Daveawalker
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HDMI earth /spike causing sd card corruption??

Tue Oct 10, 2017 2:16 pm

We use lots of Model As 24/7 monitoring a nurse call system in hospitals.
At some locations we have random sd card corruptions. Its really difficult to know if power goes down or not but suddenly the pis will show the boot screen. As they are running on the hospital ups there should not be spikes.. We've tried grounding the TVs, which or may or may not have made a difference as we still randomly get problems. Certain locations in hospitals are worse than others.
Any ideas on cause/remedy?

wally333
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Re: HDMI earth /spike causing sd card corruption??

Tue Oct 10, 2017 3:19 pm

If you are powering the Pi from the normal "wall wart" power supply the pi should be "floating" with respect to earth and A/C mains. This may or may not be desirable depending on the rest of your system wiring connected to the Pi.

I'd look to what else is plugged into the Pi. As a general rule you only want "earth" ground connected to system ground at one point, but this is usually easier said than done in the real world.

I've had problems with transients from thunderstorms and my Beaglebone (it has hundreds of feet of external interface wiring connected), seems much improved once I figured out what was creating the "ground loop" -- it was a video camera power supply that was on a different AC breaker that "connected" the Beaglebone "ground" to the Video security system ground via the Eterhnet cable connection. Getting everything on the same AC mains breaker seems to have fixed the issue -- we've has many heavy thunderstorms since I first noticed the problem and finally implemented what appears to be the solution.

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Burngate
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Re: HDMI earth /spike causing sd card corruption??

Tue Oct 10, 2017 4:37 pm

Daveawalker wrote:
Tue Oct 10, 2017 2:16 pm
... As they are running on the hospital ups there should not be spikes...
The ups might isolate the hospital from outside problems, but I would expect things such as MRI scanners to put noise on the internal system.

As wally333 says, the Pi is normally floating, and most modern TVs also.
Connecting either to "earth" could cause them to have various noisy signals induced into them, depending on your definition of "earth".
The "protective earth" connection on a standard domestic-style socket is merely a piece of wire that, at some point in the system, is connected to a metal stake buried in the ground (probably at the UPS)
The wires themselves can act as aerials for all sorts of nasties.

Are the Pis interconnected, and if so how? Wired network? I would guess not, since the A doesn't have a built-in network port.
I would look into galvanically isolating them, if possible.

Just out of interest, one site I worked had video equipment in two areas about 100m apart, with baseband SDI video signals going between the two. Same UPS, same "earth", but the signals were unusable because of a couple of volts at 50Hz on them. Expensive in-line video transformers, isolating the grounds, cured it.

rln
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Re: HDMI earth /spike causing sd card corruption??

Thu Oct 19, 2017 9:23 am

Does same issue occur if you disconnect the TV? (Watch the system uptime to detect reboots.)
Author of the robust Nard distro http://www.nard.se

steveb4pi
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Re: HDMI earth /spike causing sd card corruption??

Sun Oct 22, 2017 9:47 am

A power 'glitch (or low-voltage at the Pi) will often result in a reboot, however, 9 times out of 10 the SD card will be just fine .. (actually, after hundreds of times of just pulling the power-plug, I would even say 99 times out of 100 it's just fine)

So, when you see the Pi reboot, if it ALWAYS 'fails' (and you see some Error report of a corrupted files), it's likley not a 'power glitch' ...

Unfortunatly, "SD corruption" can be caused by many things, including software that keps writing to the card (and thus 'wearing it out')

If possible, you could try swapping out the A+ for a Pi Zero (it has twice the RAM of an A+ so les likley to need 'virtual memory' for anything) .. however it lacks the 'touch screen ribbon connector socket == so maybe you can't use it ..

If you are the programmer, you could look at minimisong any 'writes' to the SD card (i.e. use tmpfs, or use a Pi operating system that doesn't kill the SD card by using 'virtual memory') - the fewer 'writes' the less likley a power glitch (if that's what it is) will hit the Pi during a SD 'write' operation and thus cause corruption ..

