Recently acquired my first oscilloscope (Siglent SDS804x HD with license key "hack" applied) and I've been playing around viewing various waveforms with it. I have a simple microcrontroller circuit generating a 900Hz rectified sine wave, and it passes through a capacitor to remove DC bias.
I'm confused about what I'm looking at when I plug it into my scope. It seems like my audio signal is somehow being represented in the "negative space" of these traces. As I change my code (different freq, different wave, etc) the negative space changes to match. What I expected to see was something akin to this image: A series of square-ish pulses of different width.
What I would eventually like to figure a way to demodulate the audio wave and display it on my scope as its own trace, then play around by analyzing it independently of the PWM. I'm sure that somewhere in all the math functions on this scope, there's a way to achieve that, but I haven't found it yet.
your sound is a 900Hz sine wave. i dont see your scope mentioning 900Hz anywhere. to represent a 900hz sinewave, you need about 4 samples at least, to represent a sine-ish-curve. i.e. 4 x900hz sampling rate. but also 4 pixels on screen to repseent the curve.
But not looking at the numbers, an image like that could happen when the data which needs to be presented has more datapoints than the amount of pixels the display is wide (maybe your scope is 1024 pixels wide?) it could be the oscilloscope is just picking 1024 samples out of the millions of datapoints, and drawing lines between them(which will be vertical lines). That's one way to get strange representations. What i see on the osccilliscope is countless vertical lines together making it look like a fill.
To check if that's it, you can zoom-in on the x-axis only, and check if the pattern changes(and eventually shows your sine wave)