AdamC
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Re: VGA over HDMI?

Wed Sep 07, 2011 10:55 pm

Probably a stupid question, but does this particular HDMI interface support VGA with a converter cable. I don't have any monitors/TVs with component or HDMI in, only VGA.

JacksonhC
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Re: VGA over HDMI?

Wed Sep 07, 2011 11:03 pm

you would use the analog out with a VGA converter. not the HDMI

AdamC
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Re: VGA over HDMI?

Wed Sep 07, 2011 11:18 pm

So a $35 converter box then as an additional purchase instead of a 5$ cable? Makes sense to keep the cost down I guess.

JacksonhC
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Re: VGA over HDMI?

Thu Sep 08, 2011 12:05 am

you could get a HDMI to DVI cable but i think it would be hard to get HDMI to VGA as one is digital and the other analog. i could be wrong though.

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Re: VGA over HDMI?

Thu Sep 08, 2011 1:33 am

I used a HDMI to VGA cable from a computer to my LCD TV. It worked OK. I later switched it to DVI to VGA and had a better picture. I understand this does not always work.
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Re: VGA over HDMI?

Thu Sep 08, 2011 7:46 am

Quote from JacksonhC on September 8, 2011, 01:05
you could get a HDMI to DVI cable but i think it would be hard to get HDMI to VGA as one is digital and the other analog.

Several sellers on eBay seem to offer HDMI to VGA cables:

http://www.ebay.co.uk/itm/GOLD.....3efdfba74e

I get the impression, from the description given there, that connecting the Raspberry Pi's HDMI port to the VGA port of a monitor would work, but I'm not sure - although at £2.65 for the cable it's easy enough to just try it and see.

You can get good second-hand 15" LCD monitors in bulk for around £30 plus delivery from places the specialise in recylcing corporate IT equipment, and I actually have a bunch spare at the moment at the school I work at, so it'd be handy if the Rasberry Pi did work with VGA-input monitors.

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Re: VGA over HDMI?

Thu Sep 08, 2011 8:00 am

The cheaper cables won't work - they rely on the computer video card outputing VGA over DVI (DVI_A). The Raspi is purely digital HDMI (compatible with DVI-D). You need something to convert the digital signal to analogue which is more than a simple cable.

Component to VGA, I am less sure about.

There are threads in the forum about this.
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mgb
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Re: VGA over HDMI?

Thu Sep 08, 2011 6:01 pm

The HDMI-VGA cables are for systems that have a VGA output and simply share pins on the HDMI connector to save space. This would require extra chips and power on a raspberry.

You can get a standalone HDMI->VGA boxes (essentially a graphics card in a box) for about $30 (eg http://www.dealextreme.com/p/h.....rter-71816)

vladhed
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Re: VGA over HDMI?

Thu Sep 08, 2011 6:13 pm

Component to VGA can be a simple cable - provided the VGA monitor can grok the frame timing that the source can generate: 480i, 480p, 576i, 576p, 720p, or 1080i. For example my old VGA monitor has no trouble displaying my Wii (480p) because the signals and timing are identical to 640x480.

This is moot, however, since the R-Pi doesn't generate component signals.

Composite to VGA can be done with analog only circuitry, provided the VGA monitor is very forgiving and can handle interlaced signal. All boxes I have seen have scan converters so as to output standard 640x480 VGA (NTSC) or 800x600 SVGA (PAL). I have seen these for as little as 32$US (see monoprice.com) - though they also have a HDMI (DVI-D) to VGA for only 8$ more.

AdamC
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Re: VGA over HDMI?

Thu Sep 08, 2011 7:49 pm

The cost isn't as much of a problem as the size of an additional box plus power, but thanks for the monoprice suggestion. Maybe I can shrink one of their boxes with judicious reworking and it's 5VDC 2A so I could use a shared power supply.

starhawk
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Re: VGA over HDMI?

Wed Sep 14, 2011 4:53 am

I'm willing to bet that I can do this for less than US$10. There's more than one way to send a cat to Saturn ;) The trick I came up with uses two adapters that are VERY inexpensive.

HDMI, electrically, can be made to use the same protocol as DVI-D. I don't know if that's its native protocol, but that's one of the options -- in other words, it can emulate (non-technical: act the same as without actually being) DVI-D. An HDMI->DVI-D adapter costs me about US$5-7 (depending on where I get it and how generous I feel like being to Corporate America). But, I hear you say, that doesn't get me analog VGA. Strictly speaking, you're right. DVI-D is the purely digital part of it. Now go out and get yourself another adapter. Specifically, one for DVI-D->VGA. Cost? US$2-5 (again, depending on source and wallet-generosity).

Of course, you need to be careful with your adapter selection, because a plain DVI->VGA or a DVI-A->VGA adapter will waste your money by looking for a set of four pins (the ones put with that cross-shaped thing) that the HDMI->DVI-D converter, by nature cannot give you. So they won't work, and chances are, won't even fit.

You know why I thought of this? Simply put: I'm poor. I'm used to "duct tape solutions" that just barely work well enough to get the job done. Being unemployed, I've got plenty of time to futz with it if it decides to stop working tomorrow. "Jerry-rigging" is a very useful skill in this day and age ;) and I'm dern good at it when I need to be. I'm not the smartest cookie in the bag, and I know it well -- but I also know that, no matter how I might feel at any given time, I'm not the dumbest, either.

henkschuifkaas
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Re: VGA over HDMI?

Wed Sep 14, 2011 7:42 am

Quote from starhawk on September 14, 2011, 05:53
DVI-D is the purely digital part of it. Now go out and get yourself another adapter. Specifically, one for DVI-D->VGA. Cost? US$2-5


I think *that* is the problem, you're gonna need some digital (DVI-D) to analogue (VGA) conversion. Not just an adapter. These cheap adapters are analogue (DVI-A) to analogue (VGA).

starhawk
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Re: VGA over HDMI?

Wed Sep 14, 2011 8:02 am

That's funny, they certainly advertise DVI-D -> VGA adapters ;) check google shopping -- the images do show the correct pinout (i.e. a - and no pins instead of a + surrounded by four pins) for a DVI-D connector on one end, and it sure as heck looks like a VGA port on the other end (I don't think DVI->COM exists, either).

That said, if all that's needed is a DAC (digital->analog, not a specific fancy protocol), there's more than one way to do that, too ;)

Michael
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Re: VGA over HDMI?

Wed Sep 14, 2011 8:11 am

This has been covered on the forum several times before and is also covered in the wiki:
http://elinux.org/RaspberryPiB.....GA_Adaptor

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