Slashdot Log In
Cheap PC Oscilloscopes - Any Recommendations?
Posted by
Cliff
on Fri Feb 27, 2004 07:55 PM
from the waves-on-screen dept.
from the waves-on-screen dept.
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.
This discussion has been archived.
No new comments can be posted.
Cheap PC Oscilloscopes - Any Recommendations?
|
Log In/Create an Account
| Top
| 321 comments
(Spill at 50!) | Index Only
| Search Discussion
The Fine Print: The following comments are owned by whoever posted them. We are not responsible for them in any way.
Some places to check out... (Score:3, Informative)
(http://www.slashdot.org/~lukewarmfusion/journal/ | Last Journal: Tuesday August 02 2005, @02:49PM)
Here's one to check out -Price page is unreachable (Score:5, Informative)
(http://www.addictz.org/ | Last Journal: Monday April 18 2005, @04:00PM)
Re:Here's one to check out -Price page is unreacha (Score:5, Informative)
winamp? (Score:5, Funny)
(http://www.nickhart.com/)
Re:winamp? (Score:5, Insightful)
(http://www.lib.ru/)
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.)
Re:winamp? (Score:5, Interesting)
(http://www.seanadams.com/)
Re:winamp? (Score:5, Informative)
(http://www.npl.uiuc.edu/~fegray)
My understanding is that sound card inputs are AC coupled, so you won't be able to see anything much slower than about 20 Hz. That might be OK, but it's not quite an oscilloscope.
Re:winamp? (Score:5, Interesting)
(http://www.seanadams.com/)
Re:winamp? (Score:5, Interesting)
I agree with the parent post about a sound card being a nice classroom demonstration scope. For higher mhz, you can pick up a real scope from Ebay for much cheaper than a PC card solution.
AC coupling isn't a problem (Score:4, Informative)
With a simple analog multipler (for example, the Analog Devices AD834 [analog.com]) and e.g. a 5 KHz oscillator, you can AM a band-limited (say, DC-500 Hz) signal, put it in your sound card, then do the demod in software (another multiplication will work).
This will cost you, in total, about $5 (you can get free samples of the AD834 and you'll need some resistors, some caps, a couple op-amps, and some wire) and will give you DC-500Hz through your modulator or 20Hz-24KHz without it. Not too shabby, especially compared with $500.
By the way, if you're going to spend $500ish anyway, why not pick up a Tektronix 2445 or 2465 on EBay? The 2465 has 350MHz bandwidth and is, IMHO, one of the nicest all-around scopes out there.
Bankruptcy Auctions! (Score:5, Interesting)
(http://mobileoptimized.com/)
The only thing necessary for Micro$oft to triumph is for a few good programmers to do nothing". North County Computers [nccomp.com]
Re:Bankruptcy Auctions! (Score:5, Funny)
Re:Bankruptcy Auctions! (Score:4, Funny)
Sorry to go off-topic but since the question was about oscilloscopes I felt I had to add a logic probe!
Re:Try the sound inputs for a demo (Score:5, Informative)
That's not going to help you display DC and very low frequency signals. In fact, a soundcard's frequency response is un-linear enough that you really don't want to use one for demo purposes.
Like Skee Lo, I wish... (Score:5, Interesting)
(http://goat.cx/ | Last Journal: Wednesday August 18 2004, @02:34PM)
I also wish that teachers like yourself didn't have to worry about providing materials like this within such a tight budget. It doesn't sound like this is just for this year's class, but something that can be used year after year. $300 for a material that can be used multiple times seems very cheap, especially considering the intrinsic value of the tool. Schools should be at liberty to spend what is necessary to bring the classes up to exceptional levels. Considering how the U.S. lags behind most other modern Western nations in Math and Science, such tight-fisting seems to be one significant factor in this drop off.
Good luck in finding the right tool.
Re:Like Skee Lo, I wish... (Score:5, Insightful)
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.
Educational device (Score:5, Insightful)
- 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.
Re:Educational device (Score:5, Insightful)
I'm afraid this is one of the greatest misconception in the world education. It's definitely not cool when kids get to learn with the best equipment : kids should learn the basics on simple, self-explanatory equipment. Complication and better equipment can come later, when the basics are understood.
