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Old 28 September 2013, 22:28   #1
Anemos
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Anemos RGB to SCART cable

Hello.. im on Amiga again, and this is fresh,tested and working perfect.
Test it, and stay happy amigans and atarians..
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Old 28 September 2013, 23:48   #2
prowler
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Hi Anemos,

Thanks, and welcome back to the Amiga!
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Old 29 September 2013, 13:12   #3
pandy71
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Quote:
Originally Posted by Anemos View Post
Hello.. im on Amiga again, and this is fresh,tested and working perfect.
Test it, and stay happy amigans and atarians..

Resistor values should be different (but nowadays it is not important so much)

Resistor at Pin 8 SCART can be around 1 - 2k (as this input is rated 10k impedance), Pin16 is rated as 75Ohm thus it can be something around 75 - 100 Ohm

Next info if - level at Pin 8 will be between 5.5 - 7.5V then TV should switch to 16:9 mode. (fastest way to achieve this is Zener diode (6.2 - 6.8V will be perfect).

--
Oh, please fix Pin16 source - this is TTL level input - anything higher than 5V can damage TV - this is very fast input - reason why it have TTL levels in past it was used as input for something that Amiga output as ZD (Zero Detect) - to switch between two RGB sources - crude genlock (mostly used for external teletext decoders - so called superimpose mode).

--

Ok with 510Ohm Pin16 should be safe (assuming that this is 75 Ohm input on SCART).

Last edited by pandy71; 29 September 2013 at 13:20.
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Old 29 September 2013, 17:54   #4
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Yes, you need to know the impedance. Also, not all TVs are made to spec. LCD TVs may(?) have standardized in the last years, but there is still no universally working schematic.

Except perhaps mine (see my last post which addresses this).

It's a real bid for a universal cable. I avoid the resistors and voltages with the penalty that you have to select the AV channel when you turn your Amiga on.
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Old 29 September 2013, 18:02   #5
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Quote:
Originally Posted by Photon View Post
I avoid the resistors and voltages with the penalty that you have to select the AV channel when you turn your Amiga on.
Some (most?) TVs do require a voltage on pin 16 to be able to show RGB, otherwise they will default to composite. While I can choose the input, I cannot change the input mode from Composite to RGB manually on my TV, so I would end up with a black screen if I didn't connect pin 16.
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Old 29 September 2013, 18:30   #6
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Hi
This was created to work both on LCD and CRT also.
All resistors are measured carefully for limits, and for protections.
(depending on the volt (from Amiga), and amps required to operate correctly the SCART, (0.020~0.030A).
Really has not been tested in WIDE, because I do not have.
The my LCD,is the (LG M1717A monitor-TV), and it works perfectly.
The great attention must be paid to the grounds.
Any opinion or correction welcome..
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Old 29 September 2013, 19:12   #7
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http://en.wikipedia.org/wiki/Latchup

Ideally Pin 16 should be 75ohm - however it (75 ohm impedance) can be achieved in different ways (for example dynamic impedance - current source) - with 12V on rail it can be problem - better is to reduce voltage provided to pin 16 (for example Zener diode, LED can be used also as a voltage limiter - additionally it will show power on ).

510ohm resistor with 75ohm impedance will create correct voltage but impedance must be "ohmic" type and should be constant.

IMHO fully relaying on Pin 16 as a pure resistive 75 ohm impedance is not safe assumption - it can works on 1000+1 TV but on 1002 will fail...

side comment

SCART is good example how to not design customer interfaces - bulky, low quality, with odd voltages when compared to signal levels... but it was designed in first half of the 80's and if you see schematics for TV's equipped with SCART from 80's you will see why those strange voltages was used... SCART - revenge of Frenchmen
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Old 29 September 2013, 21:21   #8
Photon
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Yes, it's horrible.

Quote:
Originally Posted by demolition View Post
Some (most?) TVs do require a voltage on pin 16 to be able to show RGB, otherwise they will default to composite. While I can choose the input, I cannot change the input mode from Composite to RGB manually on my TV, so I would end up with a black screen if I didn't connect pin 16.
Still better than connecting the voltage and damaging your new TV or Amiga the first thing you do. My post addresses the whys and wherefores of not connecting the voltage.

On one of my TVs it was a matter of pressing the AV/0 channel repeatedly to cycle through the Scart sockets and modes. On the other TVs and CRTs it worked right away.
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Old 29 September 2013, 22:37   #9
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Nice job there Anemos my friend.

I made a crosscheck with Ian Stedman's scart schematic and I only saw some minor differences (like common ground for everything) and some changed on +12V resistor values.
http://www.ianstedman.co.uk/Amiga/am...iga_scart.html

You tried Ian's and had issue or you made this from scratch?
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Old 30 September 2013, 09:30   #10
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Hi mfilos.
yep i made this from scratch..
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Old 30 September 2013, 12:52   #11
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there's a nice explanation of pin 16 at wos:
http://www.worldofspectrum.org/forum...12&postcount=8
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Old 30 September 2013, 16:49   #12
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Quote:
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there's a nice explanation of pin 16 at wos:
http://www.worldofspectrum.org/forum...12&postcount=8
http://www-user.tu-chemnitz.de/~heha...B-Umschaltung/

Even better but in German - shows real internal life of older TV's - nowadays this is implemented in different way (as signal is sampled in very fast ADC and stored in memory buffer before deinterlacing, resizing and displaying on progressive LCD or PDP display).

Older TV's usually implement RGB switch with 4066 (CMOS QUAD BILATERAL SWITCH). This is why anything higher than Vcc +0.6V can be dangerous, also modern ADC's are usually 3.3V compatible (digital part is powered sometimes lower like 2.5 or 1.8V).
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