Also powering the 8" HDMI screen


#1

Similar to another thread, but I have a different problem: I can’t get the thing going at all.

It all looks wired up just fine, but when I plug in the USB power (USB port, powered USB hub, whatever) I can’t seem to get a picture. The screen will briefly flick on blue, then disappear. The power light on the buttons bar will be red.

If I press the power button it briefly goes green (then straight back to red) and the screen itself will again briefly come on blue then flick off again.

not enough power? too much power? cabled up incorrectly?


#2

I’ve got the same issue - when plugged into a Pi 2 the power seems to keep dropping out. It works fine on a USB battery pack though, in the “DC 5V 2.1A” slot.

I can’t get any display from the Pi either, but I suspect that’s just a config file issue. It displays the HDMI output from my laptop fine.

Any ideas? Is it really supposed to be powerable from the Pi…?


#3

Heya! Yes it will power fine from the Pi (assuming it’s a Pi 2 or B+ at least!).

You must use a good quality 2A power supply such as the official Raspberry Pi Power Supply that is here: https://shop.pimoroni.com/products/raspberry-pi-universal-power-supply

You also need to make sure you configure forced HDMI output in config.txt (as the screen is powered from the Pi it starts up after the Pi performs HDMI detection so isn’t found by default).

In /boot/config.txt either add or un-comment the following line:

hdmi_force_hotplug=1

And you should be up and running!


#4

Cheers Jon.
Could I power both my Pi and the HDMI screen from one of your PiHubs?

(edit: dug out a PiHub I forgot I bought my wife a couple of years ago, and can confirm I can power it successfully from the PiHub. result!)


#5

Cheers Jon. I’ve done some more testing, and it sort of works - with the hdmi_force_hotplug and just the screen and the Picade board connected to the USB ports on the Pi 2 it will boot and display correctly. However, if I throw a wifi dongle into the mix it appears to work initially but after a while too much power seems to be drawn - the screen flashes off and then back on every couple of seconds and at the same time the LED on the Picade board also flashes off and then on. Removing the dongle stops that happening, putting it back in again starts the screen powering off and on again. Tried with the official Pi 2A adapter and a Blackberry Playbook adapter (I have a few as they’re very good for Pis and dirt cheap!).

I think a powered hub will solve the problem though, but it’s slightly disappointing - I was hoping for a completely clean solution, but I need wifi…


#6

Ahah, from a bit of reading around it seems that the B+ and 2 have a (raiseable) limit on the power draw from the USB ports of 600 mA after which it’ll cut off current and restart the bus (I think!), which would fit with the screen and the Picade board keeping turning off. At a guess the screen is using at least a couple of hundred mA, the Picade board (which is a Kickstarter one, so perhaps not fully optimised) is running an amp so probably quite power hungry too - I can believe that the Wifi dongle could pop it over the limit.

Apparently setting max_usb_current=1 in config.txt raises this limit to 1.2A, which I would imagine would solve the problem - but every time I see mention of it there’s always massive “only do this if you really need to/it might damage things/I did this and my cat turned grey” warnings. Would I regret doing it? Would my cat regret me doing it?


#7

Just an update - max_usb_current=1 does seem to work. Still not sure if it’s a good idea but I’m up and running on a single PSU as hoped.


#8

This week I bought a Retail Picade and having the same problem powering the 8" screen.
I was using a RPi 2B with the official RPi Power Adapter. As soon as I add a WiFi Dongel or keyboard, the power drops and the screen blinks 1 sec. and then turning off.

I’m now using this Power Adapter :

This adapter completed my goal, to have sepperate powerlines for the Pi and the screen, while having just 1 powercord out of my Picade and is working like a charm.

Now 1 powercord comes out my Picade and added a powerswitch to easely cut of the power without having to unplug it and/or opening the Picadedoor.


#9

That’s genius… I’d thought about putting a powered hub inside but I’d never considered putting an actual USB PSU in there, probably because there’s nowhere near enough room in a Picade Mini for anything based on UK 3-pin plugs. But something with an in-line Europlug like that… that’s food for thought!