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RAMPS + ATX best practice

Posted by BackEMF 
RAMPS + ATX best practice
August 23, 2014 10:02PM
I'm playing with RAMPS and ATX and i notice a small cosmetic oddity

The situation is as follows:
D1 is removed from ramps.
I have a led to indicate the Standby state.
But when connected as described in the RAMPS wiki. Then there is voltage coming trough USB toward the Standby LED that makes the Led come ON even when the ATX PSU is NOT connected to the mains.

I know I could use a diode, but that would cause a voltage drop for one.

But my actual question is: Is this the correct behaviour?

Ramps WiKi tells me: The VCC pin can be connected to your ATX's 5Vsb to continuously power the Arduino from your ATX power supply. You will want to make sure that D1 is not installed or cut out.

All of this is what I have done. Thing is that I was not expecting voltage from USB to flow into the ATX. Should I just add A 1N4007 diode to block the 5V coming from RAMPS or is there a nicer way to do get around this?

EDIT: minor markup fix to the text.

Edited 1 time(s). Last edit at 08/23/2014 10:03PM by BackEMF.
Re: RAMPS + ATX best practice
August 23, 2014 10:27PM
The Arduino 5V supply will be powered from USB. That 5V supply is the same supply that runs all the 5V components on RAMPS.

The only way around this is to unplug the ATX supply.

Note: The USB port on your PC should handle the fact that the USB device already has it's own power. At least, the specs say stuff about it, so unless the PC doesn't follow the USB spec (and hey, some don't) then it shouldn't be a problem.
Re: RAMPS + ATX best practice
August 23, 2014 11:37PM
Hi Cefiar,

Thing is that it doen't seem electrically correct that current is flowing from USB to the ATX standby.
It's just a minor detail, i can add a Diode in the path. I just din't expect that voltage coming in from there, its not a UBS spec issue.

But ok VCC is VCC so it looks like this is by design.
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