LCD display panels for Beaglebone Black

[tomizett]

Hi All,
Looking for some advice...

I'm involved in a project which will be using the beaglebone black single board computer. We'll be using this to run a graphical user interface, and will therefore need to connect it to a large-ish (8-15") colour monitor. The board has an HDMI interface, which we may use, but it also has an "LCD interface" available on one of its expansion headers - we'd like the option of using this if possible.

My question is: What is this interface? Is it standard, does it have a name, and where should I look for LCD modules with this electrical interface?
The beaglebone documentation does not refer to the LCD interface in any detail, but judging from the pin names, it appears to have a pixel clock, horizontal and vertical sync, and 8 bits of data per colour (R,G,B). The outputs are all single-ended (not LVDS) 3.3V logic.

I should clarify that I'm not looking for something that plug directly into the beaglebone itself: I'm aware that I'll have to produce an adaptor board, but I would like to find something that is electrically compattible. I'm presuming that the designers would not have brought this interface to a header unless they expected that it would be easily usable.

The documentation for the board is here:
https://github.com/beagleboard/beag...Manual#Figure_50_Expansion_Connector_Location
https://elinux.org/Beagleboard:BeagleBoneBlack

Thanks for reading.

 

[ronsimpson]

I think you will find the HDMI to HDMI interface is low cost.
The "TTL" signals will not work for long distance. The LVDS will work for a long distance.
Years ago when the Beaglebone came out there were many small LCD panels that are TTL. They had a low clock rate and work fine at TTL signals.
I think it will be hard to find a larger LDC with out HDMI input.

 

[tomizett]

So you're saying that the TTL interface has lost popularity due to higher resolutions and refresh rates, which require higher clock rates more suited to LVDS. The panels that I saw which had an LVDS interface seemed to have 4 pairs plus a clock, so they're not simply taking the same signals and balancing them.
I think you're confirming my suspicion that HDMI might be the way to go. Unless anyone else can suggest LCDs that would be suitable?

 

[ronsimpson]

If the computer and LCD are in the same box then you can connect then together with ribbon cable. R0-7+G0-7+B0-7+H+V+I2C+power+many grounds.
My experience is that these cables are built for one use and can not be plugged in and out many times.
When the LCD is not in the same box as the computer you need a simple cable with good connectors.
The HDMI uses shift registers to take 8 or 10 bits of data and send it down a twinax coax wire at 10x faster speed.

 

[tomizett]

Thanks for the explaination and the nice diagram. The connection would be local, in the same box - I'd imagine 10-12 inches or so - so my gut feeling is that we could probably get away with simple TTL. However, that's all accedemic realy if there are no displays available with this interface!

Part of my interest in using the inbuilt LCD interface was because it would be easier to connect to a FFC connector on the "cape" than to arange for a mechanical suport for the micro-HDMI. I also hoped that a more "bare bones" display might be chaper - but no matter.

I think I'll stick to the HDMI. This has the bonus that I don't have to lay out the FFC on the board, or try to solder it by hand.
Appreciate your interest.

 

[Nigel Goodwin]

I also hoped that a more "bare bones" display might be chaper - but no matter.

Probably not, due to it's rarity. How large a display are you talking about?.

 

[tomizett]

Yes, I think you are probably right.
Large enough to use menus and look at some graphs, I reckon probably 10 or 12".

 

[ronsimpson]

For my Raspberry Pi, I am using a HDMI TV. The 1080 TVs look good, but many of the smaller TVs are lower resolution.

 

[Nigel Goodwin]

For my Raspberry Pi, I am using a HDMI TV. The 1080 TVs look good, but many of the smaller TVs are lower resolution.

There are (in the UK at least) two types of flat screen TV's (not counting the later 4K ones). 'Full HD' and 'HD Ready', both have to meet certain minimum specifications to use the logo.

Full HD means 1080 resolution - and HD Ready means it has to meet a certain (lower) resolution - I can't even remember what that is now, but almost all HD Ready sets are actually 768 resolution. For TV it makes VERY little difference, and in side by side tests you often can't tell which is which, and the 768 one may well be better - and certainly a decent make 768 set will be far better than a cheap 1080 set.

For use as a monitor, displaying text, it's a different matter - and 1080 is well worth it, as long as you're wanting to display small text on the screen. If you're wanting to display large text on a screen (such as for a display in a shopping centre) then 768 is just as good.

 

[ronsimpson]

'Full HD' and 'HD Ready

Many people have their Pi or Beagle Bone connected to a cell phone size display. I spend time on the internet with my phone.
I am using a 768 TV because there are free to me and the size is something I can carry around.
The 1080 costs money and is too much in size.
My wife said I need a better job before we get a 4k display.

 

[Nigel Goodwin]

My wife said I need a better job before we get a 4k display.

In my opinion 4K TV's are a waste of time, to be able to see any benefit from the higher resolution you would need to view from MUCH too close (on the tiny amount of 4K programming available) - less than one screen size away. This is why HD Ready TV's (768) are usually just as good as 1080 ones, because it's unusual to view from close enough to be able to see the benefit of 1080 over 768.

For a computer monitor perhaps 4K 'might' be worth while?, at least you're probably close enough to get some benefit from the increased resolution.