Technical Illustration: How to Draw Crisscrossing Circuit Wires with Adobe Illustrator

David Herrick
TCC Guest Writer & Sr. Illustrator
The simplest way to indicate a criss-cross in a wiring diagram (or anything, really) using Adobe Illustrator.
If you have a sketch or diagram already, scan it and save the scan as a JPEG or PNG, then open a new document in Adobe Illustrator.
Choose “place” from the file menu and place the scanned image. It’s best to keep the scanned image on a separate layer than the art that you will be creating, so create a new layer for your artwork (from menu bar – window> layers), then lock the 1st layer so you don’t accidentally select your scanned image as you are working. I usually select ‘dim images to 50%’ so it is easier to see the art that I am building on top of layer 1 (see diagram 1 below).

 
Select layer 2, then select the appropriate tool from the tool menu. In most cases, this will be either the pen, ellipse, rectangle or rounded rectangle tool. Draw your shape and make the shape an unfilled stroke (menu bar – window>stroke), and the thinnest stroke weight possible so you can avoid obscuring the placed image that you are using as a template (I usually use .25 points).
Consider leaving the lines black at this point, you can change their color later, although if you’ll be using many different colors in your diagram, it may be best to indicate the colors as you create them.
Draw all the lines that you need, using the scanned image as a guide. If one section of a ruled line needs to go over/under several times, you’ll need to add selection points along the run using the pen tool. Add selection points in-between the over/under passes.
After you have drawn all the ruled lines, you can increase their line width as needed using the stroke menu (window>stroke). Then, making sure that none of the ruled lines on your working layer are locked, select ‘all’, select ‘object>group’, then copy and paste behind (edit> paste in back).
Change the color from black to 100% yellow and increase the stroke width. Making the ruled lines 100% yellow will allow you to see them against the placed scan, and see exactly how thick you are the increasing their width. I would suggest no more than a 2 point rule at this point so you don’t obscure your scanned template (see diagram 2 below). You’ll need to see your scan for the over/under information.

Now, here’s the fun part… creating the criss-cross.
You should be able to see your scan to know which sections will indicate the overpasses. Using the direct-selection tool (the hollow arrow on the top right of the toolbox), do a marquis selection across all the desired sections (see diagram 3 below), pressing down the shift key so you can select multiple sections.

Then, cut, DE-SELECT ALL, and paste in front. You’ll see that both the 100% black .25 point rules and the yellow 2 point rules will jump to the top of all the uncut sections, giving the appearance of the over/under look that you want (see diagram 4 below).

After you have adjusted all the sections, you can change colors and line widths by select>same stroke color and/or select>same stroke width (see diagram 5 below).

After you are sure that all the crossings are correct, remove the scan layer by unlocking and deleting the placed scan. In this example, I have increased the black stroke’s width to 7 points, and the white stroke to 13 points (see diagram 6 below).

The last thing to do is to eliminate any ‘stray points’ that might be there, as these can create problems. A stray point is a single selection point with no connecting ruled line. Go to select>object>stray points, then press delete or backspace on your keyboard. Save the document as an EPS or PDF if you will be exporting it as a placed graphic in another application.
Check out David’s superior work at www.davidherrick.com