need help with video detection circuit i am trying to build a circuit that detects the presence of video vs a blank screen by monitoring the r g and b outputs of a graphics card it should be able to detect the presence of a single pixel at mhz which would mean detecting a ns pulse it should also be able to tell the difference between a blank screen about mv and a dim screen say around mv oh yes it also needs to be cheap my first circuit was a dismal failure i used compariators each compariator had the input going to one of the guns the input went to a reference created by a voltage divider a potentiometer the first problem was that the compariator was way too slow i needed to get several pixels in a row before it would fire the compariators so i could have a whole screen full of text but my circuit would not detect it the second problem is that there was more noise on the reference then the smallest difference between a blank screen and a dim screen in fact the difference between completely black and completely white is only mv i am wondering if i am going to have to amplify the video signals to make this work there are faster compariators but they are expensive and require split supplies i would need to replace my quad compariator with three compariators and create a whole new power supply circuit at this point i think what i need is some sort of transistor circuit transistors are fast and cheap and should do the trick unfortunately i am way out of my league when it comes to designing transistor circuits so i am appealing to the net for help any ideas tips circuits pointers references etc would be greatly appreciated oh yes i only sample the output of this thing every second or so so i don t need a fast response time at all however i haven t found a way to take advantage of that fact thanks a lot for any help anybody might be able to give of course you will have my undying gratitude steve verity steve verity maxed on midi verity jack sns com
