| Electronics > Projects, Designs, and Technical Stuff |
| Progressive to Interlaced Converter |
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| paul_g_787:
I am wondering if such a device exists? If not I would like to build one, after all all it has to do is switch on and off at the right time (which is the hard bit). For example, I have several CRT TVs which I still use and I want to hook up a PC to them to run Kodi clients. The TVs accept 576i 50Hz via RGBS (via SCART) PAL The PCs output 576p 50Hz via RGBS (via DSUB 15 VGA) I already made an adapter cable and I am ending up with a sliding bar effect on the screen. The image is there but the lines are sliding one after the other. So the Vsync is correct but the Hsync is twice the speed it should be. My idea so far: One could use a LM1881 to get the odd/even lines and seperate the Vsync. Then a logic circuit could be used to seperate the H sync from the H/Vsync pin to get a clean H sync signal. Then using the clean H sync, the circuit would have to switch off the sync output to ignore all the even lines on the first frame, then ignore the odd lines on the second and so on.... While the sync is turned off, 3 transistors could be used to ground the RGB lines to turn them off at the same time as the ignored lines. I think this would be a useful device, it would be great to support 480p too for NTSC compatibility but we only use PAL on CRTs in the UK. Is there a microcontroller that can switch fast enough for this? or perhaps dedicated harware is best? Any thoughts on this? |
| T3sl4co1l:
It's not so much the speed (analog TV is only ~MHz BW) as the storage. A frame is, what, a few hundred kB? You need to store at least half that (one full field), plus an extra one half line. Play back the first line of the first field, then the just-recorded line of the current field (which will have finished receiving just in time to transmit; more likely, you'll store the whole line and not mind the extra half-line requirement), then the second line, then the just-recorded second line, then... Obviously, alternating down as you go, at double the output bandwidth. Mid-tier ARM MCUs have about as much RAM onboard, give or take exact bandwidth, bit depth and encoding. And they run in the 160MHz range which is enough for a dozen or so instructions per sample, which may facilitate some minor encoding to save on space. Figure about $10 for the chip, and, who knows, several months to write it..? Might be easier to write on an FPGA, a mid-tier one of which might run $20-40, would have enough block RAM onboard to hold a frame or so, and way more than enough logic to handle any decoding and encoding you might need to support the video format and to save RAM. The PC can't just use a capture card? Tim |
| Benta:
The LM1881 will only give you a correct even/odd output if it is fed with interlaced video. That's not the case in your scenario. |
| james_s:
You used to be able to get VGA to TV converter boxes for around $25, can you not still get those? Some PC video cards can be tweaked to produce nonstandard timing too. Another option is a Raspberri Pi, it has a composite output and a Kodi client. |
| soldar:
I believe a lot of those "de-interlacers" merely dropped one field and interpolated the other field. |
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