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Choosing a scope
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Please be positive and constructive with your questions and comments.

Choosing a scope

by bbbad on Mon Aug 24, 2009 11:46 am

Hi
I'm a teacher with a growing interest in electronics and robotics. I want to add a little more electronic theory to my class and start a robotics/electronics club. I know basic theory, but I'm lacking in practical experience. I've been thinking about buying an oscilloscope so I can show the students some of the transient effects and as an analysis / learning tool for the club. I've spent the afternoon looking at stuff on the internet and there are a lot of general rules of thumb and how to use articles, but what I need is "what to buy" advice.
I searched the forum, but the only suggestion was...
"...you're going to want an oscilloscope. Tektronix makes a full line from entry to "metrology lab standard" grade. Consider a Tek TDS 2024b."

That's a $2400 machine, do I have to spend that kind of money? Price is a concern as I'll have to buy the scope myself.
I want to be able to show kids switch bounce, measure the flash rate of an LED accurately, see the waveform of an RC circuit, see ripple and the effect of a cap on it. It will have to be fairly simple projects in the beginning, but over time I would like them to be able to build some fairly sophisticated analog and digital projects.
So what do I need? I've rejected the sound card oscilloscope solutions as they seem too crude, too bad though, they're cheap enough that every student could have one, but what else?
Storage is a must and at least 2 channels, but what bandwidth and sampling rates will I need to provide good examples of how circuits and components behave?
Are any of the PC peripherals really useful?
If so are their kits I could buy and assemble?
Can I pickup a scope on eBay that will do the job for a reasonable price? What do I look for?
Any recommendations would be appreciated.
bbbad
 
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Re: Choosing a scope

by zener on Mon Aug 24, 2009 1:44 pm

Someone had mentioned this one:

http://www.saelig.com/product/PSSA002.htm

I seem to remember it was even cheaper a few months ago. I haven't used that one though.

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Re: Choosing a scope

by eil on Mon Aug 24, 2009 9:10 pm

viewtopic.php?f=8&t=7755

viewtopic.php?f=8&t=9598

viewtopic.php?f=8&t=7486

Short story: A used Tektronix 465B is the best bang for the buck

Although if storage is an absolute must, that bumps up the price a lot higher. Showing waveforms is extremely helpful, but once the students understand the basics, you can just draw the waves that a "normal" scope can't show (i.e., switch bounce). In fact, it may be more educational to discuss why a standard scope can't show something like switch bounce easily.
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Re: Choosing a scope

by bbbad on Tue Aug 25, 2009 9:53 am

Thanks for the response.
...best bang for the buck: tektronix 465B

There are still plenty of them available too. I have some time before I actually need the scope, so I'll watch the auctions to see what turns up.
bbbad
 
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Re: Choosing a scope

by sirket on Thu Aug 27, 2009 9:48 am

You need to decide what you want to use the scope for. If you are doing higher-speed logic with 4 probes- then you need a 200MHz Tektronix 2024B (Or preferably something without the god-awful passive matrix display that scope has- I loathe the display on my 2024B).

From the sound of it- you just want to see what simple, slow speed waveforms look like- the Saelig scope mentioned earlier is more than capable of doing that, and doing it well. The Tektronix 465B (I also have a 2465A- similar- faster, but still analog) is a great scope- but it's a lot easier to demonstrate waveforms when you can store them and just display it.
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Re: Choosing a scope

by mkwired on Thu Aug 27, 2009 10:27 am

Check out the Rigol DS1052E.

Review of the Rigol DS1052E Oscilloscope
http://www.youtube.com/watch?v=kdjpbWLi7UI

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Re: Choosing a scope

by zener on Thu Aug 27, 2009 1:21 pm

eil wrote:Short story: A used Tektronix 465B is the best bang for the buck

This used to be the answer, but times have changed. We have a few here, and if it was up to me they would be in a box shipping to you (or anyone). The pots get worn out and you can never get them to sit on any particular line. Can cause insanity. And they are the size of a small car and weigh only slightly less. The myth that analog scopes can catch transients that digital scopes cannot has long since been disproven. My boss raves about these scopes but no one here will use one when there is a digital scope available, we just don't have time to screw around with it and there is no bench space for it. IMHO. I would ask him if he will sell one to you but he just likes to see them piled up on the shelf for some reason.

