Video interfaces have gone a long way from the analog TV days to the present era of digital and high-definition television (HDTV). This article will guide you in selecting which video cable you need in interfacing your TV monitor to your signal source.  A number of DIY adapters will also be presented.

Composite Video

This is a type of video connection, which uses a single coaxial cable with RCA-type plugs at both ends.  The video signal is called composite because all the luminance (black and white), chrominance (color) and sync signals are combined into one signal.  This type has the poorest picture quality because of the interference between the luminance, chrominance and sync signals when transmitted in a single cable.

S-Video:

Also called Super Video, this type of video connection was developed to improve the picture quality in composite video.  In this format, chrominance information is separated from a combined luminance and sync information.  Miniature 4-pin mini DIN-type plugs are used at both ends of an S-Video cable.  S-Video is also called Y/C connection: Y for luminance and C for chroma.

Component Video

This type of connection further introduced improvement to the picture quality offered by S-Video.  The luminance and sync information (Y) are combined and run in one cable while the chrominance information is further separated into blue minus luminance (Pb) and red minus luminance (Pr).  These color component signals are run in two more separate cables, bringing the total to three.  The connectors at both ends of the cables are either RCA-type or BNC-type.  Component video is also called YPbPr connection.

VGA

Video Graphics Array is used in connecting a computer to a monitor. A number of TV manufacturers added this input to their sets because of demand from viewers who find it practical to use just one monitor for their computer and their TV viewing. The cable used is multiple-conductor with 15-pin D-sub connectors at both ends.

DVI

Digital Visual Interface is the digital version of VGA.  This is the type of connection that transports uncompressed video signals from the source to the TV monitor.  A DVI cable consists of four pairs of wire - red, green, blue, and clock, and transmits 24 bits of information per pixel.

HDMI:

High Definition Multimedia Interface is a type of digital video connection that also includes up to eight channels of digital audio and consumer electronics control signals. The HDMI digital video signals are electrically compatible with DVI digital video signals. This means sources and display devices with either HDMI or DVI interfaces can be interconnected by using appropriate cable adapters. It should be noted though that the digital audio and control signals will not be transmitted.

Here are a number of DIY adapters you may find useful when you are in situations in which you don’t have the right video cables for the available interfaces.

S-video to Composite Adapter:

This can be used in a situation when your video output device has only S-video output and your TV has only composite video input.  Here is how it works.  Short pins 1 and 2 (Y ground and C ground) of the S-video connector and then connect to composite video ground in the RCA connector.  Also short pin 3 (luminance) of the S-video connector to the hot pin of the RCA connector.  Insert a 470pF capacitor between pin 4 (chrominance) and RCA hot pin. The voltage rating of capacitor can be 10V or more.  The circuit operation is not ideal because impedances are not matched exactly right.  But the picture quality you will get may be good enough for emergency situations.

S-Video pin out            Composite Video connections


1 Y-GND  ---------------------------> Composite GND  

2 C-GND  ---------------------------> Composite GND

3 Y (luminance+sync) ------------> Composite video+

4 C (chrominance)  -------| |-------> Composite video+

470pF    

DVI to HDMI Adapter:

Remember that the HDMI video signal is electrically compatible with the DVI signal.  With this adapter, you can connect directly your PC (with DVI output) on a HDTV monitor with a HDMI input.  Take note that the digital audio and control signals will not be delivered to the monitor.

DVI pin out                 HDMI pin out


1 TMDS Data 2-    ------------------------------> 3

2 TMDS Data 2+  ------------------------------> 1

3 TMDS Data 2 shield  ------------------------> 2 

9 TMDS Data 1-   ------------------------------> 6

10 TMDS Data 1+   -----------------------------> 4

11 TMDS Data 1 shield  ------------------------> 5

14 +5V Power  -----------------------------------> 18

15 GND  ------------------------------------------> 17

16 Hot Plug Detect  -----------------------------> 19

17 TMDS Data 0-   ------------------------------> 9

18 TMDS Data 0+  ------------------------------> 7

19 TMDS Data 0 shield  ------------------------> 8

22 TMDS Clock shield  -------------------------> 11 

23 TMDS Clock+  -------------------------------> 10

24 TMDS Clock-   -------------------------------> 12

DVI to VGA Adapter:

Aside from transporting digital signals, DVI also transport the same analog signals found on a VGA connector.  A simple adapter with connections shown below allows a PC with a DVI output to be connected to a VGA monitor.

HDMI pin out        VGA pin out


C1 Analog red---------------------> 1

C2 Analog green------------------> 2

C3 Analog blue-------------------> 3

C4 Analog Hor sync-------------> 13

C5 Analog ground---------------> 5

8 Analog Ver sync-------------> 14