Muff's Modules & More

andrewF · Posted: Fri Oct 07, 2011 4:03 am Post subject: Vector rescanning tips....please!

I have been trying out the tv-scope cct here - http://www.electronixandmore.com/project/14.html
this one -

Can get decent looking sawtooths for x&y (had to short out the cap between lm1881 pin3 and pin 2 of the Y channel 555).

but cannot see any kind of image on the scope beyond waveforms.
Does it require some pretty fine tuning of the X and Y trimpots to get an image? Bit like vertical hold and horizontal on a regular tv?

I realise the intensity has to be turned way down for the Z input to have any effect, but it seems to be doing nothing, testing the Z input with a LFO shows that it does work.
It seems I need to amplify the Z signal or can I use the Y output on the VSG?

Once i get this stage working correctly, is it 'simply' a matter of mixing ramps and other CV with the X&Y sawtooths to get vector rescanning? Or should the ramsp be from oscillators sync'd to the original signal getting sync signals from my LZX modules?

oh so many questions - sorry, i'll stop for now

andrewF

daverj · Posted: Fri Oct 07, 2011 8:14 am Post subject:

The 470K and .1 going to pin 2 of the 555 are so it will oscillate when there's no video input. If there will always be video in then you could eliminate those parts and just tie the 1881 directly to the 555s.

Using the scope as a regular scope you should be able to view the ramps and tune them. Once they look good then connect them as X/Y and you should see a basic raster on the screen. If it looks "folded" or uneven brightness, then either the ramps aren't pure ramps or the scope has limited bandwidth in the X (horizontal) axis.

The Z input on most scopes does usually require amplification. And often needs to be negative.

Once X/Y and Z are all working you should see a basic video image on the scope (raster plus intensity). After that what you want to play with is to run the ramps through various other modules, mixing or modulating with other oscillators, before going to the X/Y inputs. That will give you control over the shape of the raster. You also want to mix video into the ramps to offset the raster using the intensity info from the video. That gives the classic Rutt-Etra style of video deflection.

lizlarsen · Posted: Fri Oct 07, 2011 10:18 am Post subject:

Yes, everything Dave said is correct -- you're doing it right ("Y/Luma" output from the Video Sync Generator module to the "Z" input on the scope.) But you'll need to amplify the signal, it sounds like (and possibly invert the "Y/Luma" signal going to "Z" as well.) It does depend on the monitor. The Tektronix 620 and 606A monitors I just got do not require nearly as much amplification as the Z input on my oscilloscope does (and the beam is brighter too.) A super simple amplifier circuit using LM6172 or other video op-amp should be easy for you to DIY (PM me if you need help with the circuit.)

After that it's just a matter of messing with what you're sending to XYZ and applying VCAs, modulation, etc. A matrix mixer setup works great for this.

lizlarsen · Posted: Fri Oct 07, 2011 10:22 am Post subject:

lizlarsen · Posted: Fri Oct 07, 2011 10:28 am Post subject:

andrewF · Posted: Fri Oct 07, 2011 8:25 pm Post subject:

Thanks Dave and Lars
I will keep working on this, was just unsure of the best route to take. Probably should plan a proper panel rather than ending up with a bunch of random veroboards in a cardboard box (again)

andrewF · Posted: Sat Oct 08, 2011 5:29 am Post subject:

here's another project converting video to 'scope' (well a crt from a scope)

http://www.rhunt.f9.co.uk/Electronics/Video/Video_Page1.htm