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Author Topic: Oscilloscope Needed?  (Read 1002 times)
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I am a newbie, so of course I want to jump in and buy one of everything at this point.  My question is: I have a chance to buy a used analog oscilloscope for $60.  My goal at this point is to build simple robots for fun.  Will the acquisition of such a tool be useful in my short/long term goals and understanding of basic electronics, or should I hold on to my money?

BTW- the scopes available are: Elenco S-1330 and the B&K Precision 2125A  Any preference if I were to buy? 

Thank you in advance.
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You don't NEED a scope.
These are 30 MHz scopes so you can use them to see signals from Arduino's lines.
But i'ts harder to find unwanted effects in those signals with these.
$ 60,- isn't a huge amount of money, for these (they both are offered for a lot more online) but could be put into some other stuff more useful to you.

I would get one of those if they look good and are fully functional, but already got the use of some scopes.

The nice thing about a scope regarding the understanding of electronics: a scope is a true way of visualising stuff that really is invisible.
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Have a look at "blink without delay".
Did you connect the grounds ?
Je kunt hier ook in het Nederlands terecht: http://arduino.cc/forum/index.php/board,77.0.html

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Personally, I think I would go with the B&K over the Elenco (B&K still lists the device with docs on their website), but both should be fine for starting out.

The real question is how you are getting one of them so cheap? Do they work? Have they been demonstrated to you? How well calibrated are they? What happens after they have been on for a while?

If they are used scopes, being sold by a "fellow hobbyist", hopefully that person can demonstrate them to you, and won't try to cheat you out of your money by selling you something that isn't fully working (for whatever reason). If you know what you are doing, you can test the basic calibration of the scope using it's built-in test signal (all scopes have such a signal; it's from a little pin that sticks out of the front, that you can hook one of the probes onto, then switch to that channel, and test to see if the signal is showing up properly, at the right voltage levels, and proper frequency across time-scales - try both channels, across all ranges and settings, as well as A+B, A-B, etc if you can hook two probes in).

Probably the best thing you can do first is download the docs for each scope, and read them; also find an online tutorial on how to use and read a scope, and study that, too. Then when you are fairly confident, ask the seller to demonstrate it, and check the test signal, etc. The test signal is generally a square wave of a set frequency, at about 5 volts peak-to-peak; it will generally say what it is right above the test signal hookup point on the front panel. If the output doesn't look right, don't buy it. You are looking for the general basics (proper readings on screen across all ranges and time-scales), as well as whether the rise and fall times are "crisp and clean" (edges need to be square - some rounding/ringing is to be expected, but only at certain scales and such), the display is bright, that there isn't any focus or skew/rotation issues on the display (see if you can adjust and maintain the focus/skew/display - there are little adjustment knobs set-back in the panel that you can use a small screwdriver to adjust; typically you use a non-metallic driver to do this, but if you don't have such a tool, a regular small screwdriver will work ok), etc.

The manual will detail how to do all of this and adjust the device properly; if you have to, print-out or otherwise take the manual with you to the seller's place and test it like that.

Ultimately, $60.00 isn't a bad price for such an analog scope, provided you know how to use and read it, and how to care for it. There are certain "gotchas" that you have to be careful with on just about all scopes (but most of the time they involve attempting to read a power signal from the same circuit the scope is plugged into - you need an isolation transformer to do this properly, otherwise you can bugger your scope), but for basic signal reading and use (and learning) - $60.00 seems like a great deal to me.

That said, just know you aren't getting any way to "store" a signal or do other similar analysis; analog scopes are mainly best use for signals that are repetitive or continuous in nature. Checking pulse trains, or audio signals, or RF signals and such - that's what these scopes are best at. If you need to analyze the rise and fall times of a digital signal train of data (like a serial communications channel or something), an analog scope won't work; you need a DSO (digital storage oscilloscope), or a logic analyzer.

In my opinion, it is best to start learning on a simple scope like you've mentioned; then you need to decide whether you want or need the other two tools. Sometimes, you can get a DSO that has a logic analyzer built in (be prepared to spend some real cash, though!); generally, though, you want your tools as separate as possible - so if you find yourself needing to analyze a set of data bus lines (or multiple digital signals in such a way that the correlate based on their timings), and that number of signals is greater than "2" - then a logic analyzer is what you'll want.

