itsalljustaride
Posts: 6
Joined: Tue Oct 17, 2017 2:33 pm

Display Hit or Miss At Power On When Using External Power Supply

Tue Oct 17, 2017 2:39 pm

Hello,

I have run into an intermittent issue with the 7" RPi screen whereby the unit will sometimes not be recognized at startup if it is powered using the micro-usb and both the Pi and the Screen are powered on at the same moment (ie if power supply has on/off for both). I assume this is because the screen may take a second or so to fully power on perhaps? And in the interim it goes unrecognized by the Pi?

I have tried setting a boot_delay of up to 8 seconds in the config, but that only seems to have made it a little less often, but hasn't eliminated it completely.

The problem goes away if I power the unit via the GPIO, but my setup makes this less than optimal due to power needs.

Appreciate any advice. Thanks.

alphanumeric
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Joined: Tue Jan 19, 2016 2:17 pm
Location: Sydney, Nova Scotia, Canada

Re: Display Hit or Miss At Power On When Using External Power Supply

Wed Nov 01, 2017 12:31 pm

I run my Pi and Pi Foundation Screen from the same power source. No on off switch, I just plug it in. No such issue here. Mine is 5V 10A Power supply. What is the max current rating of your supply?

itsalljustaride
Posts: 6
Joined: Tue Oct 17, 2017 2:33 pm

Re: Display Hit or Miss At Power On When Using External Power Supply

Wed Nov 01, 2017 4:25 pm

The supply is a combo USB and AC outlet (I'm using the USB port), like such:

https://www.amazon.com/gp/product/B01N0 ... UTF8&psc=1

Lists specs as "USB Electrical Parameter: DC 5V, 1.0 AMP"

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Burngate
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Re: Display Hit or Miss At Power On When Using External Power Supply

Wed Nov 01, 2017 5:25 pm

The screen takes 400mA according to https://www.raspberrypi.org/documentati ... /README.md so a 1A psu isn't going to be able to cope, particularly at power-on when both Pi & screen are going to demand extra current.

itsalljustaride
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Joined: Tue Oct 17, 2017 2:33 pm

Re: Display Hit or Miss At Power On When Using External Power Supply

Wed Nov 01, 2017 5:53 pm

If the display is being powered separately shouldn't 1A be more than enough for 400mA? The Pi is on the regular wall-wart 2.5amp PSU.

alphanumeric
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Joined: Tue Jan 19, 2016 2:17 pm
Location: Sydney, Nova Scotia, Canada

Re: Display Hit or Miss At Power On When Using External Power Supply

Wed Nov 01, 2017 7:15 pm

The way the first post is worded, it sounded to me like they were both powered by the same power supply. I see what your doing now. The one connected to the screen must be taking longer to turn on? I don't have a definite answer for you though, other than you need a better arrangement. Two official Pi power packs plugged into a power bare that has an on off switch should work OK. One powering the Pi and one powering the display.

itsalljustaride
Posts: 6
Joined: Tue Oct 17, 2017 2:33 pm

Re: Display Hit or Miss At Power On When Using External Power Supply

Wed Nov 01, 2017 8:21 pm

I'm considering switching out the 2.5A Pi plug, getting a 3.0 or 3.5A one, and going back to powering both the Pi and the Screen via one connection over GPIO.

Any thoughts on these?:

https://www.amazon.com/Raspberry-Micro- ... +micro+usb

https://www.amazon.com/dp/B01N336XEU/re ... 67661&sr=1

Thanks.

alphanumeric
Posts: 1257
Joined: Tue Jan 19, 2016 2:17 pm
Location: Sydney, Nova Scotia, Canada

Re: Display Hit or Miss At Power On When Using External Power Supply

Thu Nov 02, 2017 9:02 am

Instead of using the GPIO for power you could use something like this, https://shop.pimoroni.com/products/spli ... wer-cable It's basically what I'm doing now, except I made my own cable.

itsalljustaride
Posts: 6
Joined: Tue Oct 17, 2017 2:33 pm

Re: Display Hit or Miss At Power On When Using External Power Supply

Mon Nov 13, 2017 4:11 pm

As an update to this, I bought the PWR+ 3.5A unit, and saw no improvement with display powered from GPIO. I even removed some LEDs I had hooked up to the GPIO and was still getting low-power indicator icon on the display unit. Gonna try the Y-cable solution.

alphanumeric
Posts: 1257
Joined: Tue Jan 19, 2016 2:17 pm
Location: Sydney, Nova Scotia, Canada

Re: Display Hit or Miss At Power On When Using External Power Supply

Mon Nov 13, 2017 5:36 pm

I do believe if you power via the Pi's GPIO that's after the poly fuse? I can't remember what that's restricted too though current wise?

itsalljustaride
Posts: 6
Joined: Tue Oct 17, 2017 2:33 pm

Re: Display Hit or Miss At Power On When Using External Power Supply

Mon Nov 20, 2017 3:54 pm

*Update* I tried the splitter on both the PWR+ 3.5 amp brick and the other original 2.5 amp one from Canakit.

Oddly, PWR+ brick still showed low power warning icon every few seconds.

Canakit works fine after boot, but does show low-power once during bootup. After full boot it's fine though.

Weeeeird...

alphanumeric
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Joined: Tue Jan 19, 2016 2:17 pm
Location: Sydney, Nova Scotia, Canada

Re: Display Hit or Miss At Power On When Using External Power Supply

Mon Nov 20, 2017 8:08 pm

The lightning bolt flashing indicates a low voltage condition. Below 4.65 volts I believe. High current draw though thin gauge wire will result in a voltage drop across the power cord. Some Pi power supplies are rated at 5.1 or 5.2 Volts to counter act this. And have nice tick beefy wires.

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