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I'm just a hobbyist and actually from software side. Trying to build a simple water level indicator and found the following circuit using the IC ULN2003.

But due to my very less knowledge I'm not able to figure out the requirement of that since its straight forward without that IC

Here is the schematic I have got from a search

enter image description here

But its the same if we wire the following way, isnt it?

enter image description here

I'm not able to understand the purpose of that ULN2003 in this case, since in my schematic as well it does almost the same I though..

So what that IC really does in that circuit rather than just closing a circuit

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The current in the tank medium will be very low and will not be able to support the needed current required by the LED to glow.

The ULN2003 IC takes lower current and will be able to drive the LEDs by sing the power from VCC pin.
It is called a driver IC which consists of Darlington transistors to work at higher voltages and higher currents.

enter image description here

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  • \$\begingroup\$ thanks a lot man.. So since it takes the power from VCC directly LEDs getting the maximum current based on the VCC, isnt it? \$\endgroup\$ – Sandeep Thomas Mar 6 '20 at 11:27
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The ULN2003 here acts as a driver. It can draw up to 500 mA from VCC and each Darlington pair in ULN2003 can withstand up to 50 volts when circuit is open (or transistors are off). It is also an essential component when using inductive loads such as relays and inductors. Note that inductive loads produce back EMF ( electromotive force ) due to resisting to sudden current changes.

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