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Cheap PC Oscilloscopes - Any Recommendations?
Missionary Man asks: "I'm an electronics teacher looking for a good (but reasonably cheap) PC based oscilloscope for classroom demonstration purposes. I've done a reasonable amount of research and come up with a few contenders. Ideally I'd like something with a bandwidth of up to 40MHz and 2 channels. Does anyone have any tales to tell regarding the use of any of these scopes (or any others I haven't found or mentioned) and can recommend a suitable device?"
"Here's the list of my findings so far:
- The DS2200C from USB Instruments will do 2 channels at 12 bit resolution, but only to 200KHz.
- The PCS100 from Velleman at QKits runs to 12MHz, but only 1 channel. It has a bigger brother, the PCS500, that has 2 channels and 50MHz bandwidth, but is a lot more expensive.
- Picotech do cheaper ones, like the ADC-40/42, but these only operate in the KHz ranges.
- Link Instruments sell the DSO-2102S that runs to 60MHz with 2 channels, but it's a bit out of my price range.
- Finally, I found the bitscope which seems to be just what I'm looking for, combining a 2 channel scope and an 8 channel logic analyzer for a reasonable price.
Two thoughts about your question:
- Do you really need 40MHz for educational purposes? Unless this is a device to be used in a college or higher education class , you can display sub-10KHz signals to teach a class how to use a scope.
- When I was at school, I learned how to use a real scope, with knobs and buttons and a not-so-perfect green screen, and I reckon it was way better to touch these dials and controls and have a direct feel for what they did on the screen than set some virtual thing and grab perfect-looking samples, to understand how things actually worked.
In short, any old regular scope that's well explained by the teacher is probably better than any interface+software setup that "isolate" the student from whatever electrical phenomenon he's trying to expose.
"A door is what a dog is perpetually on the wrong side of" - Ogden Nash
This is not an informative comment - the budget is between $300-$400, and the oscilloscope linked is $21,500 list price - I doubt the used price would be within the budget. Mods, let me remind you that moderation is not a race. Follow the link and pay attention before you assume it's informative. I'll gladly take the karma hit for this if the mods resposnible for this can wake up.
I was thinking that one advantage of a PC scope is that you could project it. It would be neat to project that, and then next to it project an enlarged view of what you're doing, say probing a PC board. I don't know if this person is doing this or not but it's certainly one option to consider. Projectors are getting cheaper all the time, they're pretty readily available now.
"You're right," Fisheye says. "I should have set it on 'whip' or 'chop.'"
Back in the day, with even the highest quality most expensive analog scopes, you didn't trust any measurements off them before at least a twenty minute warmup.
Boy, have things gotten twitchy in tech these days, if a 30 second startup isn't fast enough. Nintendo has spoiled a whole generation.
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A good PC-based device allows storing the waveform. This makes documentation much easier. Scope cameras are a nuisance and using them a lot runs into significant film costs. Standalone digital oscilloscopes with storage capabilities are less convenient and not cheap.
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What you are doing is basically undersampling the incoming signal and then assuming that the original falls into one of many aliases that the undersampling generated.
In other words, if the signal changes while you are sampling and reconstructing it, the change is lost and results in incorrect reconstruction.
The original poster's question assumes that the PC-based scope is the best solution to his problem. My EE experience tells me that generally you want a standalone scope (you want as many screens as you can get, space be damned.) Teacher's needs, of course, may benefit from the PC-based scope (multicasting the readings to students' computers, for one.)
Sounds to me like the question is from a high school teacher. I seriously doubt spending any more on a scope would be worthwhile, since I'd bet it's primarily going to be used to show students wavy lines, or maybe as a glorified multimeter (he's only buying one, so it's not like the students will be using it regularly). I wish the poster gave a few examples of the types of projects his class works on.
That said, I wish schools would stop blowing their entire budgets on computer labs. I hate to see a school paying for a computer that isn't at least two years old when the money could be going to text books that aren't twenty years old and falling apart.
It would be really nice to see high school electronics courses teaching students how to properly work a scope, but you'd need enough for an entire class. It's amazing how many engineering students get 2 years into a computer/electrical engineering program and don't know how to use a scope to read important parameters from a circuit.
For the amount of money you're specifying, you can easily pick up a much better built and far more versatile O-scope in the form of an older Tektronix instrument.
In fact, that price range will easily get you a 475 or 475A, good to 200 or 250MHz, respectively. It will also put you well within reach of a nice Tektronix 7000 series benchtop 'scope, like a 7704 or even a 7904.
No matter what you may hear, the PC was never designed to be an O-scope, and no amount of external hardware, I believe, will ever turn it into anything that can compare, in terms of value for the $$ and quality of construction, with early Tektronix hardware.
I believe it's also EXTREMELY important to teach would-be technicians and engineers that the PC is not the be-all and end-all of test gear. Never has been, never will be. Oh, it can be useful as an instrument CONTROLLER in automated test setups, yes, but it was never intended to replace the functionality of actual made-for-purpose test equipment.
Give your students a real education. Get a real oscilloscope.
Bruce Lane, KC7GR,
Blue Feather Technologies
...and the old PCIIa GPIB-interface cards for the PC (they have a 8bit ISA bus!) are supported by linux-gpib since not long ago!
http://linux-gpib.sourceforge.net/
They are no longer supported by national instruments since windows 3.11/DOS, so you can get them very cheap (or for free) and they work very well under linux!
"By the way, if you're going to spend $500ish anyway, why not pick up a Tektronix 2445 or 2465 on EBay? The 2465 has 350MHz bandwidth and is, IMHO, one of the nicest all-around scopes out there." This is the best idea of the lot. In real life they will use a stand alone scope 90% of the time. The instruments on eBay are dirt cheap! When the break - and they will - trash them. Any of the 2000 series from Tek will do the job. The added benefit is that you get a REAL instrument not just a simulation or another piece of software that clogs up your DOS machines.