Here's the pulse-width modulation. The more time high (on), the higher the voltage to the motor, and the faster the feed rate on the MIG wire.

I have a couple nice digital USB oscilloscopes and signal generators that do great things on the computer (e.g., the BitScope on top and the Vellemans toward the top left of the bench picture), but more often than not, I use my cheap old dual-channel 30 MHz CRT scope, which I got on eBay for a steal. It's just so much faster to turn on and get going, as well as less likely to be damaged and less of a loss if I trash it. Of course, my students might say I'm just old-school.

Configuring and interpreting this thing isn't as straightforward as in software, though, so I have a cheatsheet.

At this point in the project (Day 1 of 2), I got a little carried away and smoked my resistance substitution box. This is a wonderful little gizmo for prototyping because it allows you to select a resistance on the fly for empirical development (i.e., hacking). I also have the equivalent for capacitance, which I did not use or smoke here.

The problem is that the insides are hidden, so you can't quite get a feel for how hard these poor resistors are working. At least, until it the magic smoke came out this time. Basically, this is what happens when you try to divide by zero in real life. Note that I killed just one resistor today, but after opening the box, I found several in distress from previous projects.

Aaaah, nice new resistors. Until the next time...

Incidentally, add a few road flares and your mom is guaranteed to get concerned when she comes to visit!.

Despite this incident, the prototyping went quickly, and I was already laying out the printed circuit board in Ultiboard by the evening.

The trick is to make sure nothing was lost or added between the schematic, the prototype, and the layout. I'm quite old-fashioned in this respect because I use markers to account for every path.

Laying out the parts. Everything except the 36VAC 2A transformer (top left) and the project box (not shown) came from my stock.