[Coco] CoCo 3 RGB to SCART video, then converted to HDMI

[Salvador Garcia]

 but, well, if you don't believe me, I'm not really concerned,
believe what you want,

 
He said that in a jokingly affectionate manner and was a humorous way to request pictures. A tendency here is that we all like (love?) to see pictures (and when possible videos) of others' projects and it seems as though your project caused well deserved attention for its ingenious simplicity. Salvador
 
 
-----Original Message-----
From: Barry Nelson <barry.nelson at amobiledevice.com>
To: coco <coco at maltedmedia.com>
Sent: Thu, Apr 30, 2015 5:17 pm
Subject: Re: [Coco] CoCo 3 RGB to SCART video, then converted to HDMI


Responding to some of the comments…
First, I will try to post pictures and a
video soon, but, well, if you don't believe me, I'm not really concerned,
believe what you want, I'm just trying to share the information, but my setup,
at least with the converter I have, works very well. As to using pins 8 & 9,
there are a few issues:

1) The signal level is very low, less than 2V peak to
peak. (It is NOT TTL)
2) The polarity is positive instead of negative.
3) The
signal on those pins is a simple square wave, it has no "back porch" or "front
porch" levels on the vertical sync line.
4) Their timing and pulse shape may be
ok for a CM8 monitor, but nothing else seems to like them.

I am sure all these
issues could be resolved with the right circuitry and time, but why complicate
things needlessly?

The sync signals on the composite video line have the right
timing and include the front and back porch levels, and my SCART converter seems
to happily ignore the other "stuff" on that line when it is in RGB mode. Maybe
an LM1881 might provide a cleaner signal, but it does not seem to be necessary
as the picture is clean and stable.

I have no plans to manufacture cables at
this time, but anyone else is welcome to use the pinout I provided and make
their own cable.

I got the idea for this after attempting a couple of other
solutions, and researching the the signals and voltage level output from the
CoCo. I found that the RGB signal levels and timing matched almost exactly what
a 480i SCART signal looked like, and the voltage levels and timing on the
composite video line were a match for the sync pin on the SCART connector.
Interestingly, a side effect of this is that if you disconnect the 5V line from
the 100 ohm resistor, the SCART switches off the RGB signals and uses the
composite video instead, so with one video connection you can actually switch
from RGB monitor mode to TV mode by toggling this voltage on or off.

On Apr 30,
2015, at 10:07 AM, coco-request at maltedmedia.com wrote:

> Date: Thu, 30 Apr 2015
08:37:57 -0500
> From: Dave Philipsen <dave at davebiz.com>
> To: CoCoList for
Color Computer Enthusiasts <coco at maltedmedia.com>
> Subject: Re: [Coco] CoCo 3
RGB to SCART video, then converted to HDMI
> Message-ID:
<55423035.2060703 at davebiz.com>
> Content-Type: text/plain; charset=utf-8;
format=flowed
> 
> If you have a problem with a circuit that just needs the sync
signal(s) 
> from a composite video source there is an inexpensive chip that
will 
> strip the sync for you.  It is an LM1881.
> 
> Dave Philipsen
> 
> 
> On
4/30/2015 6:09 AM, Steven Hirsch wrote:
>> On Thu, 30 Apr 2015, Barry Nelson
wrote:
>> 
>>> I have conducted an experiment and it worked! I wired the CoCo
3's 
>>> RGB video lines from the connector on the bottom of the computer to

>>> the RGB lines in an SCART connector. I connected the audio from the 
>>>
CoCo connector to the left and right audio on the SCART connector. I 
>>>
connected the CoCo 3's composite video to the composite video/sync on 
>>> the
SCART connector and I connected +5V to a 100 ohm resistor 
>>> connected to the
"fast switching" pin on the SCART connector. I then 
>>> plugged the SCART video
connector into my SCART --> HDMI converter, 
>>> which I plugged into my TV.
Viola! Perfect RGB video up scaled to 1080P.
>> 
>> From my experience with
other classic machines, use of composite video 
>> as composite sync for SCART
is hit or miss.  Glad it worked out for you!
>> 
>> Would love to see some
photos of 80-column text mode.
>> 
>> 
>> 
> 
> 
> 
>
------------------------------
> 
> Date: Thu, 30 Apr 2015 09:49:05 -0400
>
From: Michael Rowen <mike at borncoco.com>
> To: CoCoList for Color Computer
Enthusiasts <coco at maltedmedia.com>
> Subject: Re: [Coco] CoCo 3 RGB to SCART
video, then converted to HDMI
> Message-ID:
<rlrrdi1gf0sx336815c38tag.1430401745551 at email.android.com>
> Content-Type:
text/plain; charset=utf-8
> 
> I would think the coco RGB vertical/horizontal
(pins 8 &9) inverted through a 74LS02 (Nor gate) would work to the sync line on
the scart. This is very cool. I'm going to try this myself.
> 
> This device
also converts composite to HDMI. With Ed's awesome composite boards for the
Coco2, might do a decent job for a Coco2 as well.
> 
> I found several YouTube
vids for this same device used with various gaming consoles via scart. Just
search for scart.
> 
> -Mike


-- 
Coco mailing
list
Coco at maltedmedia.com
https://pairlist5.pair.net/mailman/listinfo/coco