Introduction: WATER SENSOR'

Make a simple circuit of a water sensor by using a few electrical devices. Don't trust just try it yourself.
They are-
1) NPN transistor.
2) Switch.
3) Two 500 ohms resistor.
4) A 10kohms resistors.
5) 0.01 capacitor.
6) 0.001 capacitor.
7) A LED ( 1.5 volt).
8) A 3 volt power source.
9) Basic tools



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    20 Discussions

    Where is the video showing us to make one

    can i ask what is the number of the NPN Transistor cause i can't buy it in the store without the number.

    cant we make the led off totally when the probes arenot immersed into water?

    cant we make the led off totally when the probes arenot immersed into water?

    cant we make the led off totally when the probes are immersed into water?

    also you might want a 470 ohm or a 510 ohm resistor (or two 1k in parallel)

    You're doing something really weird there. The NPN transistor is reverse biased, as drawn And the capacitors are completely redundant.

    You've got a total of 1Kohm limiting current through the LED, this is a bit much for a 3V supply surely?
    NPN transistors should be connected +ve to the collector and -ve to the emitter (you've got it the other way around there) and you don't need a big heat-sunk one for 1 LED.
    Are the low-value capacitors necessary?


    6 replies

    i have got a total of 1kohm resistance limiting the current of led so that it can't light up when the probes are not in water.when you will make it you will see that the led will light up (when the switch is on) a little because of resistors but when you will dip the probes into the water transistor amplification will take place and the led will be brightened.
    no capacitors are just placed there to avoid the loss of electric current. if you will use some higher value capacitors you will need to increase the voltage provided.

    When the probes are not in the water the LED should not light at all, with/without resistors - at 1K it will be dim?
    I stil don't understand the function of the capacitors, even with reference to loss of electric current.


    it will be according to the power applied that the led will light up or not
    here the transistor is acting like a potentiometer which is leading the led to get brightened when we apply a little amount of current in base ( by dipping the probes into water)a large amount of current will flow from collector to emitter this is the basic property of transistors. ( amplification effect )
    here capacitors are conserving the currents. they act as a battery which stores the extra charges that are not needed in the circuit.

    capacitors are conserving the currents. they act as a battery which stores the extra charges that are not needed in the circuit.
    But the thing is powered by batteries, there is no need to store charge elsewhere. And those values are too low to store much anyway (I don't understand...)
    I do know how transistors work though.


    suppose we have a 1.5 volt led and a 2 volt power supply we have lighted up the led so the voltage that will be unused wil be stored by the capacitors.
    the charged capacitors will provide currennt when the power supply will be off.
    (capacitors are just two plates of conductors separated by a semi-conductor.they allow the ac currents to flow but they block the dc currents.)
    transistors are made through semi-conductors. they work due to the special behavior of semi-conductor due  to electric currents. a small amount of current in base will force a large amount of current to flow from collector to emitter.

    I do know how transistors work, I do know how capacitors work.

    You seem to be missing some basic electronic knowledge:
    Voltage cannot be stored
    The extra 0.5V in the 2V/1.5V system is across your resistor(s).
    Again, those capacitors are too small to store much charge, they're the "AC currents to flow" type.


    It lights without water because ther is no path for the base leakage current. Need some high resistance value from base to emiter to keep the transistor turned off when no water is present. this could be 100K or more depending on the Transistor.   I think it woulr also be better to haave the emmitter in the Collector leg.  giving the cathode a ground(-) shot. The emitter has a low output inpedence.

    1 reply

    Functions it on distilled water as well as tap water? I say this because distilled water is almost totally non-conductor.

    1 reply

    Hmmm, I like your circuit diagram, but what will the finished project actually do?

    1 reply

    this project will just measure the presence of water. when we will switch on the switch the led will glow a little but when we will dip the probes into water the led will get brightened depicting the presence of water.