I am making a project on water level indicator. I've completed the circuit like this:

enter image description here

The circuit is closed through the water.

The problem is even before switching on the circuit, and with terminals not immersed in water, LED glows feebly when connected across 5 VDC source powered from AC source, but not with a 9 V battery.

I want to use the circuit powered from AC, for a long run. I want to know where I am going wrong.

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    \$\begingroup\$ Please show us a schematic indicating all relevant connections. A text dump listing components is not a schematic. \$\endgroup\$ – ζ-- Nov 7 '18 at 15:13
  • \$\begingroup\$ Include details (schematic?) of your AC-sourced DC supply. \$\endgroup\$ – mike65535 Nov 7 '18 at 15:25
  • \$\begingroup\$ I have added the schematic above. \$\endgroup\$ – sumathi prasad Nov 7 '18 at 15:36
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    \$\begingroup\$ "Circuit is closed through water" is this a specific type of water? Water can have a wide range of resistivity depending on the conditions and what is dissolved in it. You almost certainly do not want to run your LED current through the water you are trying to detect. \$\endgroup\$ – Chris Fernandez Nov 7 '18 at 16:38
  • \$\begingroup\$ These things happen even before immersing sensors in water. \$\endgroup\$ – sumathi prasad Nov 7 '18 at 16:47

Your 9V source is coming from something (probably a switchmode AC adapter) that has some "leakage" from the mains to ground.

You can likely solve this by grounding (to earth) one side (usually the minus side) of the adapter DC output. This is also an improvement from a safety point of view, especially if your AC adapter is dodgy. Since water is involved it becomes even more important.


simulate this circuit – Schematic created using CircuitLab

Typically there is a "Y" safety capacitor from the mains to the output inside the AC adapter which causes some current to flow.

  • \$\begingroup\$ The AC plug has only two pins. \$\endgroup\$ – sumathi prasad Nov 7 '18 at 16:50
  • \$\begingroup\$ Exactly, that's why you're having the problem. It might go away if you turn the plug around, if that's possible. Or not. \$\endgroup\$ – Spehro Pefhany Nov 7 '18 at 16:51
  • \$\begingroup\$ OK I'll try this Sir and thank you for sparing your valuable time for me. \$\endgroup\$ – sumathi prasad Nov 7 '18 at 17:05

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