I have one of these digital storage 'scopes I use with my lap-top, most of the time I do not need really high freq. monitoring, also the storage ability is nice.
Saves pulling my heavy Tectronix out.
http://www.syscompdesign.com/
Max.

 

the TS might find it handy for comparing ripple.

I found it useful when wishing to understand capacitance and charge rates using various resistances. Also found it useful to see with my own two eyes exactly what was being done by the waveform. I DID get along for many years without one, but having one opened doors to understanding better what's going on.

Just recently I opened an ultrasonic dog barking deterrent device and found the ultrasonic pulse was a pretty round sine wave with just a little ripple measured at 25KHz. To otherwise measure that figure I'd have needed a frequency counter. Another useful device, but I find that such machines only serve to dumb me down - and I already don't need any help with that. So learning (as I did) that the 20µS setting with a waveform covering two major divisions meant the frequency was 25KHz. I had to ASK HOW to learn how. If I had a box that said "25KHz" I would have learned nothing.

 

I have related questions. The label on the wall wart that shows the output voltage & current shows the maximum current output, right? So, the 12V 300 mA wall wart outputs a maximum of 300 mA, right?

Wall warts are OK for breadboarding or for a completed project as long as the circuit doesn't draw more than the maximum current listed on the label, right?

I took a beginners course in electronics in community college. The instructor said that the ammeter (DMM?) has to be part of the circuit in order to measure the current. I suppose that hasn't changed. So, how would you determine the maximum current needed by the circuit?

 

I have related questions. The label on the wall wart that shows the output voltage & current shows the maximum current output, right? So, the 12V 300 mA wall wart outputs a maximum of 300 mA, right?

I think it means the adapter can sustain that 300mA indefinitely without overheating and destroying itself. It's not like the silly "instantaneous horsepower" rating on a vacuum cleaner – something you can hit for a few milliseconds. But I still wouldn't choose a rating of 300mA if my load actually was 300mA. Running constantly at max is not a great idea.

Wall warts are OK for breadboarding or for a completed project as long as the circuit doesn't draw more than the maximum current listed on the label, right?

Generally, yes, as long as you rectify to DC and use a "big" capacitor for a filter. Some wall warts have this internally, some do not. There are some simple circuits that would not tolerate the ripple well. I'm thinking of a crude audio circuit, for example, where you'd hear the hum coming through.

I took a beginners course in electronics in community college. The instructor said that the ammeter (DMM?) has to be part of the circuit in order to measure the current. I suppose that hasn't changed. So, how would you determine the maximum current needed by the circuit?

Using the meter function of your meter is a valid measure. And yes, it becomes part of the circuit. Be very careful how you do this. It's good to start with your meter's highest range (often 10A) to get an idea of the current. If it comes in less than the lower range (often 200mA or 0.2A), then it's OK to switch to that lower range. If you put too much current through the meter, you can blow its fuse, or worse. Then you have to make your circuit show its maximum current. For a DC motor, you'd stall it. For something with LEDs you might have them all turn on. That sort of thing.