RGB to composite - subcarrier for cxa1645 ??

B

Budd

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Hi,

I started a little project, to insert a neo geo MVS 1-Slot in my car.
I allready got a little 7" monitor, but it only works in NTSC mode and has only got a composite IN. So I need to convert the RGB signal somehow. I got the cxa1645 for that, everything seems to be clear in connecting it - I only have problems to understand, what to connect to pin 6?

the data sheet says following:
PIN 6 SCIN —
Subcarrier input.
Input 0.4 to 0.5Vp-p sine wave or pulse.
Refer to Notes on Operation, Nos. 3 and 5.

3. The SC input (Pin 6) can be either a sine wave or a pulse in the range from 0.4 to 5.0Vp-p.
However, when a pulse is input, its phase may be shifted several degrees from that of the sine wave input.
In the IC, the SC input is biased to 1/2 VCC. Accordingly, when a 5.0Vp-p pulse is input and the duty factor
deviates from 50%, High- and Low-level pulse voltages may exceed VCC and GND in the IC, which causes
subcarrier distortion. In such a case, be very careful that the duty factor keeps to 50%.

5. SC and SYNC input pulses
Attach a resistor and a capacitor to eliminate high-frequency components of SC (Figure A) and SYNC
(Figure B) before input.



ok, that's what they tell me, but I dont really understand, what that means. is it some kind of quartz crystal - or do I just have to connect 0.5 or 5.0 Volt in there?

I hope, somebody may help me.
 
B

Budd

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yes, I thought about this gaming by driving, but I think I'll better let someone else do that driving job, while I care about Garou :-)
 
mainman

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Budd said:
Hi,

I started a little project, to insert a neo geo MVS 1-Slot in my car.
I allready got a little 7" monitor, but it only works in NTSC mode and has only got a composite IN. So I need to convert the RGB signal somehow. I got the cxa1645 for that, everything seems to be clear in connecting it - I only have problems to understand, what to connect to pin 6?

the data sheet says following:
PIN 6 SCIN —
Subcarrier input.
Input 0.4 to 0.5Vp-p sine wave or pulse.
Refer to Notes on Operation, Nos. 3 and 5.

3. The SC input (Pin 6) can be either a sine wave or a pulse in the range from 0.4 to 5.0Vp-p.
However, when a pulse is input, its phase may be shifted several degrees from that of the sine wave input.
In the IC, the SC input is biased to 1/2 VCC. Accordingly, when a 5.0Vp-p pulse is input and the duty factor
deviates from 50%, High- and Low-level pulse voltages may exceed VCC and GND in the IC, which causes
subcarrier distortion. In such a case, be very careful that the duty factor keeps to 50%.

5. SC and SYNC input pulses
Attach a resistor and a capacitor to eliminate high-frequency components of SC (Figure A) and SYNC
(Figure B) before input.



ok, that's what they tell me, but I dont really understand, what that means. is it some kind of quartz crystal - or do I just have to connect 0.5 or 5.0 Volt in there?

I hope, somebody may help me.
Click to expand...

What they mean by duty cycle is the ratio of a pulsating circuit high time to its low time expressed in this formula (TH / (TH + TL) * 100

They want you to keep the duty cycle to 50%

Let say you have a square wave with a total cycle of 10 milli seconds. For 5 milli seconds the wave is high and for 5 milli seconds it was low that means its duty cycle would be ( 5/ (5 + 5) X 100 = 50 %

You could do this two ways

Use a 555 timer confiqured as a Astable circuit outputing exactly what you need requiring little math or know how but more parts

Alternately you can use a resistor and capacitor like the data sheet said in a RC time constant circuit. This way require only two part but require a little more math and the knowledge

And on the SYNC input you will have to use a cap to eliminate and filter any noise
 
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B

Budd

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thanks for your explantion,

I think I will go the way with the 555 timer,

so I will have to create an astable circut, with a 555, two resistors (R1 and R2) and a capacitor.
so the only thing I have to care about is, that HIGH time / pulse period time = 1/2
did I understand that right?

will I not have to care about the frequency outcome ( 1,44 / (R1 + 2*R2) * Cap )?
 
