Two tank water level indicator using ULN2003

Hello Guys,
Please help me out with this model as 'm struck.

I've a built a ckt which uses simple conducting wires to indicate water levels (12V DC wire at bottom with 3 levels --low , middle and top). This is same for underground tank and over head tank. I'm using LEDs total 6( 3 for overhead tank and 3 for underground tank) with 100 Ohm resistor connected to ULN 2003. These LEDs are driven by 5V supply.
Anode connected to common 5V and cathode to the pins of ULN2003 output via 100Ohm resistors.

The problem is the 3 LEDs are getting faded for overhead tank and get OFF even though the water is present in all levels.

Also the power supply i'm using Adopter(12V 500mA) Bridge rectifier followed with filter and IC7805. IC7805 is also getting hot if its ON for more than half hour. I want to keep this ckt ON for all the time. Please let me know how to rectify this problem. I later intend to make a water level controller, But i'm struck with this itself.:-|

Please post the schematic.

The ULN2003 is not the best device to use in this applicaton because it needs a relatively high input current to saturate the output transistor, you might be better using a CMOS buffer or inverter which needs less water conductivity to operate and also gives a more sudden output change as the input voltage rises and falls.

I would also suspect your have a problem with the flow of current through the two tanks. For example, are they metal tanks and if so, are they electricaly bonded together?

The only way you can reduce the temperature of the regulator is to fit a heat sink to it. The power it dissipates is (Vin - Vout)/Iout or about 7 Watts per amp. There is a possible way around your problem, if you use a CMOS buffer to sense the water level and use it to drive a ULN2003 you might be able to remove the regulator altogether and run the LEDs from the 12V line instead of the 5V line. 4000 series CMOS will work up to 15V supply so you might not need the regulator, 74C series will neeed the regulator but moving the LED power to the 12V rail means the LED curent doesn't flow through the regulator and it should run cooler.

Brian.

Is the attached diagram looks like what you have connected?

I am using 3x500Ω resistors and 3 push buttons to simulate the water resistance and water levels. R16-R18 are pull-down resistors used as voltage dividers. It should be adjusted until the LED just works. try different values if 10K doesnt work.

From your description I assume your 2 water tanks are separated and not one tank 50% on the surface and 50% underground.

If your wiring is different, please amend mine so I can simulate again.

Allen