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Hi,

Had a bit of a search around but still a bit confused on this point.

I've got a project where the arduino is powered by USB from another device, which in turn takes its power from a 5v voltage regulator, connected to a battery pack.

My question is relating to grounding, and avoiding running too much current through the arduino's ground pins.

If i have my grounds linked (there is a wire connecting the arduino ground pin and the negative side of the battery PRE regulator) do I need to worry about too much current flowing through my arduino's ground pin

I have a few MOSFET controlled higher power LEDs etc which will take 100mA each. The intention is that the current will flow from the regulator, through these devices, through the MOSFET gate and down to ground of the battery, without ever passing through the arduino itself.

Will this happen? Does linking the ground to the negative achieve this? Thanks in advance!
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If i have my grounds linked (there is a wire connecting the arduino ground pin and the negative side of the battery PRE regulator) do I need to worry about too much current flowing through my arduino's ground pin

I have a few MOSFET controlled higher power LEDs etc which will take 100mA each. The intention is that the current will flow from the regulator, through these devices, through the MOSFET gate and down to ground of the battery, without ever passing through the arduino itself.

Will this happen? Does linking the ground to the negative achieve this? Thanks in advance!

Yes, under normal circumstances the current is going to take the most direct pathway available to the lowest voltage in the circuit.  Now in some situations a reverse current is possible, but that's usually due to either something going very wrong in your circuit (e.g. a part failing or a combination of shorts) or outside factors like a current induced by a very strong external electromagnetic field.  A diode between the Arduino's ground loop and the negative terminal of the battery will offer some protection from the latter by blocking any reverse currents large enough to potentially damage an Arduino that are induced in the rest of the circuit.
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Hi,

Had a bit of a search around but still a bit confused on this point.

I've got a project where the arduino is powered by USB from another device, which in turn takes its power from a 5v voltage regulator, connected to a battery pack.

My question is relating to grounding, and avoiding running too much current through the arduino's ground pins.

If i have my grounds linked (there is a wire connecting the arduino ground pin and the negative side of the battery PRE regulator) do I need to worry about too much current flowing through my arduino's ground pin

I have a few MOSFET controlled higher power LEDs etc which will take 100mA each. The intention is that the current will flow from the regulator, through these devices, through the MOSFET gate and down to ground of the battery, without ever passing through the arduino itself.

Will this happen? Does linking the ground to the negative achieve this? Thanks in advance!

Sounds like you are doing it correctly, but maybe redundantly so. The Arduino must have a common ground reference from the voltage source, and as you stated your Arduino is being powered via it's USB connector, and if that is a fact, then it will already have a ground reference established via the USB as that connector carries both +5vdc and a ground connection, as well as two data signal lines.
You external higher current drawing components (like your mosfet controlled LEDs) are best served if they have a dedicated ground reference wire to the voltage source, the battery in your case. That keeps higher ground return currents out of the arduino board and can help with noise suppression.

I see no advantage, only problems, with adding a diode in any of the ground leads as the prior poster suggested. Perhaps if he supplied a schematic drawing his idea might be better understood?

Lefty
« Last Edit: September 20, 2012, 12:04:37 pm by retrolefty » Logged

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Thanks for the replies.

As for the redundancy, the arduino is being used to measure (via a resistor voltage divider) the voltage of the battery pack (usually 11.2v) BEFORE the regulator, as measuring it after the regulator would give me no change as the voltage dropped (due to the arduino reference dropping with it) .

This monitoring didn't work until i linked the negative term on the battery to the arduino's ground - hence the reason for what may seem like a redundant connection.

If it makes more sense, I have 11.2v of battery power, running (via the regulator) a raspberry pi, which is running the arduino.

Sounds like i'll be safe, i imagine any currents heading to ground will take the direct path to the battery pack, rather than going through the arduino -> usb connection -> pi -> voltage regulator -> battery.
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Thanks for the replies.

As for the redundancy, the arduino is being used to measure (via a resistor voltage divider) the voltage of the battery pack (usually 11.2v) BEFORE the regulator, as measuring it after the regulator would give me no change as the voltage dropped (due to the arduino reference dropping with it) .

This monitoring didn't work until i linked the negative term on the battery to the arduino's ground - hence the reason for what may seem like a redundant connection.

If it makes more sense, I have 11.2v of battery power, running (via the regulator) a raspberry pi, which is running the arduino.

Sounds like i'll be safe, i imagine any currents heading to ground will take the direct path to the battery pack, rather than going through the arduino -> usb connection -> pi -> voltage regulator -> battery.

I would have to review a schematic drawing of at least the complete power circuitry from battery to the various modules. Not sure why you needed to add a 'redundant' ground wire from the voltage divider/battery ground to the arduino for it to measure. The fact that the arduino was running at all means it had both good +5vdc and ground return to the regulator's output via the USB connection and the regulator's ground has to come from the battery ground, so who knows? A schematic drawing is worth a thousand posted words, so most likely we will not know the true answer unless you draw it out as built.

Lefty
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I've attached a rubbish schematic that i threw together in paint.

Until i added the wire in green, the voltage reading on the arduino pin fluctuated wildly around and made no sense.


* rubbish schematic.png (47.64 KB, 1366x791 - viewed 19 times.)
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I've attached a rubbish schematic that i threw together in paint.

Until i added the wire in green, the voltage reading on the arduino pin fluctuated wildly around and made no sense.

Well you are missing the key element of how the arduino was being wired for power and ground before you added the green wire. You stated it was coming via a USB connection via the external 5vdc regulator. Can you add that detail?

The ground path from the battery via black wire to regulator to pi to arduino via usb cable should have established a working ground reference, otherwise the arduino would have been able to run at all before you ran the extra ground? So I'm still confused, but it's probably not your fault.  smiley-wink

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« Last Edit: September 20, 2012, 01:04:28 pm by retrolefty » Logged

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Sorry if i've been unclear -

The arduino is being powered via its USB connection to the raspberry Pi. The Pi is being powered directly from the 5v regulator, which is a UBEC type.

The wavey blue line was supposed to indicate that!
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Sorry if i've been unclear -

The arduino is being powered via its USB connection to the raspberry Pi. The Pi is being powered directly from the 5v regulator, which is a UBEC type.

The wavey blue line was supposed to indicate that!


Again I have no explanation of why you had to add the additional ground wire, if the arduino was working at all before adding it.
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Well, mysteries exist I suppose.

Thanks for your help anyway, i'll leave the enchanted wire in and go back to troubleshooting if something lets smoke out!

Cheers
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Sorry if i've been unclear -

The arduino is being powered via its USB connection to the raspberry Pi. The Pi is being powered directly from the 5v regulator, which is a UBEC type.

The wavey blue line was supposed to indicate that!


Again I have no explanation of why you had to add the additional ground wire, if the arduino was working at all before adding it.

I do - the 5V regulator might be a DC->DC converter, these usually have isolation between input and output.
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I do - the 5V regulator might be a DC->DC converter, these usually have isolation between input and output.

If so that would explain the need to directly ground the Arduino, thanks for the insight MarkT.
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I do - the 5V regulator might be a DC->DC converter, these usually have isolation between input and output.

Aye it is. Thanks a bunch!
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