Graphics, sound and multimedia • Re: Adding a SCART/RGB input to RPi5

Thank you all so much for the help.

I very much doubt a simple ADC will be enough. At least one of those video signals will have line and frame sync signals that will need to be extracted and processed.

Yes, you're right, I forgot to add a connection for the composite line. I'm not sure whether to attach that direct to the GPIO, which makes handling V/H sync easier or via an ADC (or something) so that I could potentially read a video stream over composite, though this has added complications I think. In either case, I think I still need 75ohms to ground and something (100ohms?) going into the GPIO/ADC input.

Plus SCART isn't just RGB. Depending on the source device it could be RGB, it could be CVBs, it could be S-Video or a combination. It's also nothing more than a standard for the physical connector not for the signals being carried.

I'm planning to start with RGB devices and go from there but yes, absolutely.

No. MCP3008 is far too slow to digitise video. Even if you did have a proper video ADC, interfacing it to the GPIO header would be difficult as the required data rate is very high. USB would be much better suited to this.

Find a USB video capture device that supports RGB and has Arm Linux drivers.

I'm trying to see if it's possible to use the RPi as an upscaler. I know there are reasons why a Pi isn't the best option for this but I'd like to see what's possible using the HVS module via libdrm for the output and DMA for the input. Perhaps just a frame or two of latency but with a lot of flexibility over how the output is scaled and rotated. But, in any case, USB is too slow.

What about using the built in ADC on a Pico and using eight digital outputs to transfer the data to the RPi5 a byte at a time? In which case, I'd still need to work out what the proper resistor combination is.

You also need black level clamps on analogue video signals before digitising them.

Is this necessary for RGB? I thought a black level clamp was something needed for composite signals?

Statistics: Posted by Moocrow — Sun Aug 11, 2024 8:14 pm

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