cd32 rgb scart connection

[heerschop]

I want to try to add a scart rgb connector to my cd32. I have red a post about connecting a scart cable to the tp9.
This involves soldering resisters to get the right signals.

I also came across another post. In this post the scart cable is directly connected to the Sony CTA1145M chip. (see picture 1)
Is this possible without using any additional resisters?

In this post pin 11, 21, 22, 23 of the sony chip (see picture 2) are used for r,g,b and c-sync. Do I have to make a ground connection ?. If yes, where to make the ground connection ?

THanks,

Ben

[pandy71]

pin 24? see datasheet for CXA1145 - You need 2 resistors and 1 condenser for each output pin (8 resistors 75 ohm and 4 condensers - 470uF on datasheet example)
http://www.alldatasheet.com/datashee.../CXA1145M.html

[alexh]

I did this once, soldered wires to TP9 and I read that if your TV does not have an amplifier on the SCART inputs then the screen comes out at half brightness because these signals were not designed to drive a SCART cable.

Worked for me though.

[heerschop]

Thank you for your reply. I am going to try to make a scart connection on the tp9 port.
As I understand on the red, green, blue and sync connection I have to add a resistor of 47 Ohm to get the correct scart output.

tp9-> scart:
Blue -> 47 ohm -> scart pin 7
Green -> 47 ohm -> scart pin 11
Red -> 47 ohm -> scart pin 15
Sync -> 47 ohm -> scart pin 20

RGB status:
12v -> 150 Ohm (to get output of 1,5v) -> scart pin 16

There is also a connection mentioned to scart pin 8. This will allow your tv to automatically choose the scart channel.
It has to be connected by 12v with a 1kOhm resistor.
Why use a 1kOhm resistor. I measured the scart output of my dvd player and pin 8 has a 1v current.
To get a 1v current on the 12v connection a resister of 157 Ohm has to be sufficient.

Calculation:
12v -> 1,5v
U=IxR (ohms law)

12 - 1,5 = 10,5v
10,5 = 0,07 x resistor
resistor = 10,5 / 0,07 = 150 Ohm

12v -> 1,0v
U=IxR
12 - 1,0 = 11
11 = 0,07 x resistor
resistor = 11 / 0,07 = 157 Ohm

Is this the way to make a scart connection from the tp9 port.

Greeting,

Ben

[alexh]

Originally Posted by heerschop

As I understand on the red, green, blue and sync connection I have to add a resistor of 47 Ohm to get the correct scart output.

In series? I don't think so. All that would do would be to attenuate the voltage levels and make a weaker signal. AFAIR the signal on TP9 is too weak to begin with for some TV's.

Originally Posted by heerschop

Is this the way to make a scart connection from the tp9 port.

I think you have to try it. If the picture is too dark then you'll have to use an amplifying circuit.

BTW in your calculations for SCART PIN 16 & 8 you do not take into consideration the resistance of the electronics in your TV (usually rated at 75 ohm) so you need a potential divider circuit to calculate the resistances required to lower 12v or 5v to the required levels.

[pandy71]

Originally Posted by heerschop

Thank you for your reply. I am going to try to make a scart connection on the tp9 port.
As I understand on the red, green, blue and sync connection I have to add a resistor of 47 Ohm to get the correct scart output.

tp9-> scart:
Blue -> 47 ohm -> scart pin 7
Green -> 47 ohm -> scart pin 11
Red -> 47 ohm -> scart pin 15
Sync -> 47 ohm -> scart pin 20

Add active buffer for each signal - or use embedded in CX1145 (bandwith can be not enough for SHIRES)

Originally Posted by heerschop

RGB status:
12v -> 150 Ohm (to get output of 1,5v) -> scart pin 16
There is also a connection mentioned to scart pin 8. This will allow your tv to automatically choose the scart channel.
It has to be connected by 12v with a 1kOhm resistor.
Why use a 1kOhm resistor. I measured the scart output of my dvd player and pin 8 has a 1v current.
To get a 1v current on the 12v connection a resister of 157 Ohm has to be sufficient.

nope... look at the:

https://secure.wikimedia.org/wikipedia/en/wiki/SCART

Pin 16 - Fast Blanking
5V as source will be much better, use RED LED as "Zener diode" (this is FAST signal so impedance is 75 ohms - or it can be TTL - at the beginning it was TTL level signal to overlay ext RGB on TV)

Pin 8 - Function Switching
12V line by 1k resistor is ok (this is SLOW signal and it is measured on 10kohm impedance then 1kohm impedance is enough)


So best - use high bandwidth 3 channel video buffer (eg TSH345) to the TP9 or use CXA1145 avoid direct connection from TP9

[heerschop]

Originally Posted by pandy71

So best - use high bandwidth 3 channel video buffer (eg TSH345) to the TP9 or use CXA1145 avoid direct connection from TP9

Thank you for your help.
Not sure what to do now.
Maybe I try a direct connection to the CXA1145 for the red, green, blue and sync.

connect Pin 8 to 12V line by 1k Ohm resistor.

Originally Posted by pandy71

Pin 16 - Fast Blanking
5V as source will be much better, use RED LED as "Zener diode" (this is FAST signal so impedance is 75 ohms - or it can be TTL - at the beginning it was TTL level signal to overlay ext RGB on TV)

So for connecting pin 16 I have two options:
-connect Pin 16 to 5v line by this RED LED (Zener diode)
or
-connect pin 16 to 12v line by 150 Ohm resistor

Is this correct?
Sorry for asking this one more time, I just want to make sure I understand this correctly.

Greetings,
Ben

[pandy71]

Originally Posted by heerschop

connect Pin 8 to 12V line by 1k Ohm resistor.

This is perfect.

Originally Posted by heerschop

So for connecting pin 16 I have two options:
-connect Pin 16 to 5v line by this RED LED (Zener diode)
or
-connect pin 16 to 12v line by 150 Ohm resistor

Is this correct?
Sorry for asking this one more time, I just want to make sure I understand this correctly.

NP, fully understand i was also not precise then i will try answer in more clear way.

Pin 16 is "TTL" level pin with impedance approx. 75 ohms.
It is more safe to use 5V than 12V - Pin 16 expect 1 - 3V.
then You can connect to line 5V red (green, yellow - ie any color) LED that have voltage drop (diode begin conducting) approx 1.5 - 3V - typical green or new hi bright red LED are approx 2.1 - 2.2V. To limit current that flow trough LED You need resistor - 150 ohm should be ok.

so i will try to make ASCII drawings

LED
+5V o-----|_R_|---*---|>|----| GND
...........................|
...........................*-----------o connected to the Pin16

dots used as a space - In this point (*) voltage level should be approx.
1 - 3V
instead of LED, 3 silicone diodes in series like 1n4148/1n400x can be used but LED give You some visual information that circuit works.

[heerschop]

Originally Posted by pandy71

so i will try to make ASCII drawings

LED
+5V o-----|_R_|---*---|>|----| GND
...........................|
...........................*-----------o connected to the Pin16

dots used as a space - In this point (*) voltage level should be approx.
1 - 3V
instead of LED, 3 silicone diodes in series like 1n4148/1n400x can be used but LED give You some visual information that circuit works.

Thanks for the detailed explanation.

Hope I can make it work, thanks again.

Greetings,
Ben