That's the same reason why, after universities have taught CS students Java, C++ and Visual Basic before C and assembler, and churned out unfinished computer "engineers" for years, us low-level programmers still get high-paying jobs doing the old non-object-oriented, boring un-cool engineering the right way.
Re:Educational device (Score:4, Funny)
(Last Journal: Friday March 21 2003, @03:46AM)
no no. Spit on Fosters, VB is drinkable.
Re:Educational device (Score:5, Informative)
(http://slashdot.org/ | Last Journal: Saturday February 15 2003, @02:04AM)
The other thing to consider is the input amplifier bandwidth (this applies both to analog and digital scopes). This is also known as slew rate. It describes how fast the input amp can follow a signal change. Imagine an ideal square wave with zero rise time. It has infinite bandwidth. What does this mean? If the signal has a faster riset time than your input amp, your edges will be smoothed out. If I look at the output of a 40 MHz TTL oscillator (which outputs a squarewave) with my 60 MHz scope, I see what is almost a sinewave. "60 MHz scope" means the scope can display a 60 MHz sinewave. The sinewave is the waveform with the slowest slew rate. All other 60 MHz waveforms will also look like a sinewave on this scope. If you want to analyze square waves, your scope will only show a halfway accurate depiction of the signal if it has upwards of ten times the bandwidth of the signal.
There are also problems when measuring high bandwidth signals. Above about 80 MHz, you need to use BNC jacks on both sides, properly terminated with 50 Ohms, or the stuff you see on your scope screen will have very little to do with the actual signal. Not many outputs can drive 50 Ohms. You need to build special prototypes of your stuff that are intended for scope measurements. You can't just take a scope to your CPU or stuff like that.
If I had to make a recommendation, get a 60-100 MHz analog scope in good condition. Tek 465 is a good model.
If you want to look at digital stuff, get a logic analyzer. There are some interesting DIY projects on the web.
For higher frequency or RF stuff, a spectrum analyser can't be beat. But good ones cost more than a luxury car. If you're really serious, there are DIY projects on the net for that, too.
Re:Educational device (Score:5, Informative)
(http://slashdot.org/ | Last Journal: Saturday February 15 2003, @02:04AM)
Re:Educational device (Score:5, Informative)
(http://www.macetech.com/ | Last Journal: Monday February 16 2004, @01:44PM)
If the poster really wants a digital oscilloscope, head on over to fpga4fun.com [fpga4fun.com]. There's some neat little FPGA projects, based on a little FPGA board the guy designed and is now selling for $50. One of the applications is a digital sampling oscilloscope; it actually looks pretty neat. With the FPGA board and ADC board, it's pretty cheap too.
Re:Educational device (Score:5, Funny)
(Last Journal: Thursday January 15 2004, @08:15AM)
3 times the highest frequency being measured (Score:5, Informative)
(http://www.futurepower.net/)
Remember that the oscilloscope bandwidth close to the frequency of the waveform being measured distorts that waveform. (In phase if the frequency being measured is a sine wave.) You need an oscilloscope bandwidth maybe 3 times the highest frequency being measured.
ICs often have very high potential bandwidths, and, when something goes wrong, even an audio IC can have sometimes have parasitic oscillations at extremely high frequencies. If you are working on a circuit, you need to be able to see those parasitic signals.
I don't like this fact, because it is expensive, but 100 MHz seems to be a good oscilloscope bandwidth. I bought a very old Tektronix scope to get the needed bandwidth at a reasonable price.
Re:3 times the highest frequency being measured (Score:5, Informative)
see the tektronix documentation, for ex. 2x is the standard shannon-nyquist theory, but to get proper results, go 5x. tek has a huge document on it, quite informative.
Re:3 times the highest frequency being measured (Score:5, Informative)
Imagine a sine wave.
If you do 2 samples/period, you measure at 0 and 180 degrees and you get a flat line.
If you do 4 samples/period, you measure at 0, 90, 270 and 360 - resulting in triangular waves.
If you do 6 samples/period, you measure at 0, 60, 120, 180, 240, 300, 360 - the result is more like a sine wave, still the amplitude is about 30% off.
If you do 10 samples/period, the result finally resembles the original (to a certain degree).
Who the fuck modded this Informative?
This is flat out wrong.