Daveawalker
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Re: HDMI earth /spike causing sd card corruption??

Mon Oct 23, 2017 2:59 pm

The problem is we have over 100 units out here and only 3 or 4 have problems and they are not at the same site. A site may have 10 units and 2 have issues. It is therefore not software!

The original pis ie model A had protection diodes on the HDMI , we can t seem to find if the ModelA+ also have these diodes. Model A does not have this problem- pity we cant get some more of them .

"Does same issue occur if you disconnect the TV? (Watch the system uptime to detect reboots.)" sorry cant do that it's a live system which has a problem maybe once a week /month

rln
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Re: HDMI earth /spike causing sd card corruption??

Mon Oct 23, 2017 5:12 pm

Daveawalker wrote:
Mon Oct 23, 2017 2:59 pm
sorry cant do that it's a live system which has a problem maybe once a week /month
No problem, just send another Pi to same location. Let one of them be connected to a TV but let both run same software and get power from same wall outlet.
Author of the robust Nard distro http://www.nard.se

Daveawalker
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Re: HDMI earth /spike causing sd card corruption??

Tue Oct 24, 2017 5:34 am

Except then you bring new power issues into the equation. I guess a complete spare system may be an option.. but how do we know if it's rebooted without the screen.. Site is 700km away..

rln
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Re: HDMI earth /spike causing sd card corruption??

Tue Oct 24, 2017 9:25 am

Can you monitor the system remotely somehow via WiFi, VPN, SSH etc? If not; install a complete spare system (except for TV) and attach a GPRS modem to it. Then you can SSH to it from remote and check system uptime, logs etc.
Author of the robust Nard distro http://www.nard.se

Daveawalker
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Re: HDMI earth /spike causing sd card corruption??

Tue Oct 24, 2017 9:47 am

Except that we presume that the issue is caused by HDMI spikes so how would leaving a TV off help.

rln
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Re: HDMI earth /spike causing sd card corruption??

Tue Oct 24, 2017 9:55 am

You presume it is the hdmi, but do you really know it? If you are so sure about the hdmi, then replace the TV with a better one...
Author of the robust Nard distro http://www.nard.se

Daveawalker
Posts: 21
Joined: Fri Apr 26, 2013 3:26 pm

Re: HDMI earth /spike causing sd card corruption??

Tue Oct 24, 2017 10:05 am

On 1 site we have say 20 tvs all the same,only 1 floor has an issue. On that floor we have a different unit that is a logger with no tv and it does not have a problem, it has internet access for emailing and I can see it is not rebooting.. I get an email every time it reboots... If it were power then all three would have a problem as each floor has its own power source.

rln
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Re: HDMI earth /spike causing sd card corruption??

Tue Oct 24, 2017 10:44 am

So if only some TVs cause problems; replace them.
Author of the robust Nard distro http://www.nard.se

Daveawalker
Posts: 21
Joined: Fri Apr 26, 2013 3:26 pm

Re: HDMI earth /spike causing sd card corruption??

Thu Nov 02, 2017 3:17 pm

Ok we managed to get a faulty set up back..
Pi boots up leds show that.
But no hdmi output from Pi . Hdmi cable does not work and monitor does not detect hdmi with a working cable..
Power drawn by Pi3 is much higher than normal
Some serious spike ? or ??

Ovitzik
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Joined: Tue Jan 30, 2018 6:48 pm

Re: HDMI earth /spike causing sd card corruption??

Tue Jan 30, 2018 7:05 pm

Hi.
I want to make a Nurse Cal System wit Raspberry Pi 3.
I want to make some this:
15 input (push Butoons)
touchscreen 7''
USB 16 relayboard for output-15 rellay for 15 rooms ,1 relay for allarm.
On the touchscreen monitor i try to configure like in picture with CDP but i dont know how make link between Rooms and rellays from rellayboard.
Nurse call.jpg
Nurse call.jpg (107.61 KiB) Viewed 2253 times
Mute for deactivate allarm and Confirmare for ack. room wich is triggered.
Can anybody help me?

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