PatrickJ
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Joined: Tue Apr 17, 2012 10:18 am

Re: Getting the full picture with your Pi or at least something on the screen...

Tue Apr 17, 2012 12:05 pm

Having just got my Raspberry Pi operational I thought I'd cover some video related issues and how you might sort them out too.

Firstly, I plugged everything into my Pi and didn't get a picture (even with SD card done, lights on etc).

So, I opened up a DOS box on my PC and pinged the new IP address that my router showed, so I knew it was 'on' and the SD card's OS image was operational.

Then, I realised that the HD TV and HDMI cable I were using had never been used/proven to work.  By swapping inputs/TVs/cables I fault-found the right TV with the right input using the original cable.  I could have used a DVD player as a way to prove the connection, but I didn't need to in the end.

Right, now I had a picture on the screen (or rather a scrolling cascade of white text on a black background as the Linux OS displayed its boot-up sequence diagnostic information).  However, due to my TV trying to show things in widescreen the screen was clipped on each of the edges.  This is common on a lot of TVs, where losing some of the picture at the extremes of the edges is part of how their formats are altered.  Unfortunately, this means you might not be able to read all the words/see the whole screen.

In my case, I couldn't see the bottom line, so although I suspected that there was a login prompt just out of sight I wasn't sure.  Hitting return a few times at this point caused no harm and confirmed this.  So (as I was using Debian) I just typed in pi <return> then raspberry <return> to login.  Hitting <return> a few times again proved that my login was successful.

To then get the graphical interface going just use startx <return>.

This should get the GUI visible and it might be that your TV correctly synchronises to the video it is getting and your problems are solved.  Turning the TV off and on can also sometimes get it to make a better guess at things and improve the display.

In my case, I still had the 4 edges of the screen missing.  To get things started I moved the mouse cursor off the bottom left screen corner and left/right clicked until I hit the panel controls dialog.  This meant that I could enlarge the panel bar to be larger and therefore visible so that I could proceed.  You can also move it to the top or one of the sides if this helps.

Ultimately, I found the full answer to be in my TVs more obscure settings.  For me, on my LG TV, changing the aspect settings from 16:9 to 'just scan' gave me the full picture.  In this case, this made my TV change its screen view to match the incoming video from the Pi instead of trying to preserve the 16:9 ratio favoured by Sky boxes etc.

I hope that helps.

aeiah
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Re: Getting the full picture with your Pi or at least something on the screen...

Tue Apr 17, 2012 1:03 pm

ignore my ramblings, overscan settings can be set in config.txt

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frying_fish
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Re: Getting the full picture with your Pi or at least something on the screen...

Tue Apr 17, 2012 1:36 pm

As found though, it isn't overscan settings on the RPi that need to be set, but the correct mode on the TV itself. A lot of HDMI input are still set to be 16:9 instead of "Just Scan" so it artificially scales the output, even though it should be the correct number of pixels.

We now know that both Samsung and LG display the correct option in their tools menus as "Just Scan". Can anyone else comment on other brands of television and what they call this mode? - You don't need a pi to check this, just open up the tools menu on any TV HDMI input and see what picture options it gives.  I found this all a pain a couple of years back when putting together my HTPC.

bob franklin
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Joined: Thu Jan 12, 2012 8:21 pm

Re: Getting the full picture with your Pi or at least something on the screen...

Tue Apr 17, 2012 2:01 pm

Yes on my tv Luxor the settings were menu/picture/advanced settings/picture zoom set it to full it was then perfect now just struggling with wifi have three different dongles and non seem to request firmware oh well will carry on this reply was sent via the pi via ethernet

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Bollard
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Re: Getting the full picture with your Pi or at least something on the screen...

Tue Apr 17, 2012 9:27 pm

My TV is an Orion (was dirt cheap way back for a 720p 32inch) and has no overscan options…

How can I edit this config.txt? I tried adding one to the /root directory when I had logged in to Debian but it failed. Said I didn't have permission.