The sampling theorem is, strictly:
If a continuous function only contains frequencies within a bandwidth B, it is completely determined by its value at a series of points spaced less than 1/(2B) seconds apart.
This means that with anything greater than 2 samples you can theoretically reconstruct the continuous bandwidth limited signal. So, your first example is somewhat right, and is why we say "less than 1/(2B)" rather than "less than or equal to" This means 2.1 samples/period or even 2.00001 samples/period is enough.
You are making a common misconception that the reconstruction of sampled signals is done by plotting points and connecting the dots with a line. This is not the ideal way. Ideal reconstruction looks something like this:
Sigma(i=0, K, x_i*sinc(pi*(t-t_i)/dt)). Of course this is not a practical reconstruction in real time applications because of the need for "future" data, but with it you can mathematically prove to yourself that one can reconstruct perfectly with any sampling rate greater than twice the maximum frequency.
You should read up on signal processing.
The OP was talking about bandwidths as it applies to practical devices which involves stuff having to do with clock jitter and SNR (oversampling can be used to increase effective SNR).
Re:3 times the highest frequency being measured (Score:4, Informative)
If a continuous function only contains frequencies within a bandwidth B, it is completely determined by its value at a series of points spaced less than 1/(2B) seconds apart.
The key assumption is that the frequencies contained by a signal are indeed limited to a bandwidth B. For example, an NMR Free Induction Decay signal may have a linewidth of 1 kHz, but if you try to use a 1 kHz filter on the signal, it is going to look very distorted (even with a gaussian or bessel filter). The key issue here is that while the decay may have a bandwidth of 1 kHz, the initial rise may have a 50 kHz bandwidth.
Basically any time you want to maintain reasonable time domain response, you need to use either a gaussian or bessel filter. Neither of these filters has a particularly rapid roll-off and it ends up that a sample rate of 10X of the bandwidth is useful to minimize aliasing.
Re:3 times the highest frequency being measured (Score:5, Informative)
(http://www.sjbaker.org/)
You are concerned about reconstructing the details of the shape of the waveform - but that's not at issue here. We're only promising that if you look at a fourier transform of your signal - then the highest component of that that we'll reconstruct must be less than half of our sampling frequency.
When we are way up there where we have only two-and-a-bit samples, the only shape we can possibly see is a sine wave because anything else would have higher frequency components - and then we are off the hook - we don't have to reproduce those kinds of waves accurately.
So - the issue is whether you can deduce the phase, amplitude and frequency of a sine wave from just two-and-a-bit samples. Nyquist says you can - and he's right.
Stop thinking about how you'd draw graphics of a sinewave using only three numbers - this is signal processing - not graph plotting.
If you want to see a 40MHz square wave, you may well need a 400MHz scope - but for a 40MHz sine wave, a 40MHz scope (which samples at a little over 80Msamples/sec) should be plenty.
Everything oscillates. Okay, a small exaggeration. (Score:5, Informative)
(http://www.futurepower.net/)
Modern circuits are not so well controlled as someone might guess. To have 20 kHz output with little phase distortion, it is necessary to pass more than 200 kHz.
But that's not the issue. ICs allow the design of circuits with bandwidths that are literally physically impossible with discrete components. The fundamental bandwidth limitations of the transistors used in the IC may be 200 MHz or more, or even 1.5 gigahertz. Any small problem can cause a circuit to oscillate at 50 MHz, even if the IC is supposedly limited to far less than this.
All you need for oscillation is gain and some positive feedback. In the real world, circuits try all possible combinations almost instantaneously, and begin oscillating for reasons the designer never foresaw. For example, maybe there is capacitive coupling through the IC packaging, and the output circuit alone is oscillating.
This is only a slight exaggeration: There are 4 steps toward making a new electronic device: 1) Build the circuit. 2) Supply power for the first time. 3) Apply an oscilloscope probe and begin discovering all the reasons the circuit is oscillating when it shouldn't. 4) Then discover all the other reasons the circuit isn't working correctly, if any.
I was never a person who thought that killing people and destroying their property was a good way to resolve social problems, but at one time it was my job to repair the automatic flight control systems of fighter-interceptors in the U.S. Air Force's Air Defense Command.
