Hi, any one got any ideas how to make a screen splitter for composite video that runs from 12v so I can feed 2 video sources into the splitter and it will create one source with half the screen for each of the original sources?
Which way are you splitting the screen, top/bottom or left/right? I assume its for a composite signal too? What you'll need is each video source connected to a switch, and control the switch to send the correct output to the output at the correct time. You can get switches on chips, you can get ones designed for video work, and i think some 3-input ones if you're using component RGB. For left/right split you'll need to switch from input1 to input 2 in the middle of the scanline, and then rest back to input 1 during the horizontal blank. Im thinking a monostable triggered by the rising edge at the end of the horizontal blank and accuratly timed (no 555 ) to end halfway across the scanline. The output of that then drives the analogue switch. Not sure what it would do during the vertical blank as my minds a little hazy as to what the signal does. If you're using component video then you may have separate horiz and vert blank lines so that wouldn't be a problem. For a top/bottom split you could do the same but have the monostable triggered by the end of the vertical blank, then run til half the frame has been drawn. Not 100% sure how you could detect the end of the vertical blank though You can get sync stripper chips which separate the sync signals from a composite signal, may be useful. Alternatively, you could have a counter to count the number of lines drawn and use that to change the switch once half the lines have been drawn. Then reset during the vertical blank. (Hope some of that makes sense : ) One thing is, the circuit wiuld have to be pretty well built to avoid any interference issues. Plus the inputs signals would have to be at the same frequency. Thinking about it, each input would have to be in sync with each other, otherwise you wouldn't be able to guarantee where the second input was when you switch to it. Maybe it isnt as easy as I first thought
Well i think left and right would be good, also there will be no sync issues as the 2 sources will be the same type of camera, i will have a hunt arround and see what i can come up with, thanks for the input.
i have a quick sub question, where would one get a sync stripper chip, it would be very usefully for a project that i have.
Yeah, don't think you can just switch half way, you have to buffer it and extend each line. Since you're just splitting it in half, if that worked theoretically (isn't there an endline voltage and stuff?), you'd have the first half on half of the left screen, and the second half on the right of the right screen...right?
Actually, if the signals are synced in just the right way, all sorts of unusual tricks can be done. One might be to first draw a line from input 1 halfway across the screen, then draw a line from input 2 on the other half of the screen. Of course, stacking vertically is a lot easier, and in the days when graphics had to be manually set, the "stacking" effect can easily happen by accident. Still, it can't compare to a software-driven FPGA. But FPGA programming is not that easy.
That is a point If you want the input to be re-sized to fit just half of the screen you'd have to buffer it and somehow reduce it down. But then the aspect ratio would be messed up. My point about syncing the inputs was that when one input was starting to draw the first line of the display, the second input could be drawing any line further down the display. So when you switch to the second display it could be doing anything, drawing a line or be in the middle of a sync, resulting in a messed up display. You'd have to somehow buffer one of the inputs and adjust the delay of the buffer to get them back in sync. Gets a little more tricky when you start thinking about it some more RS used to do sync stripper chips, try CPC too. Maplin and Rapid may be worth a try. Try the LM1881, there may be others
