if i mix an external signal like audio with one of the r, g or b channels it will create interesting patterns like so: https://jameshconnolly.com/projects/rgb-vga-volt/audiointovideo2014.pdf
i’ve used my computer audio for this, but i’m tempted to connect up my signal generator to make even faster oscillators above ~20kHz, but i don’t want to fry anything wrt. levels.
if the receiving VGA converter runs on 5V, is it safe to mix in as long as the audio signal doesn’t exceed 5V?
also, is it safe to feed the VGA converter with bipolar signals? audio signals are bipolar, but RGB seems to be unipolar (between 0 and 5V) - is that correct?
to be within spec the colour channels of VGA should be between 0v (black) and 0.7V (full colour) so if you are being careful you should clip your signal to within this range befor sending it to vga
however in practice you will most likely be fine sending it 5v since the adapter should clip anything out of spec… (proceed at your own risk, however the vga-hdmi adapter i use is fine with this)
infact we do quite a lot of this in my analog video on breadboard class - heres a screencap of experimenting with signal generator onto/modulating vga signals:
i just tried modulating the VGA signal with a bipolar 4V (peak to peak) square wave. it seems the higher the voltage, the more color intensity i get. providing only a modest 0.7V will not give much effect, but:
not knowing anything about the VGA signal shape beforehand – the last time i looked at the raw VGA signal on the scope, the entire signal had several volts of dc offset – so that’s maybe the reason for the above effect?
that course looks sweet by the way! <3 i wish i had some extra $$ for that