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B

Budd

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it's not ready, yet - but I will post some, when I get it working...
 
mainman

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Budd said:
thanks for your explantion,

I think I will go the way with the 555 timer,

so I will have to create an astable circut, with a 555, two resistors (R1 and R2) and a capacitor.
so the only thing I have to care about is, that HIGH time / pulse period time = 1/2
did I understand that right?

will I not have to care about the frequency outcome ( 1,44 / (R1 + 2*R2) * Cap )?
Click to expand...


Yes if I understood you right the only thing you have to worry about is the high time is = to half of the total pulse ( duty cycle )

About the frequency, spend most of your attention trying to get the duty cycle to 50 % first and worry about the frequency last because the 555 timer will only let you have it one way. It will only let you have a real high duty cycle or a real high frequency. I believe as you increase the resistance of the potentiometer R1 the time the wave is high will decrease

Time high = .693(r1+r2)C
Time Low = .693 X r2 X C

So technically R1 will have to be (ALMOST) equal to R2

Frequency = 1/(.693 X C X (R1 + 2 X R2 )


Do you have a Oscilloscope, it would really help in this situation because in your case you need to see the square wave.

In my use of the 555 timer I only use it as a timer, so I only cared about the frequency and not the duty cycle so I never needed to check the wave with a Oscilloscope.
 
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ttooddddyy

ttooddddyy

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Im not sure the resistance will be that critical for the application, a tweak of the pot should fix it.

This is the tech forum, but do we need to get so teck- said jokingly :kekeke:
 
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mainman

mainman

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ttooddddyy said:
Im not sure the resistance will be that critical for the application, a tweak of the pot should fix it.

This is the tech forum, but do we need to get so teck- said jokingly :kekeke:
Click to expand...

Huh, the resistance ( resistors ) are the heart of this timer it is important.

I am not getting to teck not once did I use the words flux capacitor or Dilithium Crystal
 
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Reznor007

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Just hook up a 3.579545MHz crystal. That's the NTSC color subcarrier frequency that it needs.
 
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Budd

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Reznor007 said:
Just hook up a 3.579545MHz crystal. That's the NTSC color subcarrier frequency that it needs.
Click to expand...

I thought about using a crystal, but how do I have to connect it to pin 6 of the cxa? I'm really not familiar with that...

if I use the 555 timer, wouldn't I have to set the frequenz near the 3,579...?
I think keeping the duty cicle near 50 % is quite simple, I take a small R1 and a big R2

thanks for your help
 
mainman

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Budd said:
I thought about using a crystal, but how do I have to connect it to pin 6 of the cxa? I'm really not familiar with that...

if I use the 555 timer, wouldn't I have to set the frequenz near the 3,579...?
I think keeping the duty cicle near 50 % is quite simple, I take a small R1 and a big R2

thanks for your help
Click to expand...

Still haven't gotten it working uh, how far have you gotten? Ok your going to need alot of high end equipment like a Oscilloscope to see the wave form and a frequency counter to determine the frequency. Without this equipment if you do not have the patience for trail and error your not going to succeed at anything at least using the 555 timer. I mean without any test equipment how will you be able to really determine any of your needed values. And yeah I forgot you do need to keep the frequency near 3,579 hz.I suggest you try using the crystal like the other guy suggested because I only recommended the timer to you assuming you worked with it before, maybe the crystal would be a better solution. To be honest if it was such a simple task for anyone to build a rgb converter everyone would be destroying sega genesis to make their own and jrok wouldn't have any customers. The one I build used a different chip and came with a sheet containing a total list of all the component I would need. Unfortunately I do not believe this chip is still manufactered.
 