Also, I think my keyboard (Logitech G15) doesn't work at all. It lights up, but I was unable to log in at the boot screen. I had to go grab the bog standard Dell from downstairs.

EDIT: Turns out its easiest to make the config.txt in Windows, and paste it on to the ~75MB partition Windows can still access on the card. Works like a charm now.

Plus I got my keyboard working by turning off the backlight (for some reason). On half it would repeat the keys I entered and on full it did nowt, off it works great.

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abishur
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Re: Getting the full picture with your Pi or at least something on the screen...

Tue Apr 17, 2012 9:50 pm

Looking at a pic of that keyboard, my guess is it uses more than the 140 mA maximum output of the USB ports
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Bollard
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Re: Getting the full picture with your Pi or at least something on the screen...

Tue Apr 17, 2012 9:52 pm

Abishur said:


Looking at a pic of that keyboard, my guess is it uses more than the 140 mA maximum output of the USB ports


Maybe that's why turning the backlight off helped! And I didn't know about that specification thanks. Do you know if that amount is affected by the current in? Like, they suggests a 500mA minimum, 700 mA is recommended and I'm using a 1 A power adapter at the moment. I wonder if that would have any effect.

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abishur
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Re: Getting the full picture with your Pi or at least something on the screen...

Tue Apr 17, 2012 10:10 pm

That 500mA that was suggested in the documentation that came with the pi?  I have no idea where that came from.  All I've ever heard from the RPF was 700mA minimum for the Model B.

Adding a higher current PSU would only help up to a point.  The USB ports each have a fuse that trips whenever more than 140 mA are applied to its respective port.  So no matter how many Amps your PSU could supply, the usb ports would never provide more than 140 mA... well never unless you desolder the fuses and replaced them with a higher rated fuse.
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Simon H
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Re: Getting the full picture with your Pi or at least something on the screen...

Wed Apr 18, 2012 11:40 am

I had the same keyboard problem when I plugged a wifi dongle in the USB, kept repeating and the Wifi couldn't see any access points even though it saw the dongle and loaded the drivers .

Moving the dongle to a powered hub solved all the problems and I also power the Pi from the hub using a USB to Mini/Micro USB lead instead of a power supply, just needs 1 wall wart then.

The 5v suppy I have powering the Hub is rated 4A which is way over the top but was what I had lying around and gives plenty of margin for anything else I plug into the hub like HDD.

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Tass
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Re: Getting the full picture with your Pi or at least something on the screen...

Wed Apr 18, 2012 11:50 am

Abishur said:


That 500mA that was suggested in the documentation that came with the pi?  I have no idea where that came from.  All I've ever heard from the RPF was 700mA minimum for the Model B.


Yes, for some reason the paperwork that Farnell included states a maximum of 500mA

nimdy
Posts: 67
Joined: Sun Mar 04, 2012 2:54 pm

Re: Getting the full picture with your Pi or at least something on the screen...

Wed Apr 18, 2012 8:47 pm

I had some issues with my display earlier. The device would boot, but the TV just said 'no signal'.

I've added these lines to the config.txt:

hdmi_force_hotplug=1

hdmi_mode=16

but now I find that the picture is in the middle with a thick border round each side. My display is an LG M228WD LCD TV connected to the HDMI. Its one of these odd 16:10 tvs, which I think is why it is causing me bother with the Pi. Can anyone help?

tkp
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Joined: Thu Apr 12, 2012 6:32 pm

Re: Getting the full picture with your Pi or at least something on the screen...

Wed Apr 18, 2012 9:03 pm

On the power side: there are 2 docs from RS - 1 says 500mA max, while the other says 700mA.

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Gert van Loo
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Re: Getting the full picture with your Pi or at least something on the screen...

Wed Apr 18, 2012 9:24 pm

It should say 700mA minimum. The 500mA is an error.

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