kmod's blog

4Jan/140

Buying an oscilloscope

I guess this post is going to be the second in an unintentional two-part series on "things that I've spent an inordinate amount of time thinking about yet aren't the core of the electronics issues."  The first was about how I've improved my organizational setup, and this one is about the process of buying an entry-level oscilloscope.  I guess my hope is that it might be helpful for someone going through the same process; it's nothing fundamentally difficult about it (the different specs are well-defined and -described elsewhere), but it's certainly going to be the most exotic thing on my bench, and I found surprisingly little out there about how to actually make a choice.

My current setup

What I have currently is this oscilloscope that I bought from SparkFun (though it looks like it's sold by many other places as well), and for $60 it's actually quite handy and gets used a lot.  That said, I've started to run into some limitations with it; the most obvious is that it is limited to about 1 megasamples/sec.  That's my estimation based off an assumption of one data point per pixel it displays and the fact that the highest working resolution is 5us/div (they do let you go finer, but then the display stops working).

Does hitting that limitation a few times mean I should invest hundreds of dollars in a new scope?  Well, there are definitely ways I can imagine a "real" oscilloscope being better and more useful (larger screen, knobs instead of all buttons), but that doesn't really mean much concretely to me, so I did some searching on the internet to try to figure it out.

Which was probably a bad idea, because the internet always seems to be full of people seeking validation for their purchases; I don't think I've ever seen a comment or blog post from someone who didn't buy something and then said that they agreed with their decision, or someone who said that they opted for the more expensive choice and then regretted it.  Maybe this is an accurate portrayal and people are almost always happy buying things they want, but I think it has more to do with sample bias and the desire to justify any money spent.  But it didn't really matter, because at this point I was hooked so I decided to look around.

Oscilloscope options

After doing some searching, there seem to be a few options out there for someone looking to buy their first scope.  In increasing order of cost:

  • Don't buy one and use a multimeter
  • Get a USB/"toy" oscilloscope
  • Buy a used analog scope
  • Buy a chinese digital scope
  • Get something expensive

I did the first one (not buying anything) for a while, then did the second one when I got myself that $60 scope.  I think maybe until a few years ago the "buy used" option might have been very good, but it looks like the prices for scopes have come down enough that that wasn't an attractive option for me.

For chinese scopes, it looks like the most popular manufacturer is Rigol.  Their DS1052E (50MHz) model in particular seems extremely popular as an entry-level scope; hackers figured out that it was the same hardware as the higher-end DS1102E (100MHz) scope except for some firmware crippling, which they were able to remove.  For a while Rigol tried updating the firmware to make it "unhackable" but of course that's not a winnable battle, and it looks like they've given up and decreased the price of the DS1102E to what the DS1052E used to be ($399) so it's now quite a good deal.

The DS1102E seems to be the cheapest reasonable scope out there, is the #1 seller on Amazon, and is the one that kept on coming up in every discussion I found, so it seems like a pretty good option.

Making the decision

I looked around for any suggestions that other people have, and true to form the internet is full of advice to go big or go home.  In particular, I was curious about getting a "MSO", which is basically a scope with an integrated logic analyzer.  Rigol offers a MSO version of the DS1102E, the DS1102D, for about twice the price.  If you start considering that, though, there are a lot of other options in that price range, and a lot of people trying to convince you you have to spend even more money.  A common argument goes along the lines of "if you're going to buy the more expensive item eventually, you might as well buy it now" -- you can see that kind of thing on this blog, which is pretty much the only other example I could find of someone walking through their decision to buy a scope.

In the past I've been pretty swayed by this kind of argument -- the logic seems unassailable: if you're going to buy it anyway, don't waste your time or money on something in between.  But now I'm learning that this really isn't true: if you're having trouble with a decision like this, it's most likely because you don't know exactly what you want!  So the initial purchase is an investment in knowing how to spend your later money better.  So I decided to back from the $1k+ scopes and take stock again of why I wanted one -- I had started researching these on a whim and now I was being upsold quite high!  In the end, I realized that the main reasons to buy a scope are 1) the upside seems decently high, since based on what other people are saying they use theirs for, it has a good chance of accelerating a interest that is currently time-constrained, and 2) I feel reasonably confident that I'll get some use out of it, since I've maintained my interest in electronics for a while.

I could go on and on about how I tried to evaluate those two points and how I've misjudged them in the past (just look at my camera equipment that got used only once), but I'm going to wrap it up here and say that I bought myself the DS1102E for $399 from Amazon (prime!), and feel good about it for now though I haven't received it yet.

Update

And here it is!  This is a picture of it measuring about 200mV+-200mV of ground bias across my circuit -- not very good!  So far it's been very fun to play with, but we'll have to see about its long-term usefulness.

2014-01-04 13.56.07

Comments (0) Trackbacks (0)

No comments yet.


Leave a comment

No trackbacks yet.