Amiga RGB to Component video output

[kipper2k]

Hi All,

I been checking out new TV's and pretty well S-Video seems to be a thing of the past now as all the new ones no longer have S-Video inputs. I have been reading old threads and looking at the possibility of RGB conversion to component video (Red, Green and Blue outputs)

Something that has me interested is the LT6550/1 IC. here is the datasheet.

www.kipper2k.com/amiga/lt65501.pdf

and here is a sample schematic that is shown on the datasheet.


I look at this schematic and and from what i see is that i use 2 of these IC's and feed my RGB outputs from the Amiga into the left LT6550/1 and then simply use the Pr, Y, and Pb outputs on the right sided LT6550/1 to the component input on the TV.

Is it this simple or am i missing something ?.

Any help would be greatly appreciated

thanks

[meega]

Where is the (composite) X/Y scan signal coming from?

Ed: A500 MONO video out is essentially (Gx0.6) + (Rx0.3) + (Bx0.1) + (X/Y scan) = Y (brightness) + scan, job done.

Ed2: I think... it makes sense as without the scan you are relying entirely on the receiving device's flywheel to control aspect ratio, which might not always work. Tell it how fast to go across and down in the same signal as you tell it how bright to be and you get a proper picture.

[Stedy]

Hi,

There is no sync information on the Amiga's RGB outputs.
You will either need to take the TTL CSYNC signal and add it to the Y output or take the composite video signal and process that.

The HSYNC, VSYNC or CSYNC signals from the Amiga are HCMOS, logic 1 >4.5V and logic 0 <0.2V.

Take a look at this design from Narmi, http://eab.abime.net/showpost.php?p=635282&postcount=13

The LT65501 looks like a good choice.

Ian

[kipper2k]

Originally Posted by Stedy

Hi,

There is no sync information on the Amiga's RGB outputs.
You will either need to take the TTL CSYNC signal and add it to the Y output or take the composite video signal and process that.

The HSYNC, VSYNC or CSYNC signals from the Amiga are HCMOS, logic 1 >4.5V and logic 0 <0.2V.

Take a look at this design from Narmi, http://eab.abime.net/showpost.php?p=635282&postcount=13

The LT65501 looks like a good choice.

Ian

Thanks for the headstart Ian, I have ordered the parts and hope to have something in a few weeks

[kipper2k]

Heres a start on the circuit that hopefully will give composite, svideo and component output from the Amigas. The main circuit that controls the svideo and composite outputs is 1.3" x 1.45" (that portion of the board is complete). I have made edge connector pads top and bottom so that the board can slide between a 23 pin connector and then be soldered right to the pads .



The bottom part of the board is just the traces for the LT6551. The legs are 0.020" apart with only a 0.010" gap between so hopefully i can get the board fabricated by Futurelec. One thing i noticed about the LT6551 as well is you can take a Luma and Chroma output from any source and feed it back into this chip to amplify it. I am going to see if this can produce a nicer Svideo with more brighter colours. If anyone wants a look at the Expresspcb file let me know

[gulliver]

Really cool. If at some point you attempt to sell fully mounted boards, I am really interested.

[kipper2k]

Originally Posted by gulliver

Really cool. If at some point you attempt to sell fully mounted boards, I am really interested.

I will probably try to get it mounted into a plastic case that plugs right into the Amiga rgb connector.

[gulliver]

Even better!

[Kakaboy]

Originally Posted by kipper2k

I will probably try to get it mounted into a plastic case that plugs right into the Amiga rgb connector.

I'm in too Kipper

[kipper2k]

I traced out the circuit, I was able to get the circuit size down to about 1.2" square. The circuit is the same as on Page 14 of the datasheet so its not that hard. I have added the RGB and Sync input points to the board so its just a case now of combining both circuits to port over the required inputs to the RGB portion.
I'll recheck the board tonite and mabbe add a couple more things to the board (Futurlec charge a setup fee so i try to cheap out and add a few small circuits to each board i order so i don't have to pay a setup fee for each board design)



ps i just found one small error on this... Seems the more you check it the more you cant see the errors. i just noticed this after taking a break

[Kakaboy]

@Kipper2k

How does component compare to S-Video in regards to picture quality ?

[kipper2k]

Originally Posted by Kakaboy

@Kipper2k

How does component compare to S-Video in regards to picture quality ?

heres a better answer than i could give...

http://www.lyberty.com/encyc/articles/svideo.html

for most people, you would not notice the difference between HDMI and component video. If you have a xbox 360 and you have both hdmi and component outputs on it, try each output and you will see (or maybe not) very very little difference in colour and sharpness. Composite as we know causes dot crawl and fuzziness, Component is a really nice option, and hopefully this circuit will work good. Total cost of the board and components i reckon is about $45 - $50. and it will contain composite, S-Video, and component.

[kipper2k]

I'm having a hard time trying to find a way to get -3.3v power input to this IC. The Amiga 23 pin RGB output A500, A600 and A1200) only has -12v, +12v and +5v. I haven't had any luck trying to find a -3.3v Voltage regulator or finding a simple way to drop the Amiga -12v output to -3.3v with an efficient circuit that doesnt draw too much current. Anyone any ideas ?

thanks

[gulliver]

Have you tried with:

PT5021 from Texas Instruments

It will convert +5v to -3.3

or

PT664 from Texas Instruments

It will conver +12 to -3.3

[kipper2k]

Originally Posted by gulliver

Have you tried with:

PT5021 from Texas Instruments

It will convert +5v to -3.3

or

PT664 from Texas Instruments

It will conver +12 to -3.3

ouch, $18.00 each, and thankfully non stock items, Theres a pile of +ve voltage regulators out there, but very few -ve ones.
Digikey and newark.com are the places i normally get my parts from and i've had no luck so far

[meega]

Originally Posted by kipper2k

... or finding a simple way to drop the Amiga -12v output to -3.3v with an efficient circuit that doesnt draw too much current. Anyone any ideas ?

thanks

How many mA do you need? Two resistors make a voltage divider.

[kipper2k]

Originally Posted by meega

How many mA do you need? Two resistors make a voltage divider.

Thanks for your input

100 ma should be sufficient. I was thinking of a voltage divider using the -12v line and a 3.63:1 ratio on the resistors. I'm not sure what the heat generation would be like. i guess only way to find out is to get a couple 1/4W resistors and give it a try

[Anemos]

i found this maybe is helpful ..> http://www.bowdenshobbycircuits.info/r2.htm

[meega]

Originally Posted by Anemos

i found this maybe is helpful ..> http://www.bowdenshobbycircuits.info/r2.htm

Bookmarked.

[kipper2k]

Originally Posted by Anemos

i found this maybe is helpful ..> http://www.bowdenshobbycircuits.info/r2.htm

Thanks Anemos,

Thats a nice little tool. The IC typical current is 10 - 15ma so using that tool it says at 12v input, and 3.3v output with a typical current of 10ma, the divider should be 870 ohms/330 ohms. I'll play around later and see if theory holds true

thanks