Using an oscilloscope as a waveform generator

[Gordonjcp]

Here's a wee video clip where I'm using an LDR, a resistor and a battery in conjuction with an oscilloscope with a cardboard mask over the tube to generate an arbitrary repeating waveform.  I fed it into my Polysix's VCF CV input while it was playing an arpeggio.
Oscilloscope as waveform generator

[Circuitbenders]

I'm trying to get my head around exactly whats going on there.

It certainly looks and sounds like the type of thing i end up spending hours fiddling with for no apparent reason 

[moordenaar]

FUK YEAH ! Now that is sweet ! Could you explain a little more ? Now I know what I'm going to use that old crappy single channel in the corner.

[Gordonjcp]

Cardboard mask in the shape of the waveform you want on the tube face.  It's probably best to get the mask right onto the glass - most 'scope tubes have rimbands so there is little risk of implosion but be careful!

LDR connected as the lower leg of a voltage divider, powered by a battery.  I used a pot for the upper leg so I could set the idle current.

Voltage across LDR fed to Y input, with Y pos and Y gain set appropriately - experiment until you get the best results.

X sweep set to a low speed - my 'scope goes down to 200ms/div - and aim the LDR at the screen.  When the spot appears over the mask, the light falling on the LDR will cause its resistance to drop, pulling the spot down again.  If everything is all working perfectly  (there's a lot of fiddling, and you need a dark room or a cardboard hood over the 'scope tube face) the spot should track the top of the cardboard mask.