The 301 class went well, but far from perfectly. Despite scheduling the class for 3 hours instead of 2, I was once again overly optimistic about what I could get covered, and left a lot undone.
Of the original outline below, we only got through servos. The rest of the motor stuff – including the robot lab – didn’t make it. I’ve considered hosting another session, just to cover the rest.
What went well
I was pleased with some administrative bits:
- I thought the slides were quite good, and I was pleased to have them. I believe they let me make a lot more progress than I would have without them. They’re not quite complete, but here’s a copy as of class time.
- As usual, I used FreeMind to keep track of some initial thoughts about the class. It was helpful, but hardly a silver bullet. Probably an outline or bullet list would have been about as good – though it would have required hopping around more. Here’s a snapshot of the latest (and probably lastest) version.
- The “Please have your Arduino, IDE, and breadboard fired up and ready to go.” on the Welcome slide was good.
- By following the slide with what we were going to cover with the “introduce yourself” round, people got a chance to say what they were looking forward to and what they were already familiar with. Can’t please everybody, but it was helpful intel.
- Starting with the “what we’ll cover” slide above and bringing it back as the intro to each section (appropriately bolded/greyed) at least seemed like a good idea to me.
- Distinguishing between Arduino-specific stuff and basic electronics stuff and mentioning which we were doing on each section’s intro slide seemed appropriate.
- Distinguishing between Atmel stuff and Arduino stuff was also valuable, and I think went well.
- I think the list and organization of what all should be covered in a “control the world” class was pretty good and complete.
- Thanks to Jim H for taking some pictures.
Some content-specific stuff:
- I was pleased with introducing high- vs low-side switching. Referring back to that when discussing the two polarities of bipolar and field effect transistors was very good. (Or at least the teacher thought so.)
- I liked having some relays to pass around, and the reed switch/magnet/LEDs pass around was very nice. (Or at least the teacher thought so.)
- I was quite pleased with the analogy pictures of using transistors (both kinds) as switches.
- The labs using bipolar and field effect transistors went pretty well, and I think were valuable.
- The lab switching 120VAC with an SSR went well, despite safety squawks from one student.
- The servo lab went pretty well.
- I liked the idea of a paper lab designing a circuit with switches to run a DC motor either direction as part of H-bridge intro. Everybody at this level ought to do that exercise.
Some general stuff:
- The labs took a lot longer than I expected. Will I ever learn how to predict that?
- One of my goals was to try to make looking at datasheets less daunting by hand holding thru important parts of relevant ones. Probably mostly because I wasn’t prepared well enough with instant links to all the datasheets, I made very little headway with what I think is a valuable lesson for a class like this.
- Be sure to ask students to take pictures. Provide a camera, but try to have pictures happen even though you’re going to be way to busy to take them.
Content specific stuff:
- I went to a fair amount of trouble to have a PC/projectable scope to show PWM waveforms, but didn’t do the last 5% of the prep to be able to just pop it up, so it didn’t happen.
- I don’t think I waved a PWMed LED back and forth to show strobing and crude estimation of duty cycle. Maybe I need to make up a little dedicated demo – even with a 555 – and a really bright LED to show this off.
- I failed to have a good demo of how much better PWM is than varying voltage to an LED/resistor pair.
- Lack of prep meant I didn’t have a good demonstration of inductive spikes and snubber diodes. I failed to leave the “If you’re switching any kind of coil, always use a snubber diode!” message burned in. Shame on me.
- I was amazed that both the 2N2222s and FETs in the labs got hot with my driving and loads. I needed 330 instead of 1K series resistors with the 2N2222s. I tested this stuff on the bench. How did it not work right?
- While the SSR lab was very good, it was slightly awkward to bring and keep safe the 60W light bulbs. And a student asked: Can you still even buy these?
- I was sad that I couldn’t show the special flavor of PWM for servos on a scope.
- I should have had some kind of extra extension of each of the labs for students that got done early. (Early meaning in about the time I expected.) This is a valuable general rule for doing labs in informal classes like this.
- Having actual RC transmitter and receiver – and a scope to show the servo PWM waveforms again – would have been a plus.
- I never finished the stepper section of the slides. I suppose the good news is that I never got that far in the class, either…
- I thought the little 5V steppers (with ULN2003 drivers) would be perfect. Since they were geared down, they were not. It was annoying that I had to hand modify each of the drivers so it would plug into an Arduino easily.
- It was too bad I burned out the hard disk motor (or its contacts or something) by driving it with that 20A ESC with a 7.2V LiPo.