"Reverse" power flow in Arlo Power Supply
When I turn off the Arlo Power Supply, the 5 volt lines on the power supply continue to receive power.
It appears to me that the Activity Board is supplying power from the USB connection, through it's power "in" connection and that is making it out to the 5 volt line.
This seems dangerous to me. Is it really safe to run anything and everything on my 5 volt line from my computer's USB port via the ActivityBoard?
Is there a way to prevent this, either by modifying the Activity Board or the Arlo Power Supply?
I think someone else mentioned this before, but I couldn't find it or an answer.
Thank you.
It appears to me that the Activity Board is supplying power from the USB connection, through it's power "in" connection and that is making it out to the 5 volt line.
This seems dangerous to me. Is it really safe to run anything and everything on my 5 volt line from my computer's USB port via the ActivityBoard?
Is there a way to prevent this, either by modifying the Activity Board or the Arlo Power Supply?
I think someone else mentioned this before, but I couldn't find it or an answer.
Thank you.
Comments
The five-volt regulator in the Propeller Activity Board will let power from the board's internal five-volt power rail leak out through the barrel jack connector, which in your case is connected to the Power Distribution Board.
The connection between USB power and the five-volt rail on the Propeller Activity Board is heavily protected, so if there is a short or too much power draw, the Propeller Activity Board will disconnect the five-volt power rail from USB power, before it draws more current than the USB port has allotted it.
If you would like to completely prevent the Propeller Activity Board from drawing any USB power, under any conditions, you can either connect it through a non-powered USB hub, or you can change a few EEPROM settings within the FT231X USB-to-serial converter. If you'd like to do the latter, let me know and I'll write up the instructions.
David Carrier
Parallax Inc.
That is very good to know!
Yes, I would like to know, please send me the instructions. Thank you!
As I mentioned here, when the Arlo Power Distribution Board is off but connected to the PAB, my USB current meter said the PAB drew 650mA of current. I'm sure most of this current was being pulled from the Arlo Power Distribution Board.
I personally think the Arlo Power Distribution Board's design should be changed to prevent this. If someone were to leave their robot connected to a PC for an extended period, the continuous 650mA current may be enough to damage the PC. I know I personally leave Propeller boards connected to my PC via USB for days at a time.
Here are the instructions to change the Propeller Activity Board USB powering settings using a Windows computer:
If you disable powering from a computer's USB port, you will have to power the board separately while programming the Propeller microcontroller. To bring the board back to its original settings, Do the same, but set C0 to 'BCD_Charger#' and C1 to 'PWREN#'.
— David Carrier
Parallax Inc.
Thanks David and Duane and thanks for the great question ChrisL8!
We're in the middle of developing a "Building a full-blown Arlo Tutorial" for the Learn site. I shall include this in it as well.
Hey Duane, have you tried this yet?
-MattG
Turning off the USB power?
No. I added a switch between the APDB and the PAB. I like being able to power the PAB from USB while I'm programming the board.
I had to think a bit why I wanted the USB power but I finally came up with the reason. While I'm working on the program at the bench, I often have the robot's battery on the charger (I'm using an ELEV-8 LiPo) so it's convenient to power the PAB from USB.
The present arrangement (of using a switch between PAB and APDB) doesn't bother me but I'm concerned about others who may not be aware the APDB can be pulling a lot of current from the USB via the PAB. I had one of those USB meters erco told us about on my USB port so I saw the 650mA draw. I doubt many other users of the APDB have a meter on their USB port.
As I think about this a bit more, I'm not sure the APDB should be changed but I think there should be some sort of warning about the power flow issue included in the documentation.