While my son worked on debugging the data logger software on Windows, I tried out the Oscilloscope practice lab, using the power supply, scope, and multimeter in the lab. The first bench I sat down (Bench #1) had no power supplies, though I believe that problem will be remedied before classes start (returning the borrowed supplies from another lab or from other benches in the lab, since several had 2 power supplies).
The power supplies are quite nice, and provide very precise voltage control, but it will definitely be necessary for the students to use the power supply together with the multimeter set up as an ammeter to measure the DC current through the microphone.
I clearly needed to do more measurements between 0 and 1v, to get a better sense of the shape of the curve there, and the limitations on using the microphone at a low voltage. Had I been by myself, I might have spent more time in the lab, but we had to get my son home for an early dinner so that he could get to his theater practice on time. I’ll certainly be suggesting to the students in the write up that they use 0.1 v spacing up to 1 v, then 1v spacing up to 10v (the maximum rated voltage for the mic they’ll be using).
It was a good thing I went in before the course started to play with the equipment—I had expected some trouble with the oscilloscope, since those controls seem to be randomly organized on all digital scopes, but I had not expected trouble with the multimeter. The fancy ones in the lab have options for front or back connections of the leads, and for triggered or auto-running measurements. It took me a bit of random button pressing to figure out how to turn off the triggering and get continuous measurement.
I also put the microphone in series with a resistor and stuck a scope probe on it. It took me quite a while to get the voltage scaling and time base set reasonably on the digital scope, but I eventually managed to find all the controls I needed, and I think that I can show them to the students. Given the complexity of the user interface for the oscilloscope, I think that the simple measurements of the current vs. voltage curve and getting the scope to show both continuous waveforms (whistling or speaking) and triggering on a hand clap will be sufficient for the second lab. If students are done sooner, I could have them hook up the frequency meter and try to determine the pitch of their whistling or sustained vowel sounds.
The digital scope does allow seeing much lower frequency waveforms than my analog scope at home, and was clearly able to see 2Hz signals from moving my hand towards and away from the microphone (though 4Hz signals from faster hand movements were much clearer).
I still need to decide how many amplifier labs will use the microphone. I was figuring that the first op amp lab would do a gain of around 6 or 7 with AC coupling.
And that we’d follow that up with a power amp lab using an nFET and a pFET to make a class AB output stage after an op amp, but I’ve not wired up a power amp circuit yet, and I should do that before I order 20 copies of the transistors.
I think I’ve done all my orders except the Digikey one (and plastic bags to put the parts in). Unfortunately, it looks like WordPress.com lost 2 days worth of edits to the page of parts orders, which is going to be hellishly hard to replace. [Correction: the updates were in the autosave repository, and I was able to restore all but a few minutes work. Hooray for autosave!]