Schema Converter VGA / TV / RCA

 

 

The printed circuit:

Here is the PCB for connecting the VGA to SCART (SCART). It is mainly a scheme that takes the VGA signal and converts the signal to RGB + composite sync, which are injected to the TV via the SCART or SCART. On maps VGA signals RED, GREEN and BLUE are already at the right voltage level (0.7Vpp) and good impedance (75 ohm) for direct connection to the corresponding inputs on the TV.
What we must do is mix the Horizontal Sync Vertical Sync with the VGA card to get the signal of Composite Sync is necessary for the video input (pin 20) of the TV SCART . This sync signal conversion is made by the electronic scheme. Is positioned as a signal to the pin (16) of the order RGB on SCART (SCART).

Principle:

The circuit is very simple, because the output signals V R B of the VGA card is already standard 0.7Vpp and 75 Ohms.
For the synchronization signals, there is a circuit which mixes the signals Horizontal and Vertical Sync to get the signal from the composite sync. The circuit is simply based on one TTL chip with four XOR gates (exclusive OR), two resistors and two capacitors. The chip is TTL logical choice because of TTL levels VGA sync signals.
The sync signal mixer has a system that adjusts to the different polarities of sync signals so that the composite sync is always correct. VGA cards use different polarities and timing of the sync signal according to the different resolutions exhibited by the monitor. This circuit adjusts to changes in polarity of the sync signal in less than 200 milliseconds, which is faster than the time it takes a conventional VGA monitor when changing the display mode.
The circuit needs a well regulated power supply +5 V (+ / -5%), consuming about 120 mA. It also needs a specific driver ( More info: site in English ).

Construction of the circuit:

VGA Converter => TV is quite easy to build if you have some experience in building electronic circuits. Circuit components can be easily mounted on a small card type veroboard study.
Attention must be added the supply lines to the chip U1. They were not marked on the diagram. U1 to ground at terminal 7 and 5 V to terminal 14.
The circuit needs a well-stabilized power supply with a voltage of 5 V (the actual voltage can vary between 4.75V and 5.25V). The circuit consumes less than 150 mA current, so you do not need a big power. If you have nothing suitable, you can always use a small transformer and a small all-purpose control circuit voltage 5 V. If your graphics card complies with VESA DDC, it can have the +5 V available at terminal 9 of the VGA connector (the standard says that pin 9 can have the +5 V is an option but not required) . You can easily test the presence of +5 V using a multimeter.
The image below (copper tracks displayed side components):

The image of the map here is a scanned version (scanned at 300x300 resolution) of the actual map in GIF format (the image size is 1227x672 pixels). You must use an appropriate program to print in the correct resolution so as to obtain an image with the size 4.09x2.24 inch (your browser (browser) is useless here).
The card is designed to accommodate the electronics around the chip 74LS86 adding the small power supply regulated +5 V required. The image below shows what it looks like this circuit.

The VGA connector, SCART connector and other connectors must be tailored out of this card. Remember that the circuit is provided to connect the pins of the SCART, the latter being connected directly to the TV. We will use a cable with a male SCART connector directly connected to the TV.
If you put a female connector plugs into a scart cable trade will require that the pins of the cable are all connected.
For a quality signal all wiring must be done in 75-ohm coaxial cable (thin wire antenna) for a better quality image as in any circuit video.
The TV did not display very high resolution, the type of wire is irrelevant as the cable does not exceed several meters in length. We can use a computer video cable with two twisted pairs for connections (one pair for signal and one for ground). Use the cable well protected because of poorly protected video cable can produce radio interference.

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Possible options:

Adding the ID signal monitor:

If you plan to use TV as a single monitor, you could add the function of identifying the monitor circuit.
This can be easily done by connecting a wire terminals 11 and 5 of the VGA connector. In this way the graphics card gets the identification "ID" of the monitor and you can boot your computer in monitor mode when the converter VGA / TV is connected.

Problem screen mode on 16:9 TV:

The +5 V sends the circuit to pin 8 (AV control) of the SCART (SCART) is sufficient to switch the TV to video mode. Unfortunately on some TV (mostly recent), there may be problems, this tension is set to switch to 16:9. If you experience these problems, replace the voltage (pin 8) with a 9.5-12V voltage of another power.

Added sound on the HP TV:

Another nice change is to add the computer's sound to the speakers of the TV. Simply connect the right audio out sound card to pin 2 of the Scart, the left output to pin 6 of the SCART and the mass of the sound card to pin 4 of the SCART.
It is advisable to use shielded cable for the sound to avoid noise due to the video of the TV.

Warnings:

If you try this circuit with these drivers so consider what you are doing and check the circuit more ways than one. A single mistake can damage your TV or your video card. Remember that you try all this at your own risk and I accept responsibility on some damage whatsoever. Attention it is always possible that the circuit can not work on your system due to different characteristics of video cards and TVs.

List of components:

U1 74LS86 (74HC86 or 74HCT86)
C1 Electrolytic Capacitor 22 microfarad 16V
C2 47 uF 16V Electrolytic (possible problem with the 22 uF noted on the diagram)
R1, R2, R3, R4, R5 2.2 kOhm, 1 / 4 W
R6, R7, R9 47 Ohm, 1 / 2 W
R8 120 Ohm, 1 / 2 W
T1, T2 BC547B (2N2222 attention but different pinout)
Connectors:
SUB-D HD15 pin
SCART 21-pin

Wiring:

Video signals Red, Green, Blue and Composite Sync must be wired in 75 Ohms coaxial cable for improved picture quality, but you can use the normal cable without screen.

Components of the diet:

Cruise 7805
100 uF 25V Electrolytic
10 uF 16V Electrolytic
Capacitor 100 nF ceramic or polyester
AC / DC 8-18V with output and 150 mA.

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