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i made an water level indicator using IC: ULN2803

Refer: Easiest water level indicator

Block diagram

It works well when used on glass of water, but when connect to my rooftop tank all the leds slowly diminishes and turns off. I think this has to do with high resistance of the tank water, but i doubt it since it worked well for first few days.

i am not any expert (clearly) so any help is appreciated.

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  • \$\begingroup\$ Certainly @user156047 is right. You might use a pushbutton to power the circuit only when you want to read the level. \$\endgroup\$
    – Dorian
    Dec 27, 2018 at 10:10
  • \$\begingroup\$ @Dorian ok, let me try with non corrosive metal strips and get back. \$\endgroup\$
    – Alex Robbin
    Dec 27, 2018 at 10:17

2 Answers 2

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I'm not big in chemistry, but I believe that it has stopped working because of electrolysis. In other words your contacts have corroded to the point that the resistance is too high. You could prevent this by using AC, but then the circuit would be a lot more complicated. I would opt for capacitive sensors, Analog Devices have an interesting app note about Capacitive Liquid Sensors Or you can follow this Instructable

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  • \$\begingroup\$ I don't think AC will stop electrolysis but the corrosion must be the issue he's facing. \$\endgroup\$
    – Dorian
    Dec 27, 2018 at 10:04
  • \$\begingroup\$ @user156047 I too think you are right, but i dont understand anything about Capacitive liquid sensors. But, if i were to replace the contact points with something non-corrosive and have less chance for electrolysis would that work? \$\endgroup\$
    – Alex Robbin
    Dec 27, 2018 at 10:09
  • \$\begingroup\$ @AlexRobbin Maybe it would be better to use large electrodes. Not only the corrosion but also mud or particles attracted by the current flow might play a role in this. If you have large electrodes they will have a low impedance even covered with some impurities. \$\endgroup\$
    – Dorian
    Dec 27, 2018 at 10:35
  • \$\begingroup\$ For what I remember from my Uni days, there are two possible causes to corrosion, one is electrolysis and the other dissimilar metals. Electrolysis is the splitting of water cells, and that requires I believe 1.23V to happen. Unfortunately this means that for conducting the electricity you will only rely on the impurities of the water. I don't think it is a dissimilar metal issue due to the voltage you use. \$\endgroup\$
    – Elmesito
    Dec 27, 2018 at 10:44
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    \$\begingroup\$ You can easily check this by inspecting the probe wires, right? \$\endgroup\$
    – user253751
    Dec 27, 2018 at 11:54
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It's due to corrosion and electrolysis process mostly.

Go with some alternative thing like Float switche. Follow the link FLOAT SWITCH

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