These aircraft required 250 hours of maintenance per hour of flight. (Aircraft meant to be sold to other nations, also, required 15 hours of maintenance per hour of flight. I've followed the development of weapons systems ever since, and my opinion of what is actually delivered is that it is often fraud, or close to fraud. United States taxpayers: Your assigned duty is to find the money to pay, and to avoid thinking.)
Anyhow, during training flights it was required to pull several g's. Sometimes at high accelerations the electronics would go completely crazy, and all inertial reference would be lost. The only fix for this at the time was to land, regain stability, and take off again. The aircraft that had this problem were therefore not much use for any situation actually requiring defense. Worse, the problem seemed to have nothing to do with any particular aircraft, but seemed random.
One day while trying to make a faulty system work on my bench test mockup, I discovered the reason. Some of the amplifiers that controlled the gyros had high frequency parasitic oscillations at perhaps 100 times the normal frequency of operation. You couldn't see the oscillations with normal equipment because the frequency was too high. I had borrowed an oscilloscope from some co-workers who worked on faster electronics.
The design of the amplifiers was acceptable, but many of the amplifiers had bad solder joints. Those with bad solder joints would oscillate; oscillating amplifiers would amplify at the required low frequency, but had a much smaller dynamic range than amplifiers that were not oscillating. (Yes, that bad solder joints could cause this doesn't make much logical sense, but most parasitic oscillations don't make much logical sense.)
The amplifiers had other defects that caused them to have a high failure rate. Every time an amplifier was pulled from an aircraft for a conventional repair, an amplifier was drawn from stock and put in the waiting aircraft so that the aircraft would be immediately operational. That was the reason the instability problems kept moving from aircraft to aircraft.
I drew a circuit diagram of my test setup, wrote an article about the problem, had a photographer take photos of the test setup, took screen photos of the parasitic oscillations, and sent everything to those who review such things. This had several effects. Someone at Air Defense Command headquarters wrote a letter praising my work. When everyone was reviewed for p
Educator? (Score:5, Informative)
(Last Journal: Thursday December 04 2003, @09:30PM)
*Here is a link to Agilent's educator page complete with educational discounts etc.
http://www.educatorscorner.com/index.cgi?CONTENT_
*Write to sales reps at different companies, Tektronix, Agilent, etc... and plead for donations.
*Write/apply for a grant for add'l $$ (after all, you get what you pay for in regards to scopes)
*If all else fails, peruse *cough* ebay, or *cough* broken windows at ___ Electonics Supply... [grin]
Re:Educator? (Score:5, Interesting)
Not PC (Score:5, Informative)
A friend of mine bought a couple at a ham radio swap meet from a guy who buys surplus lots. IIRC they were dual-trace and something like 20MHz (he ended up getting one for me and for several other interested friends).
They were selling for ~$20 which means you could have a scope for every student in a class of 20 and still stay in your budget.
Must it be PC-based? (Score:5, Informative)
(http://www.swampgas.com/)
I also have an Ozi-Fox handheld that has a PC and/or palm-based interface. It only does 20mhz and is single trace, but they are fairly inexpensive (< $90.00 USD) -- you could buy multiple units for classroom use. The display on the unit itself is not great, but works well for quick-and-dirty work.
Good luck -- m
How bad are "soundcard" o-scopes? (Score:4, Interesting)
(Last Journal: Saturday December 09 2006, @10:46PM)
After all, a DSO is "just" a D/A, and the input of sound cards is the same.
Maybe the sample rate on sound cards is not high enough, but the specs on some of the latest SoundBlaster (creative labs) cards are impressive (106dB...).
If you really need a good scope, you'll likely have to spend money. But if you are a hobbiest who just needs to see basic waveforms, maybe there is some good, cheap software out there that takes advantage of commodity soundcard hardware?
Why PC tethered? (Score:5, Informative)
(http://www.demaagd.com/ | Last Journal: Sunday October 27 2002, @06:53PM)
I'd just find a real scope on surplus somewhere.
I just have a 'scope on "loan" from a local EE guy. Just an analog one. Effectively it is mostly a gift, but there are times he wants an analog scope so he wanted the understanding that he can get it back on occasion. For most uses, a digital one does fine.
Did you look all that hard? (Score:5, Informative)
(http://anti-slash.org/)
It is not difficult to find a veritable mount of cheap oscilloscopes [ebay.com] on eBay. You say you only need it for demonstration purposes, so why do you need something shiny and new? It can even be argued that the older analog oscilloscopes are better than newer digital ones. As always, resort to eBay if you need something not so good, and fairly cheap. Chances are you can find it there.
