by Klaas Robers » Tue Nov 19, 2013 2:28 am
Let me try it once more:
In order to mix or to switch analogue video signals you need to meet TWO things:
1. The video signals need to be synchroneous. That is the horizontal sync and the vertical sync both need to come on exactly the same moment.
2. If criterium 1 is Ok, then you need to remove the sync pulses of both signals, mix the remaining video signals, and place a new (also synchronous) sync signal "under" this mixed video signal. This is relatively simple. It is the task the Intersil circuit may solve, but only if the signals are synchronous, which isn't obvious.
To see if criterium 1 is Ok, you may simply mix the two signals with two resistors of say 100 ohm and connect the result to a monitor. Then you will see the result.
- If both signals are synchronous you will see the mixed video.
- If they are not synchronous you will see a mess, on which the monitor may not be able to synchronise on.
In the second case you may mix the signals with unequal strengths, e.g. use a resistor of 33 ohm in one video signal and one of 330 ohm in the other. Now the monitor will synchronise on the strongest signal (the first) and you will see the second one weakly (10%) superimposed. You will see it horizontally and vertically shifted on the screen, in some cases even slightly moving.
Please do these experiments and report us on the outcomes. Then we can try to help you to a solution. Or not, then it is impossible.
Mixing video signals is far more complicated than mixing sound channels. Colour makes it even more difficult.