Step 2: The Circuit

Picture of The Circuit
555 tone generator.jpg
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 total 7 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.
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Nice one. However, one problem with such circuits is the corrosion of electrodes due to the high current. I've been using this water level indicator circuit for several years and hardly needs cleaning. Maybe its the low current needed to trigger the CMOS IC switch.

Tutancof1 month ago

If am not wrong your buzzer circuit need additional connection for 555IC pin 4 and 8.

Tutancof2 months ago

Can i use any kind of 555 ic NE, NA, SA, SE????

srikarb6 months ago

Can i use just 4 levels instead of 7 ? if yes then do i need to change the transformer ?

u can use no need to change transformer

ananrafs110 months ago

can i use a 9v Battery for power supply ?

ananrafs110 months ago

can i use a 9v Battery for power supply ?

mownika1 year ago
wat r the specifications of transformer n diodes
raikut (author)  mownika1 year ago
You can use an IN4007 diodes along with a transformer of 9V AC with an input of 230V
saish0091 year ago
please reply its urgent, tell me WHERE TO CONNECT all the GROUND CONNECTIONS
raikut (author)  saish0091 year ago
The Ground connections should be connected to the negative line of the regulated power supply
saish0091 year ago
raikut, can i use 9V volts 500 ma transformer
saish0091 year ago
hey raikut please help with the circuit diagram whats the value of the capacitor after and before 7805 in the circuit diagram
raikut (author)  saish0091 year ago
the filtering capacitors you can use a 220uF/16V for the input connection and 47uF/16V for output, it was already discussed earlier in the comment section. If you have more questions to ask please see the comments below and if you don't find any answer then you can ask me the question.
saish0091 year ago
yajuj1 year ago
plz reply soon..... instead of grounding them i have connected the points(those at the collector end of the transistor) to the negative of the battery. will it create problem ......plz reply i have only one day left ......
yajuj1 year ago
hey raikut plz reply..... do i need to connect the transistor forward biased or reverse biased
and my power supply is 4.5 v it ok...
seethasub1 year ago
There is mistake in showing collector and emitter of the transistors. Collector should go to positive hence LEDs cathode should be connected to collector of BC547 and emitter should go to common negative line.
raikut (author)  seethasub1 year ago
This issue has been discussed earlier, please go through the comment section and watch the given video

aalexandru22 years ago
Hi, it is a usefull circuit and a thank you for it! I was wondering if you can help me with a additional circuit tu amplifiy the outputs(led's) so I can turn a 6v relay.
Hey Raikut.. , I tried a lot but could not get the transformer's connection . Can you explain me, how can I find that which among the three wires of the output is of ground??
raikut (author)  Nimmi Thakur2 years ago
The middle is the ground. But what is the voltage specification of the transformer.
Is it 5-0-5???
charmquark2 years ago
I have few doubts regarding the working.

1) What is the purpose of using transistor in this circuit?
2) I noticed that the LED is connected to the emitter of the transistor, and from the conventional current direction, current must flow away from the NPN transistor, but in this case, the current would flow into the transistor. Wouldn't that make it reverse biased? I maybe missing something. Can someone please explain its working mechanism?
raikut (author)  charmquark2 years ago
Please check the diagram above and you can see the transistor testing video and the picture here that i have posted

And one more question that can i use a 5v adapter with that voltage regulator along with capacitors...if yes then which capacitors should be used. and if no please tell me the transformer number and about capacitors and by the way what is the output of the transformer....

And i am directly solding it to board..but now i will try this firstly on bread board then on PCB.... and is their any prob in my transistor....
raikut (author)  aditya swaroop2 years ago
Okey let me explain, Firstly the 5v regulator you are using, and those regulators have capacitors you've said. Well capacitors only will not regulate the voltage. You will need a stable power supply. Use LM7805. I have shown in the circuit diagram.

For the Transformers you can use a 250mA transformer with 220v going in and 9V (output) secondary tap.

Secondly you can use a diode IN4001 to bridge rectify the voltage and give it to the regulator IC (LM7805).

And lastly for the filtering capacitors you can use a 220uF/16V for the input connection and 47uF/16V for output 
nice instructable,i have a doubt in my mind that which relay should be used in the circuit for adding a small water pump ....plese explain me ...
raikut (author)  aditya swaroop2 years ago
You can use a 9V compact relay to the bottom 2 LED. But you will only be taking the signal. You should be using a transistor for controlling the relay as i  have given a sample circuit diagram in my comment section. Also note that the Ground connection should be connected to common.
Will the buzzer(alarm) will continuously beep when the tank is full and blue led has lighted up...i yes how to control that buzzer to just beep once and then shutdown....
raikut (author)  aditya swaroop2 years ago
The simple answer is to put the power off to the unit as you don't need to keep the unit on all the time. Just turn it on when you want to see the water level and then turn it off.
But still if you want to automate the you can use an Arduino with a program, it would be complex but you can add it.
TheStudio72 years ago
This is an awesome instructable, very well put together and a great idea for water tanks of all kinds!