Automatic voltage scaling with op-amp?

I'm afraid your LM311s are not opamps but voltage comparators. You can see the datasheet here

As for gain scaling of video, the video level is not a good way to do it since its hard to tell what levels should be until you get a peak white. The sync amplitude is very reliable because its always there at

300mV (OK, 286mV to be spot on). Continuously variable AGC would be a little harder than range detecting but certainly doable. If you don't have sync on the video, it will get more interesting. Personally, I just fix the problem with the video since widely varying levels implies faulty transmission lines/terminations which will muck it up anyway. Fixing reflections from faulty cables automatically is possible but way beyond simple opamps. GG

The LM311 is a comparator, not an op amp. It switches between logic 1 and logic 0 depending on the inputs.

Good luck Chris

LM324 is an opamp on Valium. You need something much faster for video. National, TI, Maxim, Analog devices and other have good amps for reasonable prices. Check the MFRs websites and Digi-Key, Mouser ...

For your purposes I think I would do it as a multi-input switch with the proper gain scaling for each input. GG

Not exactly sure what the difference is. I think one of these other chips might be an op-amp, it's an LM324.

It isn't a problem with the video really. I'm hooking up arcade PCBs to an old RGB monitor which is able to sync down to the 15khz. Some of the boards I have output up to 3V, some output less than 0.5V. They all work great hooked up to the monitor that is in their dedicated cabinet. I just wanted something that could automatically adjust the levels while it's on my test bench.

I guess what I was hoping for was a schematic that showed how to have a input voltage, a reference to the input's max, and a reference to the output's max, and it would do the scaling. Can that be made with an LM324?

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On Monday 20 September 2004 12:16 pm, Glenn Gundlach did deign to grace us with the following:

I second this. I've worked with video games before, and there are only a couple of attenuations you'd need.

And 15 KHz is the sync rate, but the video goes up to 6 MHZ. Lowering the bandwidth spreads out the pixels - their edges are rise time, you know. :-)

It's cool watching live TV video on a scope - it's like an edge-on view of the screen, where amplitude is intensigy - it's almost 3D, with the proper medication, of course. ;-)

Good Luck! Rich

Even if you use a video opamp it will not be able to *automatically* correct the gain. you will need a VCA with the appropriate bandwidth and a circuit to determine the level of the video signal. This is not a trivial task. If you do not need amplification, a passive adjustable damping pad could be manually adjusted, so the following stage is not overloaded.

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They've been paying me 28 years to look at scopes of video of almost every variety, from the lowly VHS up to HD film to video (telecine). What is real cool is to see a frame rate background, light at the top of the screen and dark at the bottom. Superimposed text is readable on both the scope and the pix monitor. I've never seen it but I have it on good authority that the guys at NBC varied the chroma and hue to say 'Merry Christmas' on the vectorscope one year. GG