Propeller-I Video Flicker
sobakava
Posts: 32
Hi everybody.
I've been using my own Parallax board with small analog monitors for a long time. A couple weeks ago I discovered that my composite video on the screen might look much better somehow.
Please check the video :
https://vimeo.com/87603982
At the beginning video quality is pretty good for me. There are shadows but I totally don't mind. But at 00:35, I'm resetting the Propeller by pressing F11 on the Propeller Tool, reloading the same firmware. Then I get my usual flickering image. My PCB is a double layer board and it is powered from LM2576 switching regulator. I can see there is less than 20mVpp noise on the VCC pins of the propeller. This two flickering and non flickering modes appears to be happening in random. I've never seen switch between modes without a reset.
What causes this in my design?
Thank you all.
I've been using my own Parallax board with small analog monitors for a long time. A couple weeks ago I discovered that my composite video on the screen might look much better somehow.
Please check the video :
https://vimeo.com/87603982
At the beginning video quality is pretty good for me. There are shadows but I totally don't mind. But at 00:35, I'm resetting the Propeller by pressing F11 on the Propeller Tool, reloading the same firmware. Then I get my usual flickering image. My PCB is a double layer board and it is powered from LM2576 switching regulator. I can see there is less than 20mVpp noise on the VCC pins of the propeller. This two flickering and non flickering modes appears to be happening in random. I've never seen switch between modes without a reset.
What causes this in my design?
Thank you all.
Comments
From the looks of it, your display is having some trouble locking on to the signal consistently.
You might resolve this by changing the number of scanlines in your display by one (take out a blank one)
Better to write the driver to not alternate phase. Look at my Nyan Cat project here (google, as I am on mobile and do not have time for a link right now) for one example of a driver that does not alternate color phase. Eric Ball, the author of that code, has done a couple others, as have I. You would need to adapt that code to your display requirements, or modify what you are using to give fized color phase.
Look for the colorburst timing relative to the scan line.
Does your display accept S-video? If so, that is a pretty great solution which only requires a different video circuit and a small change to VCFG.
Unfortunately my displays ( several kind of brands ) have no SVIDEO inputs.
Frankly I have no idea where to look for changing number of scanlines. In TV driver there are sntsc and spal lines. I tried to change them experimentally. Seems nothing changes. And I also don't know where to look for colorburst timing or what to change.