I have an old CRT TV (it is not a digital TV) from the 1980s and it has RF input only. Consider a circuit that comes between the video signal source and RF input. What is the simplest circuit that will rotate the image 90 degrees clockwise? What is the simplest circuit that will rotate 180 and ...
Ah, yes! The old how do you "rotate the modulated RF TV broadcast image clockwise 90-degrees" trick question!! Of course, the right answer is to turn the TV on its side. ;)
Are you expecting two diodes and three capacitors to answer this question? Realistically it's probably an RF demodulator, a fast ADC, an FPGA to read the old signal and synthesize a new one, and a DAC to construct the new video signal, and an RF modulator to shift it back up to the desired TV channel. If you want a more specific answer you might need to say whether you're working with NTSC, PAL, or SECAM TV.
Given the complexity of PAL signalling, this kind of circuit will almost certainly not fit into a Stack Exchange answer, nor would engineering it be an appropriate level of effort for such an answer. It is well within the realm of hiring an engineer with the appropriate background to design such a circuit, if it does not exist as an off-the-shelf product (note that off-the-shelf product recommendations are off-topic here)
Due to the order in which the electron gun scans and the picture data comes in, rotating means you you can only rotate a frame after an entire frame is received since display order and receive order are not the same. You can't do it on the fly. That means frame buffer which means really complicated.
It isn't a simple problem. You're getting data in line by line. You have to store each pixel until you're ready to send it out column by column (i.e. according to the new horizontal lines). You might want to correct somehow for the aspect ratio of the image not being square, and the number of lines in the image not being equal to the number of pixels per line. All in all, it's almost certainly easier to digitize it, use a few 1000 lines of Verilog to process each frame, and then reconstruct a new PAL signal from the result.
It seems like your circuit would necessarily have to include a framebuffer -- that is, you would have to store one entire frame of the image, at least, because you won't know what the first output pixel is (the new top-left corner) until you have seen the beginning of the last row of the input image (the bottom-left corner). And since you want to work with RF input, that means your device will need to (1) select and decode a channel (which means that channel-selection will move from the TV to your device), (2) rotate the image, then (3) re-encode everything as RF for the TV.
@DKNguyen Yeah. I think so. This only concept cannot work at all without some kind of digital buffering. That's why I think the whole question is funny. It's not so easy to do. Perhaps the best answer is to buy an ODROID-C2 which is designed at the outset to handle HDTV (aka Roku devices) and can run fast enough (quad CPU at 2 GHz) and has enough buffer space to get the job done. Software already exists to decode and buffer (once demoded to baseband), so just add a little more and you are done.
You're basically building something like a set-top cable box, at this point. It's not clear what your objective is, but essentially literally any other solution than the one you've chosen will be more practical -- such as e.g. buying a pre-made device that does this -- so you're going to be hard pressed to get people to give you much help with it.
If you really want an analog solution, get another TV, display the signal on that, then turn a camera on its side and point it at the new TV, and send the signal from that camera to the TV where you want the sideways picture. This might not be huge, you could use the 2 or 3 inch CRT from the viewfinder of an old camcorder, for example. But it would be a messy bodge and you'd lose some of signal fidelity.
I guess this question was a bait. But take this question as a refresher of TV technology concepts and appreciate what a marvel of engineering it actually is.
In any case, where do you expect to get a PAL signal from to test this with? Got an old NES system you want to be able to play while lying on your side in bed?
@The Photon Actually I do use it for an 8 bit computer and that is what I do use the TV for. But the 8 bit computer's hardware limits to vertical hardware smooth scrolling -this is one reason why I want to rotate the picture-so I can horizontal smooth hardware scrolling
@Z.E. Well the circuit that can do this is going to be far more powerful than an 8-bit computer. And it won't look so much like a simple circuit as a little motherboard.
Actually there is much more to that than mere frame buffering. OP doesn't want to modify his TV, just place this supposed circuit in the RF input line to the TV. This means we don't just need to buffer a single frame, we need to buffer the frames of ALL the TV channels coming in the RF signal so that his highness may comfortably choose the channel of his liking, using the TV's channel selector. Implementing this using an RF demodulator, a set of filter banks and FPGA will be equal in workload to about a PhD, I guess.
I would feel so happy if there is a simple solution-it means I can make games with smooth hardware scrolling horizontally instead of bad horizontal scrolling
@Z.E. There isn't one. If I read you the position of chess pieces from left to right, top to bottom and you can only place chess pieces from left to right, top to bottom you cannot rotate the board by 90 degrees until I have read out all the positions. You have to memorize as I read, rearrange in your head after I am done, and then start placing pieces. That is the problem you face
"I would feel so happy if there is a simple solution". Define "simple". Any solution will be orders of magnitude more complicated than your 8-bit computer signal source. A computer capable of generating video that can smoothly scroll both horizontally and vertically will be simpler than your desired "simple" solution. Is that a simple enough answer?
@Z.E. The simplest solution is the very complicated solution that The Photon outlined in in his fourth comment at the top about the FPGA, ADC, DAC, and RF modulators/demodulators. That's about as good an answer as you are going to get due to the complexity of the board.
"I do use it for an 8 bit computer and that is what I do use the TV for. But the 8 bit computer's hardware limits to vertical hardware smooth scrolling -this is one reason why I want to rotate the picture-so I can horizontal smooth hardware scrolling" - so this an 'XY' problem! (asking for X, but wanting Y). What you really want to do is improve the horizontal scrolling capability of your computer. Which 8 bit computer is it?
Your repeated repetition of "I just want the simplest solution" gives the impression that you haven't understood the comments and don't understand how television works.
I also wonder what is keeping him so determined on an 8-bit computer that he wants to rotate the display. The cheapest video rotator comes for about $ 1500 from the link which mkieth mentioned. A Raspberry Pi 4 with 4 GB RAM will come for $ 90.
Discussion on question by Z.E.: What …
Discussion on question by Z.E.: What …