The HDMI Mojo



nearly as good was cheaper to purchase and maintain. The influence of the pornographic film industry on the three formats, which included the Phillips 2000 was also noticeably focused on the VHS market. As the technology evolved through the 70s and 80s quality improved but unfortunately by the 90s the writing was on the wall, the optical disk format was obvious first choice. Like the VHS and Beta debacle, we were suddenly thrown into the deep end: DVD-R or DVD+R? HD or Bluray? VGA to SVGA to 16:9 aspect ratios, plasma or LCD now to LED. If one thinks this is confusing, think now of the myriads of cable types now flooding the market. I can purchase a HDMI cable but my plasma is DVI. I need a converter. I now have a second TV which is the older 4:3 aspect CRT television receiver plus a Samsung 23”LCD which has an HDMI input. Throw in a Phillips LCD 4:3 with a standard D-sub 15 pin connector. Never before has one seen such a wide range of different receptacles been used in a household where each technology is different but all (mostly) current. CRT monitors and television receivers are a thing of the past but can still be picked up at the corner store. I know of at least three graphics design and CAD power users that stick with 21” CRT monitors, not because they are cash strapped but because they prefer the colour ambience of these monitors over LCD. Also CRT monitors can change their native resolution through switching circuits – LCDs cannot. They have a native resolution and any resolution outide this resolution makes text difficult to read. Confused? So am I. Here’s some gen on connectors used in the audio video industry.

Electrical connector:- Wiki: “An electrical connector is a conductive device for joining electrical circuits together”.

RCA Connector:

rca

 An RCA connector is used in both audio and video, good quality connectors are often gold plated to reduce resistance losses. The outer connector is often the shielded part which is grounded. The centre electrode transfers signal.

The D-Sub 15 pin connector

 dsubconn

 

Display Data Channel or DDC comes in two distinct varieties: DDC 1 which allows for one direction only, from the monitor to the graphics card – monitor recognition. DDC2 is bi-directional and has a data clock. DDC1 and DDC issues are rare – open circuit lines are often the cause of the monitor not functioning to full capability or non display of monitor type. My own experience is that pins 1, 2 or 3 are often the most prone to user damage. Pins 1, 2, 3, 13 and 14 going open circuit because of customers pulling on the cable and not the connector are the most visible on display. How many times have technically minded people scratched around in the H-Sync circuitry only to find a bent pin or open circuit cable – this includes myself.

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The DVI Connector

 dviconn

And now for the latest, at least from 2002: HDMI (High Definition Multimedia Interface).

 

hdmiconn

HDMI switches and splitters.

After extensive reading up on this matter there seems to be an element of confusion . a) switches are like the old KVM, Keyboard, Video and Mouse – likewise the switch can take more than one source and apply it to the display or displays b) splitters are the opposite – they take one input (or more) and apply it to more than one display (or only one). There are some hurdles to overcome. The perfect switch will not have any contact resistance so circuits should theoretically be electronically bypassed. By this I mean that a DIYer should not use mechanical switches – rather use a configuration of electronic gates. The perfect splitter must look at what all is required to drive more than one display e.g. does one require the CEC (consumer electronics display), the DDC (display data channel) – in most cases this may be very important. Can one use a standard cable in a Y-configuration, which at basic level means that the cable outputs are just bridges to two or more separate output? Unfortunately, although an inexpensive solution it is not advisable – the reason why we want HDMI is because of the bandwidth factor – we want the hi-definition. Outputs can be switched between more than one display which essentially should not hinder performance but running all displays off the same input is bound to impact the quality – it would be a recommendation to build in a buffer of sorts which does not load the source output. Are there schematics available? Well, to test the theory that the web is full of advertisements that is exactly what we found. There are some entry level designs from about 34U$D to some pretty expensive solutions, popular unit costing 1400U$D but very little of value with regards to schematics. Note: You will get what you pay for my friend. I’m all for having one good quality splitter and not one that has to be controlled/switched on through your PC. For technically minded people wanting to learn more and experiment, a PC based home entertainment centre is the obvious choice but not for the person on the street wanting to come home, switch on his digital satellite decoder and have the outputs piped through to all the household/office television receivers/monitors.

To kick off with you may need to do a little bit of research first of all on HDTV – Texas Instruments has laid out a fairly good description here. Video Design Line has some pretty hot information as well. Go here.

Well after some pretty much fruitless searches I can honestly say that there’s a lot more information on switches than splitters – is this because of the Intel HDCP? – Digital Copyright Protection. Giving the DIYer an inside look at the schematics might make the enquiring mind kick into overdrive – but that HDCP seems to be a spanner in the works. Forums are full of posts from users wanting an inexpensive solution to splitting their signals – a very common complaint is that in most cases the split signal will only communicate with the first device and not the second. And then some complaints about lack of audio. Abig problem may be the very fact that the source needs to communicate with the load. 

I don’t think so…

Wiki: “HDCP does not address whether copying would be permitted by ‘fair use’ laws. The specification is proprietary, and implementing HDCP requires a license”. Ad nauseam, etc, etc.

I am going to do some research this month and get some real answers. In the meantime, readers of this article are welcome to drop us a line. The ideal respondents should be manufacturer programmers of course.

 

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