Silly question about oscilloscopes

[eloso]

Not a silly question !

Neither is it one that really anyone is really qualified to advise on apart from the OP himself who knows what he wants to do - it really is such an individual thing.   But what we can do perhaps is just describe our own reasoning for owning our own scopes and which kind of scope suits us.

I would be lost without my Rigol DSO2072A (upgraded to DSO2302A). I do lots of digital, general analogue and RF circuitry.  I design my own and am often fixing other peoples designs, be they consumer items or more specialist.

I would prefer a good fast 2 channel scope over a more mediocre 4 channel scope anytime, despite digital being my thing.  Memory depth is crucial to me too.

When I want to analyse lots of digital signals all together at the same time I rarely am doing it from the point of view of the examining quality of the waveform - usually its a digital encoding thing and for those jobs I use my cheap and cheerful logic analyser with 16 inputs it usually covers my needs.

On the other hand to examine the qualitative characteristics of digital signals I never need more than two channels. Occasionally I use one for triggering and am looking at the other trace to look for abnormalities.  Following that I may stick with the same trigger config but probe a different line alongside the previous.  And  then I might do this again.  i.e. my 2 channel scope is being used as say a four channel scope but not all channels simultaneously if you know what I mean.   

The beauty of modern scopes unlike the behemoths of my youth is the ability to look back in time, not just in the here and now.  It is also to freeze the moment in a single shot or to average a signal to get rid of noise.   Nowadays we can set triggers and examine the waveform as it was prior to the trigger event.  Wow – really useful. 

We all have different needs but just in case it helps, here are the things I have used a scope for recently listed in no particular order. Some of them you could do with a multimeter, or a logic analyser, some of them only a ‘scope.

1.   Check for the presence of the right kind of signals on SPI, I2C and UARTs.   Quick and dirty just to make sure the software is driving the lines that I think it should be, and that it is doing so at more or less the right times/intervals and that the signals have all the appearance of reasonable quality and proper polarity ones.
2.   Check polarity of GPIO inputs and outputs.
3.   Measure RF power output accurately of a commercial transceiver.
4.   Measure overshoot of RF being fed into an amplifier that was tripping out with an overload indication.
5.   Look at and measure signals on an RF mixer circuit as part of a fault finding process.
6.   Set up a mechanical bug key so that its relative timings (mark space ratio of the dots for example)  are correct. Very, very slow timebase.
7.   Check voltage transients on power supply that kept tripping.
8.   Using a current sense resistor and a differential probe measure inrush current accurately for a device that was tripping its power supply.
9.   Monitor output from an optical sensor.
10  Check the level of back-emf from a relay coil to ensure it doesn’t exceed safe limits.
10.   Look at key clicks on TX output.
11.   Quick and dirty frequency counter to ensure xtal oscillator is running on its fundamental.
12. Do quick and dirty FFT to check the level of the third harmonic (not a strong point of most scopes but it can be useful)
13. Determine the precise trigger point of some comparators
14. Design and debug some op amp circuits being used to generate +- 40V ramp testing signals for another circuit under test.
15. check for clipping on some AF signals.
16 Set audio levels precisely to match an amplifier's input range.

And more of the above that I have forgotton about.

One important thing to note is that a modern oscilloscope is a fun instrument and to me has always had a kind of magic about it.  (Mind you, so easily pleased am I that even a humble DMM has a magic about also!)   You don't need to have one - but if you want one and have the cash then get one and have a play  .

Careful though, this might be the start of the slippery slope leading to Test Equipment Anonymous....

Eloso