XU4Q how to stop red LED sooner on power off

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oddulf
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XU4Q how to stop red LED sooner on power off

Post by oddulf »

Hi,

Short version: How do you stop the red LED on the Odroid XU4Q sooner on a shutdown?

Long version:
I'm testing an Odroid XU4Q to possibly replace a less future proof C1+ in a remote headless installation powered by a UPS. No HDMI cable attached.

I have noticed a big difference to the Odroid C1+ in how soon a "power-up event" from the UPS will boot the XU4Q. A shutdown C1+ will display a red LED until the UPS cuts power, then reboot if the UPS is switched on again after a few seconds; a shutdown XU4Q, however, will somehow retain charge and its red LED is only disappearing about 97 seconds after the UPS cuts power - before those 97 seconds have elapsed, a power-up event will NOT boot the XU4Q.

Removing the barrel DC connector or pressing the on/off switch will dissipate the power quickly and shut down the red LED; unfortunately, neither option is available for a remote installation.

Is this to enable the handy on/off switch? It is useless for remote power cycling, as the XU4Q won't start again after the UPS 5 second power-off window. I am thinking about hacking it with an RTC wake call, but it would be much cleaner and more robust if there were a possibility to dissipate the charge immediately on a power loss just like the C1+. Any handy pin solutions?

I have seen a possibly related solution on youtube connecting pins 1 and 12 over an electrolytic capacitor of 4.7 uF; but again, it seems to require a manual connection and disconnection on site - would there be a software solution disconnect this on boot and connect on shutdown?

Would the fan of the XU4 help dissipate the power quicker?

Many thanks for your help!

Tomas J.
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Re: XU4Q how to stop red LED sooner on power off

Post by Tomas J. »

I think simplest option would be connect discharge resistor (something like 47Ohm 1W) to DC supply lead.

oddulf
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Re: XU4Q how to stop red LED sooner on power off

Post by oddulf »

Thank you, Tomas, that's really useful!

I'll give that a go in the next few weeks and report back.

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Re: XU4Q how to stop red LED sooner on power off

Post by phaseshifter »

470 ohm is too little resistance you will be loading up the power supply..
and could smoke the resistor up. not to mention the latter..
.i would try with a 4.7 k at first..then you could go lower3.9k using increments
better to start with a higher resistance first

470 ohm is to smaller amount to be connected perminatley on the power rail // across the power rail...

you will also create a voltage drop on the power rail and could stop the board... if it is to lower resistance..

once you fit the resistor monitor pin one of the 30 pin header see that you have not created a amount of voltage drop
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oddulf
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Re: XU4Q how to stop red LED sooner on power off

Post by oddulf »

Thank you,

yes I was worried about the effect on voltage reaching the odroid. I know very little, but could one fit the resistor between two of the 30 pins instead of cutting the incoming power lead?

I am curious what the design advantage this delay of power dissipation has - is it to enable the on/off switch? Or is it a design fault?

phaseshifter
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Re: XU4Q how to stop red LED sooner on power off

Post by phaseshifter »

the C-2 is a different matter...it is configured differently...

generally with the XU-4 the only time the red led will go out is when the power supply is unplugged or turned off from the mains,,,the red led is like a "power good" indicator..it also acts as a system good led..this is to say that the red led is draining the surplus current held in the power supply filter capacitors...if you cut the power to the board .. hard switch it ...then the red led will go out straight away...

as for putting the resistor on the pins of the 30 pin header..it can be done this way and you may find that placing it there it would be dissipating the current that is still in the board.quickly when the power is cut but would be creating the highest voltage drop..not a good idea.. .that is to say

there may be a wiki page on how to turn it off,,....but from mem the wiki page only refers to the blue led..the red led is hardware driven so to speak..


..===>>powersupply==>>board circuitry==>>>4.7k load...so it would only dimm it quicker once the power supply has been removed.

it will only drain the current left in the board after the input power==>>power plug..is removed or the mains switched off... hence while the power supply is plugged in and the mains is turned on ..you cannot turn the red led off..

if you want to turn the red led off and or dimm it by using the resistor .constantly .you would have too much voltage drop rendering the board not to function and could damage the board.if it`s resistance is to low..it will cause a short circuit across the board`s circuitry ..most likely. depending on it`s resistance...


so after all that i have said it really needs to be placed on the barrel jack..it can be done there.. but is messy and it would require soldering it to the under side of the board where the barrel jack is mounted...

also you would also have to consider the wattage of the resistor.
. most prolly need to be a 5 watt device...a 1 watt may suffice..soz i have not done the math..

.as it is gong to be there "perminatley " it will incur a voltage drop constantly...which may not be feasible at all...

what you want to do ..really i would not recommend it..
Last edited by phaseshifter on Sun Mar 31, 2019 8:13 am, edited 1 time in total.
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phaseshifter
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Re: XU4Q how to stop red LED sooner on power off

Post by phaseshifter »

I am curious what the design advantage this delay of power dissipation has - is it to enable the on/off switch? Or is it a design fault?
where did you get this information...????

as i spoke earlier..the red led remains lit due to the filter capacitors holding ripple filtering current..if you unplug or hard switch the power 5 volt rail after shutting down the board it will go out instantly...

https://wiki.odroid.com/odroid-xu4/appl ... ed_control

above is the xu4 wiki page notes..
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oddulf
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Re: XU4Q how to stop red LED sooner on power off

Post by oddulf »

Thank you, phaseshifter, for very thorough information!
I am curious what the design advantage this delay of power dissipation has - is it to enable the on/off switch? Or is it a design fault?

where did you get this information...????
... it was entirely my own conjecture - as you can tell by now, I'm not very experienced with electronics...
..if you cut the power to the board .. hard switch it ...then the red led will go out straight away...
Correct me if I'm wrong, but my problem is that is doesn't go out straight away - it stays on, stopping a subsequent power-up event to boot it. Do you think I might have a faulty board?? I thought it is a design difference between the C1+ and the XU4Q?

I have read the wiki-page and I agree it is not applicable to this problem.

Many thanks!

Tomas J.
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Re: XU4Q how to stop red LED sooner on power off

Post by Tomas J. »

phaseshifter wrote:
Sun Mar 31, 2019 2:19 am
470 ohm is too little resistance you will be loading up the power supply..
P=U^2/R P=5^2/47=0.53W

oddulf
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Re: XU4Q how to stop red LED sooner on power off

Post by oddulf »

Update: Almost two years later, we discovered that the red light does indeed dissipate very quickly on a hard power cycle - the problem I described above only occurs if the odroid is gradefully shutdown before the power is disconnected from the PSU.

Having corruption-proofed our odroids to the limits of the official ubuntu 18.04 image (read-only rootfs etc), we have chosen to accept the risk of eMMC card corruption and switched off the UPS graceful shutdown script. So far, we have seen a few hundred hard power cycles without corruption.
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