through the transistor.</p><p>Thanks</p><p>Kamal</p>
<p>Hello friend, great job, perfect design, since the build and tested, but a doubt arose friend, in the scheme you mention two capacitors for filtering the source, but did not specify the value of them, by chance would be a 1500ufx16 volts? or is greater or less?<br>I 9volts using a battery for testing, but the battery does not last all, and the source is an alternative exelente.<br>Again, thank you for submitting your project and to share with us your esperi&ecirc;ncia, which by the way is very good and will help me a lot.</p>
<p>can i use 9v 500 mA Transformer for this project. i circuit is working fine when i touch to wires of +5V and level 1 detector. but when i submerge in the water. It is not working</p>
nicoo...made it ...its simple nd efficient..<br>
<p>great project</p><p>can i place your project on my website.</p><p>i'm working on a website which is related to electrical projects.</p><p>i also mention your name, link and other info.</p><p>plz reply</p>
<p>i want depth in deigning</p>
<p>what if we don't use Power Regulater 7805????</p>
Ic work on 5v. So by 7805 we supply circuit or otherwise it get short
<p>Beauty of this design is in its simplicity.. i personally feel only problem is to many wires between water tank and indication panel (if 10 feet distance , then total mess)<br>. this wire count can be brought down to only two wires if DAC is used on water tank side and ADC for indicator site ,furthermore voltage level for DAC to ADC are of significant value (13v app) so distance between tank and indication panel. </p>
<p>are all the grounds connected?</p>
<p>is it okay if i only use 4 levels or transistors (0% 25% 50% 75% 100%)</p>
<p>the power supply is 9v or 5v ?</p>
<p>You can use either 5V or 9V...:)</p>
What if i use a12v adapter
<p>can any one please tall me the exact materials i am going to use and how many of them because im gonna try to do this project </p><p>thanks :)</p>
<p>thanks raikut for this project.. ive made every exactly you have written but the sensors in overhead tank gets corroded in just two weeks . after that the buzzer sound gets low and some LED's start flickering. pls telll m some solution on this.</p>
Hm I also have same issue , what I do is cleanup wires every month :(
<p>Hi,</p><p>Have you tried anti-corrosive(AC) materials like AC paint or AC powder which are available in market. I am also planning to make one for my home.</p>
<p>This can cured by using a float that is sealed and designed to be in water. It acts as a switch. I have two 2500 gallon water tanks with 5 floats attached to it. No problems and works flawlessly. Electronics submerged in water will only last for so long due to electrolysis, the same phenomenon on outboard motors which is why they have zinc plate that is softer than the metal for the motor. So it eats away slowly at that instead. Email if you want help.</p>
<p>Hello Jason,<br>Can you provide the details on how to construct the floats?<br><br>Will be much obliged :)</p>
<p>can you pls send pic of tht switch?? or its web link.</p>
<p>Hi! Can I ask what is the value of the capacitor and the wattage? Do we use 2 or just 1 capacitor?</p>
9v adapter
can use 5v adapter
<p>can i use 560k ohm resistor in place of 470k ohm resistor for biasing the transistor and also i am applying 12v dc current to the circuit?????</p>
<p>can i use 560k ohm resistor in place of 470k because it is not available in my place and also i am applying 12v dc to this circuit..</p>
<p>i am so much impressed by this project i just love it and im going to make it for my class project.</p>
<p>i have made it but my family is afraid of installing it they are afraid if it will very dangerous to work with taps when this circuit is in on condition</p>
Don't worry... This circuit uses 5V DC which will not give you an electric shock. It is perfectly safe.
What is the longevity of the probe ? Sooner or later it is going to rust and it will be virtually cut off from the water... So which material should we use ?
<p>Hi friends,</p><p>One of my friend has build this Water level indicator to keep at his home. But the water seems to be non-conductive. Its acts as an insulator. Even We did check with multi-meter on the continuity mode. but still no conduction is happening. I am not able to resolve his problem. Could anyone help me on this... </p>

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