At the end of the last post I briefly mentioned you could create a Luma only cable and s-video for the Atari 8-bits. This works on any 8-bit where the Chroma & Luma are split out in the 5-pin DIN connector for the video & audio. There are some 8-bits that Atari elected NOT to separate out the Luma & Chroma unfortunately; 800XL made before August 1984, 1200XL and most 600XLs. All these computers had a single pin for just the composite connection only. There are ways to modify these computers to include chroma/luma but they all require modifying the motherboard in some form or fashion so I won't go into them here.
Here is the video/audio pin-out for the Atari 8-bits.
pin 1 > video composite + on monitor
pin 3 > audio + on monitor
pin 2 > split to composite video - & audio - on monitor
what you would do is swap the luma cable for the standard color video cable when you wanted that sharp 80 column look.
This works on any un-modified Atari with the luma/chroma pins set on or modified Atari with the luma/chroma fix.
If you are lucky enough to still have an s-video monitor you can create an s-video cable that can give you 80 column & color.
Again, you will need an Atari 8-bit where the luma & chroma pins are set on.
To create an S-video cable:
Atari pin1 > s-video pin 3
Atari pin 5 > s-video pin 4
Atari pin 2 > s-video pins 1 & 2
sound is separate line from Atari pin 3 & 2.
If it turns out the 80-column text isn't quite sharp enough just attach Atari lines 1 & 2 which be just luma, no color.
Now I haven't tested the luma only cable personally but I talked to people who have and it worked for them.
As always, this is just my suggestion. I am in no way responsible for any damage you may do to your Atari. (I don't see how you could harm our Atari making these cables but where there's a will there's a way).
There you have it. Have fun.