Oscilloscopes, how many channels do you need?

[Fungus]

How many channels do you need in a 'scope?

Sub-question: What do you use it for?

[Solder_Junkie]

I sometimes struggled with two channels, then when I replaced my faulty analogue scope with a Rigol DS1054Z I had enough channels.

Maybe my requirements are unusual, I am a radio amateur who likes to build transmitters and receivers. The 4 channels enable me to check keying input, receiver muting, RF envelope, DC power switching to intermediate stages, etc. Yes, it can be done a stage at a time with 2 channels, but it's easier with 4 and at the price of a DS1054Z it's a "no brainer" for what I use a scope for.

[Karel]

I voted four channels.
However, imho it depends if you use the scope for repairing (general fault finding, adjusting) or for designing.
For repairing, two channels are enough. For designing, four channels is a must.

[tggzzz]

How many channels do you need in a 'scope?

Sub-question: What do you use it for?

Depending on what you are using it for, there are three answers: 1, 2, or one more than you've got.

[tautech]

I voted four channels.
However, imho it depends if you use the scope for repairing (general fault finding, adjusting) or for designing.
For repairing, two channels are enough. For designing, four channels is a must.

+1

And either one will determine the quality of scope required.

[JoeB83]

Four channels.

EDIT Sorry, I was kinda crabby the first time I answered. Four channels, without a doubt.

After some thought, I'd really like to try out Yokogawa's 8 ch scope. Anyone here use one?

[D3f1ant]

Four.

[tszaboo]

2 might be only enough if it is an MSO. Otherwise 4 at least. 4 Ch + 16 MSO is still the best IMHO.

[daqq]

Absolutely NEED: Two. No less.
Extremely helpful: As many as possible (three being very useful, four being occasionally useful)

[tggzzz]

The answers are all meaningless, unless use-cases are specified.

For example, one of the thorniest design problems is ensuring good signal integrity under all conditions. Without good signal integrity, there is little point in doing any other fault-finding. Diagnosing the causes and then removing poor signal integrity is difficult. But it only needs one channel, optionally plus a separate external trigger.

A common design problem is looking at the relative timing of signals, often clock vs data. Here two channels are necessary.

Many problems that people claim need four channels are really debugging four digital signals - in which case you don't need four analogue channels. It is better to use two channels to ensure signal integrity and timing constraints are met, then debug in the digital domain (logic analyser or printf statements).

Low-speed differential signals can be debugged using two channels plus invert and add - provided everything is well balanced. High speed differential signals need differential probe feeding a single scope channel.

[AndyC_772]

I'd vote for three. Clock, data and chip select, or trigger condition, stimulus and response.

I sometimes connect a differential probe to my scope's 4th channel, so I can quickly switch to using it, but it's quite rare that I have all 4 analogue channels enabled together.

If I need more than three, it's usually quite a few more, and then I'll use digital channels.

[vk6zgo]

I voted for two channels,but I have four!
A Tek 7613 with two vertical plug ins,each with two channels!

I have done good work with a single channel 'scope,& in some cases,a two channel 'scope with one faulty channel,so I'm not really sure I should say I "need" two channels.

[EEVblog]

When you need 4 channel, you need 4 channels.
Probably the majority of my scope usage is single channel.

[tggzzz]

When you need 4 channel, you need 4 channels.
Probably the majority of my scope usage is single channel.

Sounds reasonable and sane.

Can you give examples of when you've needed four analogue channels? Would five have helped?

My example of when 4 analogue channels are highy desirable would be looking at complex power supply sequencing for advanced ICs, e.g. FPGAs. Such transients also require a storage scope.

[KedasProbe]

Having digital channels also reduces the chance that you will need 4 analogue channels.

[nctnico]

I'll repeat myself: once you have used a scope with 4 channels you'll never go back to a scope with 2 channels. Also note that many oscilloscopes only support the full samplerate when half the channels are on so a 2 channel scope basically becomes a 1 channel scope in such a situation.

[SeanB]

4 channels with the ability to do math (invert and add) on pairs of channels is nice, especially if the channels are able to operate at full speed when doing so. But then, even a single channel is very useful, and especially an isolated input, like on portable scopes. 4 Fully isolated channles would be the best though.

[alsetalokin4017]

Heh...

You _need_ one.
You want two.
Three would be nicer.
You'd really like to have four.
Four, plus an ext trigger, is just peachy.
Four, ext trig, and a bunch of digital channels is ... more than I can afford.

I use mine to make pretty squiggly colored lines, so that my housemate thinks I'm doing something productive with my time.  The more squiggly colored lines, the more important she thinks my work is.

[rdl]

One channel is apparently all I need. I have a DS1052E that I use constantly, but I've only used channel one a few times. I also have a 4 channel Tektronix 2247A. However, it's only been turned on a couple of times since I got the Rigol.

[rsjsouza]

In my engineering life I always used two channel oscilloscopes and sometimes I needed/wanted four. 

Because of these "sometimes" occurrences, I decided to buy a DS4k instead of a DS2k, therefore I voted four.

If four channel scopes can be had for a moderate increase in price (or moderate decrease in features), I think such tangible feature has a higher decision weight when compared to other features such as bandwidth, protocol decoding, etc. One cannot upgrade the number of channels but bandwidth and other features can be added later (especially with the modern trend of having everything upgradeable by code or firmware). 

[KL27x]

I fully admit I have used all 4 channels on my current scope only once. And only two of the signals were analog; two signals were temporary debugging signals generated by a micro. I COULD have used a logic analyzer, +- some signal conditioning on the analog lines, or even sat down and calculated out my delays. But optimizing firmware and seeing the results in real time with a 4 channel scope saved a ton of mouse clicking, switching between windows, and scrolling around between each iteration while circumventing a lot of cumbersome math.

Would a two channel MSO be better? I dunno. I have never used one.

[dom0]

One is often sufficient for simple fault tracing, but two is better. Four usually allows tinkering on an analog circuit without moving the probes for a while.

[Fungus]

Having digital channels also reduces the chance that you will need 4 analogue channels.

Yep. Quite often some of my 4 channels are showing digital signals.

2 Analog channels + some digital channels would probably be acceptable for me. Two analog plus four digital would be nice.

OTOH I really hate those stupid little clippy cables you get with MSOs. Give me ordinary probes, please!

4 analog channels works for me though, and I don't think the price of the DS1054Z can be matched by an MSO with equivalent analog capabilities.

[Howardlong]

As another poster stated, 2+16 on an MSO isn't a bad option, I'd rather have that or even 2+8 than 4+0 in most circumstances. The exception is when I'm doing switch mode power supplies when even 4 analogue channels can seem limiting.

But it depends to a large extent what you do, if you don't do much digital then the digital channels will be largely superfluous.

One further thing: remember that most 2 ch scopes have a trigger input too, which in some instances can be a reasonable compromise. A one channel scope without an external trigger offers little more than a 2.5 digit DVM for practical purposes.

Edit: meant to say, two channels can do anything a four channel can do, just not at the same time. You just need to work a little harder. Remember that 4ch scopes have only become commonplace on the average bench in the past fifteen years or so.

[Fungus]

As another poster stated, 2+16 on an MSO isn't a bad option

It seems like an awful lot to cram onto a screen.

(I haven't tried it though so what do I know).

I don't think I'd ever use 16 digital channels personally.