Water Level Indicator System project

hi guys, my self ankit shyani. i am second year student and studying at west kent college located in Tonbridge, kent. i am doing project this year and i am making water level indicator system. i have some query about my circuit. actaully my circuit based on very simple IC chip CD4066. I tested the circuit on breadboard first. When the water is empty the wires in the tank are open circuited and the 180K resistors pulls the switch low hence opening the switch and LEDs are OFF. As the water starts filling up, first the wire in the tank connected to S1 and the supply are shorted by water. This closes the switch S1 and turns the LED1 ON. As the water continues to fill the tank, the LEDs 1, 2 show up gradually. but when the water get to level 3 , the led3 and 4 will turn on at same time, i dont know why LED 4 also turn on when its get to level 3 . i am attaching the circuit diagram if someone can give me some suggestion it will be greatful. Thank you

Hello,

I think there is a short between the sensors from 3 and 4.
I doubt if 4 will work. The transistor takes much more current as the cmos input.
The current must flow through the water to turn on the transistor.
This can only work if the water is "contaminated" with someting like salt.

Greetings,
Bertus

Bertus is probably right. What you might do as a trouble shooting proceedure is
0 Put a capacitor or an RC filter on your board to decouple the supply voltage. (This, in case the signal from 3 is triggering 4) Otherwise...
1 substitute another 4066. If it doesn't work then...
2 change the location of your chip and resistors on your breadboard (this has helped me in the past whenever mysterious things happened. Lastly, ...
3 Put a buffer between the transistor and its input signal.

As already stated, you probably have a short somewhere that's causing the fourth chip to turn on when three does.

I have no problem believing that that you will get enough base current through the water to turn the transistor on. Radio Shack sells piezos that draw as little as 5mA. If the transistor has a gain of 100 and the Piezo needed 10mA, then a mere 100uA of base current will turn the transistor and the Piezo on. I think I would use an emitter follower though.

If the buzzer is a low current Piezo, have you considered connecting it directly to pin 10, thus eliminating the transistor altogether?

Note: Water doesn't have to be contaminated to conduct. Only distilled water has little or no appreciable minerals in it. Tastes bla too!

hey
Why dont you have reed switches along the glass or container and have a float and a magnet, so when the magnet reaches the right level it will activate the reed, or a more crappy idea you could place Aluminium tape at seperate levels inside the glass with there own wire, and still with the float, but maybe have some aluminium contacts on it, Also check your circuit board because what was stated before may be true i also think there is a short in the 4 and 3 wires. Good Luck !

hey guys......thanks to all of you for your advise.. i am really appreciate..and it all work with sudden.. actaully the problem was there was leakage between S3 and S4 wire thats why... the problem was occuring.. now its works correctly....thank you all guys again.

From,
Ankit