Novice question re separate power supply

Sorry if this is a stupid question, but I'm a total beginner.

I understand (at least on a basic level) the notion that when using Arduino to drive a motor or other device which draws more current than the Arduino board can handle, it is necessary to use the Arduino to drive a relay or transistor, which in turn switches a separate circuit (driven by its own power supply) on and off. My question, is, just how isolated do the two power supplies (i.e., the one which powers the Arduino board and the one which powers the higher-current side of things) have to be? In particular, can I use a single 9V battery, with one positive lead going to the Arduino via the power jack and a separate positive lead (parallel to the one which powers the Arduino) going to the other side of the transistor or relay where the high current draw components are located? Or do I need to use two separate batteries? (Either way, as I understand it the negative leads (assuming I'm using negative ground) should be tied together).

Thanks.

Rob Rothman

One battery is one supply! Think about it, it can only have a particular voltage at any given time, and if the motor stomps that down on high current peaks you don't want the Arduino 5V falling as well.

Two batteries, or PSUs are needed. Grounds are common.

Small 9V batteries cannot power a motor, you need a supply capable of large currents, even small motors take 1A or so.

If you have a battery that can supply plenty of current it can be used to power the Arduino and other devices - as you say by taking a power wire from the battery to the Arduino and another from the battery to the other device(s).

It would probably be a good idea to use 2 separate power supplies during project development as problems due to low voltage often seem to be programming problems and waste a lot of time. When you know it works with separate power supplies then you can try it with a single supply.

...R

Thanks.

If I understand correctly, the potential problem with using a single battery with parallel hot leads is that the battery might not have enough juice to power both sides, as opposed to a concern that it might pull too much current through the Arduino board and fry some of its components. Is this correct?

Rob Rothman

RobRothman: If I understand correctly, the potential problem with using a single battery with parallel hot leads is that the battery might not have enough juice to power both sides, as opposed to a concern that it might pull too much current through the Arduino board and fry some of its components. Is this correct?

I'm being cautious in case of misunderstanding.

If you have a single power connection to an Arduino and then draw power for other devices (such as motors) from the Arduino board there is a high risk of overloading the circuits on the Arduino board. That will almost certainly cause the Arduino to reset giving rise to strange symptoms, and possibly damage to the Arduino.

If you draw power from a single source with one power line going to the Arduino and a separate power line going to the other devices you may still run into the problem of the Arduino resetting if the power source can't meet all the demand. However you will not be running the risk of overloading the Arduino circuits.

...R

My question, is, just how isolated do the two power supplies (i.e., the one which powers the Arduino board and the one which powers the higher-current side of things) have to be?

You can use Optocouplers (Optoisolators) both circuits will be completely separate and isolated

omersiar: You can use Optocouplers (Optoisolators) both circuits will be completely separate and isolated

Not relevant to the OP's question.

...R

Robin2:

omersiar:
You can use Optocouplers (Optoisolators) both circuits will be completely separate and isolated

Not relevant to the OP’s question.

…R

I was trying to make a Reference for others who reads this post

omersiar: I was trying to make a Reference for others who reads this post

Quite likely there is a gap in my knowledge but I am not aware that power can be passed through optocouplers so that two devices can share the same power supply - which is what the OP is enquiring about.

...R

RobRothman: Thanks.

If I understand correctly, the potential problem with using a single battery with parallel hot leads is that the battery might not have enough juice to power both sides, as opposed to a concern that it might pull too much current through the Arduino board and fry some of its components. Is this correct?

Rob Rothman

Sort of - the lead is at a single voltage, so if one side overloads the supply, both sides see the voltage drop. If you are to have two supplies it cannot be done with one supply and two leads!!!!

RobRothman: My question, is, just how isolated do the two power supplies (i.e., the one which powers the Arduino board and the one which powers the higher-current side of things) have to be?

Of course this is not a must to do, I am aware of this is not sharing same power supply I am talking about possibility I was trying to say its possible to have a circuit like this one: