Simple Water Level Indicator (Help)

[SunnyRulz]

hey...!!
in the given circuit...i cant figure out the function of transistor...!!
ie. is it acting as a switch or an amplifier...??
Its a BJt pnp transistor...!!
If it is acting as a switch...then mode of its operation must be "saturation" or "cutoff"...but it is operating in active mode...??
please help...!!

**broken link removed**

 

[Ove]

The transistor works as a switch, but the Leds are turned the wrong way and will never ligth, and frankly I think the conductivity of fresh water (it is water rigth?) is far to low for the transistor ever to turn on, but I don't know. By the way shouldn't there be some kind of pull up that keeps the base of the PNP high when water level hasn't reached it?

 

[SunnyRulz]

The transistor works as a switch, but the Leds are turned the wrong way and will never ligth, and frankly I think the conductivity of fresh water (it is water rigth?) is far to low for the transistor ever to turn on, but I don't know. By the way shouldn't there be some kind of pull up that keeps the base of the PNP high when water level hasn't reached it?

yeah...i have turned to leds to the proper configuration...and the circuit is working fine...just want to know about the working of transistor...!!

 

[ericgibbs]

yeah...i have turned to leds to the proper configuration...and the circuit is working fine...just want to know about the working of transistor...!!

hi,
The design is ideally the transistors are either On of Off, so they are being used as a switch.

I expect that the water, depending upon its resistivity could also make the transistors work in a linear mode, if it limits the base current to a low value.
It really dosnt matter providing the LED's are either On or Off..

Dont forget, the electrodes could corrode.