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Re: Choosing a scope

by eil on Thu Aug 27, 2009 8:51 pm

Zener wrote:
eil wrote:Short story: A used Tektronix 465B is the best bang for the buck

This used to be the answer, but times have changed. We have a few here, and if it was up to me they would be in a box shipping to you (or anyone).


If we were talking about a scope for frequent or "serious" use, sure, you probably want something better (or at least newer) than a 465B. But for people who think they want a scope, but don't know where to start or what features they need, the 465B is my (and others') stock recommendation because they're relatively easy to find and cost a fraction of a digital scope of any age.
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Re: Choosing a scope

by zener on Thu Aug 27, 2009 9:25 pm

Yeah, it looks like they are going for 100.00 including shipping on Ebay so that is pretty cheap. Then you have to buy probes. But I would say you are getting what you are paying for there. I would really like to hear from anyone who has tried that Saelig scope.

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Re: Choosing a scope

by Amberwolf on Fri Aug 28, 2009 3:26 am

Zener wrote:
eil wrote:Short story: A used Tektronix 465B is the best bang for the buck

<snip>And they are the size of a small car and weigh only slightly less.

No, *my* scope is the size of a small car, and weighs only slightly *more*:
Image
Since it's a 531A running vacuum tubes, it runs about as hot as a car, too. ;)

But it works fine for my purposes, since I don't need it to be calibrated perfectly--a general idea of a range of voltage and frequency is close enough, and being able to see the shape of the waveform.

If those limitations aren't a problem, you can probably find them around cheap enough. (mine was given to me when a friend had to move suddenly).
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Re: Choosing a scope

by brain_recall on Fri Aug 28, 2009 7:42 pm

Amberwolf wrote:But it works fine for my purposes, since I don't need it to be calibrated perfectly--a general idea of a range of voltage and frequency is close enough, and being able to see the shape of the waveform.

If those limitations aren't a problem, you can probably find them around cheap enough.


Very true. I picked up an "untested and uncalibrated" Tektronix 2215A off eBay for $50 without probes. Best money I ever spent.
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Re: Choosing a scope

by SiliconFarmer on Mon Sep 21, 2009 5:21 am

There are some "Protek" digital scopes, both benchtop and USB, for a little under US $300.

You could get used Tek DSO on ebay for less, but you need to be careful what you buy and/or be lucky. From what I observed when buying a scope, the "good" ones went for $300 and up. My minimum specs were 100MHz or higher, digital scopes, without obvious issues. Broken switches, bad displays, failed self test were the common disqualifiers.

For Arduino stuff, audio, I2S interfaces, a 40MHz bandwidth scope will work. You could get by with as low as 10MHz. But check that the sample rate is at least twice the bandwidth. The bandwidth isn't very useful above 1/2 the sample rate.

Consider how you are going to use it. Will the students gather around the scope (then just about any type of scope will work, including analog)? Or do you need to project it (need a VGA output or USB scope)? Or do you need to capture the waveforms to put into handouts / tests (digital scope with USB or 3.5" floppy)?
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Re: Choosing a scope

by blalor on Mon Sep 28, 2009 3:17 pm

I bought a Link MSO-19 a couple of months ago and really like it. It's a USB oscilloscope and works very well on my MacBook and MacBook Pro running VMWare Fusion. I paid $250 for it. It's only a single channel and I've already wished I could have multiple channels, but I was really struggling trying to find a "real" o'scope in this price range that included probes and was guaranteed to work. The manual is utterly worthless and there's a BNC port labeled "out" that I haven't figured out what to do with, but I'm generally very happy with it.

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Please be positive and constructive with your questions and comments.