They do make oscilloscopes (DSO and analog scopes) that have more than 2 inputs; you can find ones that will have a "Z" input (this mainly controls the intensity of the gun on-screen - so you can use it for old-school TV repair, generally) - but there do exist ones with four or more actual inputs; sometimes, you can even find them used. But what I have seen, is that if you go beyond 2 inputs or 100 MHz of bandwidth, the cost for the scope skyrockets (add DSO into the mix - yikes! - at my work, all the techs have nice 4-channel Tek DSOs - not sure about the bandwidth - I so wish I could get one of those, just to have it - but likely, I would never need it - and honestly, I tend to wonder if they really need it, either, given my employer's business).

Note that a DSO and a logic analyzer are not interchangeable tools - usually. A DSO (or an analog scope) is designed not only to let you view and study the signal, frequency, and voltage of a signal - but it can also tell you whether there is any noise present on the signal itself, or in the case of digital and high-speed analog signals, "ringing" at the signal transitions (look it up). Generally, a logic analyzer will only show you for a given input whether the signal is HIGH or LOW in relation to the other inputs. There are logic analyzers, though, that can give you the finer-grain details about such digital signals (noise percentages, wave shaping, and ringing) - but you generally won't find such details on anything in normal human price ranges (it takes a ton of memory and a lot of speed to store such information for playback and analysis).

Finally - if you find yourself later wanting another used analog oscilloscope, the brands to look for are Tektronix and HP/Agilent - if they are in good condition and not too old (and have all their parts), a 2-channel 50-100 MHz scope will run about $200-300.00 USD. If you find one cheaper in good condition, snatch it up. I personally own a Tek 2213 - picked it up off Craigslist for $250.00, and it had been factory calibrated. I also managed to get an interesting 100 MHz Fluke Combiscope (PM3380B) fairly cheaply (I think I paid $350.00 for it a few years back). This is an old DSO, but what is really interesting about it is that it can be used in both "digital" and "analog" modes - you can even have a single trace recording into the DSO in "digital" mode, while the other trace runs in "analog" mode, so you can compare both analog and digital signals at the same time. It's really an interesting beast; you can't find such scopes any longer (all DSO's these days use LCD screens).

Ok - well - since someone else posted before me - I do want to second his/her opinion that you don't -need- a scope for most things in basic electronics (a multimeter is far more useful). All of his/her points are perfectly valid. But - at $60.00 bucks, provided it is in good shape and working well - that is a great investment for a learning tool. Don't expect to use it forever; you might find you don't ever need it - or you might find you can't live without it and want to upgrade to something better. Heck - even though I have the scopes I mentioned (and don't need to learn to use a scope), I would probably jump on that deal (it's like all the free Harbor Freight multimeters I get - I don't need them all, but they are handy now and then).

Consider it an investment in your education; worst case, after you have learned how to use it and whether you need it, if you find you don't need it as much, or want to upgrade - pass it on to the next newbie...
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My first impression as an Arduino/electronics newbie is that this is an amazing community!  Thank you for the responses; they definitely give me something to consider.  Take care.
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Maybe it's because the way I was raised and trained in electronics, and I'm an old fart, but I consider the basic O-scope the best overall general purpose piece of troubleshoot/learning equipment one can have. While a decent DMM is also a very basic requirement, a scope can let your see things that a meter just cannot show you.

 I presently have a Tek 2213 and use it a lot, especially on the analog side of the electronics world. So I guess it's what your educational goals are with using an arduino. Many certainly many if not most build, troubleshoot, and debug arduino projects without a scope, but if you want a tool that will help you in learning and advancing in the electronics world then a scope is a very worthwhile tool to get. And as your starting out a cheaper (assuming it's functional) used scope is a good path and you will learn in time what you actually need and want if you ever decide you need to upgrade to a more powerful scope (and expensive) with more features and functions.

Lefty
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On the topic of oscilloscopes for beginners, what do folks think about this type of item?
http://www.seeedstudio.com/depot/dso-quad-4-channel-digital-storage-oscilloscope-p-736.html
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I am with lefty on this. Electricity is invisible a scope is your eyes, it allows you to see.
Any scope is much much better than none.
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