Audio Frequency Freebie (Score:5, Informative)
Its slow, but is free (assuming you have the sound card).
Re:MHz vs. MSPS (Score:5, Informative)
(Last Journal: Saturday June 30, @01:22AM)
Most digital scopes do a sort of interpolation when the frequency is above Nyquist, they will sample the signal for several periods and reconstruct what the waveform looks like, this works with any repeating signal, but when you use this you can't catch transient events, for that you do need a sampling rate several times the base frequency.
Re:MHz vs. MSPS (Score:4, Informative)
You need 2x samples to capture a waveform. Mathematically. However, we are in the real world, and 5x is considered generally adequate. Truthfully, most engineers won't let a 40MHz scope anywhere near a 40MHz signal; equipment doesn't tend to perform optimally at its edges.
As to why buy a digiscope for repeating signals: data capture is nice. Especially when you can capture raw sample values and spit them into MATLAB to do some serious data analysis. Also, there's the fact that you can't buy new analog scopes anymore. Finally: most DSOs will also function as a spectrum analyzer. Which is great on your repeating signals.
Windoze luzers with Tektronix 2400-series DSOs.... (Score:5, Informative)
(http://www.ke5fx.com/ | Last Journal: Tuesday May 20 2003, @02:09PM)
I use a Tek 2430A on my own bench. These are great scopes -- you can get 150 MHz bandwidth for about $400-$600. A National Instruments GPIB adapter to interface it to the PC will set you back another $100.
I'm trying to add support for as many instruments as I can to this package. Any interested parties should feel free to email me...
Try the USRP (Score:5, Informative)
Re:Try the USRP (Score:5, Informative)
(http://slashdot.org/)
Bitscope (Score:5, Informative)
(Last Journal: Saturday June 30, @01:22AM)
Visit #electronics (our electronics+open source channel) on irc.freenode.net if you want to discuss.
nyquist frequency (Score:5, Informative)
The bitscope only has a 40MS/s data aquisition rate. Assuming that that's for both channels - 20MS/s each, then your left with a nyquist of 10Mhz. And you really need to oversample a waveform a lot more than x2 to see what it looks like. The analog bandwidth of the bitscope is high, but the A/D conversion will result in a lot of aliasing. That said. Its a really impressive unit for $400.00. I didn't think you could find something nearly that fast for under $700. Not exactly what you're looking for.
The software for a scope is pretty important - but without the raw A/D speed and resolution you won't get very far.
Try DRMO for some HPIB/GPIB compatible gear (Score:5, Informative)
(http://veraperez.com/ | Last Journal: Thursday January 12 2006, @11:14PM)
This is the military agency that sells surplus equipment to the public. They usually have stuff like what you need.
If you can find something that has a HPIB/GPIB bus connector (IEEE-488) then you can connect it to a PC and use program your own interface (the libraries are very simple and very well documented). We did this both in the Army and also at a commercial satellite communications company (ours was to interface with HP spectrum analyzers thru IEEE-488).
SoftDSP Digital Oscilliscope (Score:5, Informative)
(http://www.esmonde-white.com/)
I bought one two years ago (around 800$ canadian)
it's pretty good, does 200 MHz / (5 GigaSamplesPerSecond equiv., whatever that means), two channel, USB.
The software isn't great. I don't think there is a linux port... I'm lazy, haven't checked recently.
The actual device is really sweet. If I haven't blown it up in two years, it is pretty solid! (I'm a chemist, and I do things like attach 400V power supplies to it randomly, I'll feel bad if it dies. Or me.)
Good luck!
Labview (Score:3, Informative)
http://www.ni.com/academic/edu_dsct.htm
(you should double check that the educational version actually supports GPIB because I don't recall if it does).
There's a hell of a lot of corporations out there that use LabView for all their test equipment, so there's a good chance your students will run into it when they get jobs.
PCI based oscope (Score:5, Informative)
(http://www.dimlight.org/number9)
a PCI card... but the ones I have used were GaGe...
http://www.gage-applied.com/
Should not be too pricey, and I think they have
educational discounts. They are the best option
I have seen to get a real oscope in a computer, and
the sampling rate and digitization will beat a sound card hands down.
