Controlling Sobel edge thickness
I've done this 2 different ways in the past:


Apply a pre-blur to the image before running the Sobel operator on it. This will have the side effect of getting rid of any noise that's smaller than the blur kernel, but it will also thicken the lines you end up drawing, too.
Apply a post-process where you thicken the lines by either stamping a shape at every point that's an edge, or using some sort of dilate process.