What all things are required for using arduino as a switch to control water pump

Other Hardware Motors, Mechanics, Power and CNC
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So i have a project and i am a very very big newbie at this so i need your help. I have a arduino uno and in that i want to use that as a switch to control my 4 water pumps and they require 3-6v. All i know so far is that i can not power them all for that single arduino so i will use my variable power supply to control them (i think that i will control them in series if i am wrong please tell) and then i want the arduino to supply the power when my phone bluetooth will send signal to the bluetooth module of arduino and it will select which motor to supply power to.

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Use the forum Google search function in the upper right of this page to search for "arduino relay" and similar key words. You will probably find many previous project discussions and code using these devices.

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You just need to use: Arduino + Relay + water pump and BlueTooth module. You can refer to Arduino - Relay tutorial

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DyfedPugh:
OT, but referring to that tutorial: although it might be uncommon to do so, there's no reason why the switched voltage can't be lower than the controller's:

I think we still need a relay because the power supply for water pump may be "high-current", even it is low-voltage

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@DyfedPugh, Thank you for valuable recommendation.

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Sanketsavani:
So i have a project and i am a very very big newbie at this so i need your help. I have a arduino uno and in that i want to use that as a switch to control my 4 water pumps and they require 3-6v.

You need to tell us exactly what water pumps these are. A link to the datasheet is ideal, a link to a product page will do.

All i know so far is that i can not power them all for that single arduino so i will use my variable power supply to control them (i think that i will control them in series if i am wrong please tell)

Almost certainly not. Motors are not constant loads so will not share voltage equally.

and then i want the arduino to supply the power when my phone bluetooth will send signal to the bluetooth module of arduino and it will select which motor to supply power to.

For 3 to 6V a set of MOSFETs can be used to switch - but we have to know the stall current rating of the pumps,
and there will need to be free-wheel diodes to protect from kickback.