Forget the ‘gators, I was supposed to be doing something else.

There is an (apocryphal) tale about an engineer hired to drain a swamp. The alligators in the swamp kept interfering with the work (eating the workers,) so the engineer gets side-tracked into finding ways to fight off the ‘gators. After a while, he’s so busy finding new ways to fend off the ‘gators that he’s no longer working on the swamp.

‘Gators or transistors?

I find I’ve gone into ‘gator fighting mode here with this project. I’ve been pumping out details about little stuff, and forgotten that I was going to make a fully functional IV tracer for transistors.

I was reminded of that last night while working on the GUI for the plotter.

I looked up some pictures of transistor IV traces to get ideas for the format of the plots in my program, and realized that I had totally forgotten that it takes two variable voltages to make an IV plot of a transistor.

This whole mess started with diodes (LEDs, really) and grew from there. I’ve intended to make it fully capable of analysing transistors, but I hadn’t really thought that much about it.

It is therefore time to update the circuit, and modify the Arduino code to do it properly.

It takes two controlled signals to properly do an IV trace of a transistor.

• $I_{Base}$
• $V_{Collector}$

I can generate both using the filtered PWM method I’ve already implemented.

$I_{Base}$ can be set by varying $V_{Bias}$ as applied to the base, and then measuring the resultant current.

$V_{Collector}$ must be varied over the entire available voltage range to perform the sweeps.

A proper transistor IV trace consists of several sweeps of $V_{Collector}$ at selected $I_{Base}$, measuring the resultant $I_{Collector}$, and plotting the $V_{Collector}$ against $I_{Collector}$ - and plotting all sweeps on one chart.

Now that I’ve got my head back on straight, I’ll sketch out the circuit and modify the Arduino code as well as the GUI code.

That’s a task for another day, though. I spent too much time drawing that ‘gator up there this evening, and now it’s time for bed.