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B

Budd

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I think I could get it working with a crystal - somehow building it after Mega Drive or AES - but they use the old cxa1145 there, and I didn't find a good data sheet, only some japanese stuff. and it will be really hard to follow all wires that are needed.

but there must be another solution, like using some Crystal Oscillator, like Epson produces them. perhaps somebody may know which one I could use...

yes, or I buy a jrok, but that's expensive and doesnt make fun,
and I have nearly all the parts I need
 
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R

Reznor007

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Budd said:
I thought about using a crystal, but how do I have to connect it to pin 6 of the cxa? I'm really not familiar with that...

if I use the 555 timer, wouldn't I have to set the frequenz near the 3,579...?
I think keeping the duty cicle near 50 % is quite simple, I take a small R1 and a big R2

thanks for your help
Click to expand...

Connect the output pin of the 3.579545MHz crystal to pin 6 with a wire or something. That's all you have to do really. I've built a RGB to NTSC converter myself, but it was using an AD725 instead of the Sony chip. Same basic idea, just with the AD chip it requred a crystal with 4x the subcarrier frequency, which for NTSC would be 14.318MHz(IIRC).
 
ttooddddyy

ttooddddyy

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mainman said:
Huh, the resistance ( resistors ) are the heart of this timer it is important.

I am not getting to teck not once did I use the words flux capacitor or Dilithium Crystal
Click to expand...

Sorry mainman I was just kidding
:eek_2:
 
B

Budd

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Reznor007 said:
Connect the output pin of the 3.579545MHz crystal to pin 6 with a wire or something. That's all you have to do really. I've built a RGB to NTSC converter myself, but it was using an AD725 instead of the Sony chip. Same basic idea, just with the AD chip it requred a crystal with 4x the subcarrier frequency, which for NTSC would be 14.318MHz(IIRC).
Click to expand...

ok, but what do I do with the other pin of the crystal? don't I have to connect it somewhere?
could you send me a picture of your converter?
 
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Budd

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ttooddddyy

ttooddddyy

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Budd said:
I have another question: can you tell me what means TTL - or what is the difference to CMOS?
Click to expand...

TTL is transistor- transistor logic, CMOS is complementary metal-oxide semiconductor, they are different types of architecture used in semiconductor design and manufacture. TTL is older tech. The same devices are usually interchangable if speed or power consumption are not critical issues.

Generally, TTL devices consume more power than an equivalent CMOS device at rest (idle), but power consumption does not increase with clock speed as rapidly as for CMOS devices. TTL uses less power and had easier design rules, but was typically slower; designers can combine CMOS and TTL devices in the same system to achieve best overall performance and economy.

Read about it here
http://en.wikipedia.org/wiki/Transistor-transistor_logic
 
ttooddddyy

ttooddddyy

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Budd said:
ok, but what do I do with the other pin of the crystal? don't I have to connect it somewhere?
could you send me a picture of your converter?
Click to expand...

it would go to ground
 
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Reznor007

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I was referring to a crystal like this(can oscillator really)

xo.jpg


1 pin goes to ground, 1 to 5V, 1 is the output to the IC, and the other is not connected.
 
Dean

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I've built many S-Video encoders from scratch using the CXA1645 chip and I use a 3.57.... oscillator for this purpose. Very easy to locate and really easy to install. Digikey has a nice selection of them including some very small ones.

Here's my encoder with a big shiny oscillator and 1645 chip:
SVidCircuit.jpg


EDIT: I should also mention that if you get a Sony PSOne monitor you can easily hook up RGB direct. Or on other monitors you can probably find where the composite input is split to RGB. I have to assume that all LCD screens need RGB to properly function.
 
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Budd

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ok, thank you all for your reply and help,
it seems to be clear now for me.

I will get the missing parts togehter, and bring that Neo Geo stuff down into the old Benz. let's hope the battery and generator will have enough power :-)
 
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