Take a trip down to your local electronics swap... (Score:4, Informative)
Personally taking a trip down to your local electronics swap meet is not a bad idea if you have one nearby. Hear in SiValley there are a few around on the weekends where you get some older Tek/HP *cough* Agilent scopes for pennies on the dollar. Sometimes they need some work but most people are honest about it.
-Ho
One to Avoid (Score:5, Informative)
(http://www.certsoft.com/)
I bought a DSO-2100 from Link Instruments and have been very pleased with it. Probably one of the best investments I've ever made.
Optascope (Score:5, Informative)
http://www.optascope.com
I recommend it highly. Nice software and really works well for me. Also only $189.00!
Specs are:
1 Ms/S Maximum Sample Rate (500Ks/s 2 channels)
200 KHz Bandwidth
20Vpp Max Input for CH1 & CH2
8 Bit Vertical Resolution
2 Channel
External Trigger Source
Trigger on Rising or Falling Edge at Any Voltage
Variable Trigger Voltage on DSO channels
10%, 50% and 90% Horizontal Trigger Position
Auto or Normal trigger modes
USB interface
Dupe! (Score:5, Informative)
-----
Trogdor the Burninator!
Why not a real oscilloscope? (Score:3, Informative)
There are a quite a few used Tektronix 465 scopes going for about $200. Check newsgroups, eBay and go to some Hamfests.
cheap 40 MHz scope (Score:5, Informative)
(http://w2ww.slashdot.org/)
If you are teaching about electronics, you would be better off buying a used Tek 475 (or similar) analog scope, you can get a very good one for $300-400. They can learn about the actual circutry, timing, measurement error, etc. without
getting heavily into sampling theory and digitial
signal processing.
If you want the students to learn "the new way" of
electronic instruments, check with National Instruments about used/traded in cards, and software; they may have an educational discount.
There are also some "poor man's" type of scopes made of surplus parts, old TV's, etc.. that you can find in the back pages of Nuts& volts magazine; I don't recommend these if you want the students to learn what they will use in the future, in real-world engineering applications.
Finally, there are mixed-mode instruments that are analog with analog storage, analog with digital storage, analog with digital readouts added, various standard instruments with serial or GPIB interfaces, and s/w from the mfr or 3d party for
control and analysis.
See if you can find on some engineer's shelf a catalog/book from Tek or HP, say, from the 1980s
or 90's, this is about the vintage that will work and be in your price range.
Have you considered eBay? (Score:3, Interesting)
Check out National Instruments (Score:3, Informative)
Check out Interface's Boards (Score:3, Informative)
(http://slashdot.org/)
I've done some preliminary work on writing signal-analyzer software for their PCI-3525 board, which I would be happy to share (it's not close to being fully-functional yet, but we've got a student who may be using these boards, so that might change soon). I'm also happy to try to adapt this code to more general use. With these boards and existing code, your task might be much easier than you originally thought. Also, their sales engineers are very willing to help solve problems. I don't know the prices on their boards (ours were donated), but they are excellent devices.
Another use for that old gameboy (Score:3, Interesting)
(http://www.babatatas.com/)
Please... Don't go the PC route for this... (Score:5, Insightful)
(http://www.bluefeathertech.com/ | Last Journal: Friday November 04 2005, @11:51AM)
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.
Re:Here's a good one (Score:4, Informative)
(http://www.2005dauphin.org/)
Was that supposed to be funny?
Re:Here's a good one (Score:4, Insightful)
Re:Here's a good one (Score:5, Interesting)
(http://www.ke5fx.com/ | Last Journal: Tuesday May 20 2003, @02:09PM)
Not a bad solution, all in all, at least until you hook up an Ethernet cable to transfer some plots and your $20,000 scope gets r00tz0red and drafted into service in the war against SCO.com.
Re:Here's a good one (Score:5, Funny)
(http://slashdot.org/)
Re:Here's a good one (Score:4, Interesting)
Re:Cheap PC Oscilloscopes (Score:5, Funny)
(http://slashdot.org/ | Last Journal: Tuesday February 24 2004, @04:37AM)
If you google for "Cheap PC Oscilloscopes" with the quote marks included all you get is a link to this article.