re need help with video detection circuit verity jack sns com steve verity writes 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 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 in order to get the ns response time you need you are better off going to an ecl slicer which can run off a single or v supply you just need to bias or do some level shifting perhaps to get it in the range check out the ecl k books for a simple cheap solution dino inqmind bison mb ca the inquiring mind bbs winnipeg manitoba
