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Basic Electronics » This a decent oscilloscope?

June 23, 2010
by Phrank916
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I'm asking because I really trust the collective opinion of this forum, but this seems like a pretty good deal:

http://sacramento.craigslist.org/ele/1799244495.html

It does have a minor problem that is listed in the ad:

Small Problem: On Channel A, the variable amplitude control knob is broken. 
The signal cannot be adjusted to the variable settings. 
So the input it set to full amplitude. The trace works fine otherwise.

What do y'all think? Worth it?

Ted

June 23, 2010
by mongo
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For $100.00, you bet.

June 24, 2010
by BobaMosfet
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Phrank916--

Hold on-- Even at $100, it is NOT a good deal if it won't actually perform the way you need. Even at $100, particularly in this economy, this is a serious investment, and you definitely do not want to wind up with something sitting collection dust most or all of the time.

There are things you need to understand (None of which are necessarily obvious) prior to getting an o-scope.

  1. The o-scope should be at least 5 times FASTER than the fastest signal you plan to look at. This is directly related to how many times the oscilloscope can sample the input voltage per time-interval. In the case of this scope, 100Mhz, means that the fastest signal it can realistically be used on, is 20MHz. If you never do anything beyond what the ATMEGA168 can do clockwise-- perhaps this is fine. But if you intend to get more use out of the unit-- you need to take your time and look around. But if you want to use it on some higher frequency-- at very fine resolution, this o-scope cannot sample the input signal fast enough to show you the entire wave-form accurately. I would recommend, if you intend to do this seriously, to not settle for less than a 200Mhz scope, preferably a DSO.

  2. Big red flag (unless you have a source)-- no probes. As important as the oscilloscope is-- it's just a fancy voltmeter that can show you voltage change over time-- the most critical part of the entire thing is the probes. I kid you not. The probes come between the scope and the circuit. Because they are so critical, a single good probe could potentially cost you $200.00. Sure, you an get probes in all kinds of places for less, for a variety of scopes, but you also want accuracy-- a probe that does not 'load' or impact the circuit you're looking at (which would result in a change of the voltage level being reported). My point being this-- you don't want to have to pay another $400 for two good probes, when you might (for say, $350)a better o-scope and a couple of probes.

  3. Broken adjustment knob-- is the knob broken, or its ability to adjust? How much would it cost to get that fixed? I mean... the knob is there for a reason, and you don't want the scope to become a hassle because you can't view a signal properly because you can't adjust the output.

Don't get me wrong. I think $100 is a very good deal for an o-scope. You just want to make sure that you don't buy a problem. As for brand, I say tektronix. They are, and always have been the leader. Many, many tektronix scopes are out there on the market for a very reasonable price, that will do you better (IMHO).

Just keep in mind, your o-scope should be able to accurately report voltage levels that your voltmeter cannot.

Just my $0.02, so now you have an alternate view :D

BM

June 24, 2010
by mongo
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Good points Boba...

My response was to the thought that for a C-note, it ain't a bad price considering what they sell for new. I have had my share of bad scopes in the past but when you don't have one and need one... well There ye go.

The little Nano scope I bought a while back is all I have at the moment and in spite of the built-in short comings, it does what I need and is pretty darned accurate too. I would much prefer a 4 channel Tektronix storage scope but that is a bit out of the budget.

There are always work-arounds if needed.

June 24, 2010
by Phrank916
Phrank916's Avatar

Thank very much Mongo, and also to Boba: Your insight and expertise on the subject is appreciated. I've also read other info from Boba regarding oscilloscopes whithin other threads in this forum, and it's all very helpful.

I've decided to hold off on an oscilloscope purchase and do a bunch more research before jumping into anything. Thanks again for taking the time to give me "shopping" advice, hehe!

Ted

June 25, 2010
by BobaMosfet
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mongo--

I agree entirely-- my big red flag was no probes. Depending on a person's need, that can get spendy.

BM

July 30, 2010
by endrien
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You can get a pretty good new scope for 372$ http://www.dealextreme.com/details.dx/sku.30573

December 14, 2010
by danuke
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Well, I am not sure, I was just glancing at stuff, but I think that the MCU output 20MHz. If so, that looks like one needs a 100MHz scope minimum. Someone needs to verify this however. I do know that this is the range of of any scope that I will buy one day in the future, higher if I can afford it, seeing as how that is really the ultimate ee tool for today's tinkerer, in my opinion.

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