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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.
Check this one out. . . I don't know the price because their price page is broken. . . It looks like everything you need in a PC Oscillioscope.
YOU'RE WINNER !
Another lame blog
I think my media player has an oscilloscope...
--Nick
Search google for bankruptcy auctions. I'm sure you can find what you're looking for. I work for a biotech that saved 75% of our initial budget by acquiring medical laboratory supplies from six other biotechs that went bankrupt in recent months. We did such a good job, our VC company gave us more than we asked for to buy the rest of what we needed.
The only thing necessary for Micro$oft to triumph is for a few good programmers to do nothing". North County Computers
I sometimes think back to my college days and really regret that I didn't focus more on the hardware side of computer engineering, primarily delving into the Computer Science land of algorithms and language design. In the last several years of my employment in the embedded space, I have come into contact with more hardware than you could shake a stick at, and without that grounding in hardware that I should have gotten in school I feel a little overwhelmed when faced with anything deeper than a block diagram.
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.
I have been pwned because my
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
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.
For cheap demo purposes, consider using the analog sound ports (line-in). I have had good success doing that for lower speed (44.1K).
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.
"A door is what a dog is perpetually on the wrong side of" - Ogden Nash
Comment removed based on user account deletion
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
Roving Web-Teleoperated Robot
It seems people on slashdot are a bit overeager to buy PC based devices that can't be used as a standalone device. So far that I've seen, the benefits are mostly just cost, at the expense of portability, usability and quality.
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.
It is not difficult to find a veritable mount of cheap oscilloscopes 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.
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If a 2 channel audio frequency scope is all you need, then Oscilloscope 2.5 for Windows might do the trick. It uses the inputs on a standard sound card to grab 2 channels at up to 20 kHz. Disclaimer: I've not used it and a bit of Googling may find better alternatives.
Its slow, but is free (assuming you have the sound card).
Two wrongs don't make a right, but three lefts do.
If my understand is correct, some of the guys from the GNU Radio Project have developed a USB based software radio device that works with in linux. It is called the Universal Software Radio Peripheral. I think the first prototypes have shipped. The cost is pretty close to your price range. You can see it in action running an oscope program here. And of course it can be extended to do many more exciting things.
Since no one who's replied has answered your question, instead choosing to talk about unrelated things, I have to say that I'd go with the Bitscope.
Visit #electronics (our electronics+open source channel) on irc.freenode.net if you want to discuss.
I've had enough abrasive sigs. Kittens are cute and fuzzy.
Ya left one out. Write/go to any local company doing e-tech type manufacturing or engineering. Ask if they'll donate their old obsolete eqpt that they've already written off. I've never been in an engineering lab yet that didn't have at least one dinosaur in it.
Cloned foods give the statement "We had that last week!" a whole new meaning.
You don't need 10x samples for most things. You need around 5x to catch most transient events. You only need 2x to make a waveform per Nyquist.
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.
I've had enough abrasive sigs. Kittens are cute and fuzzy.
softdsp.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!
Many people make them, and they are real oscopes on
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.
I have an Optascope 81M USB scope from
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
This was covered a few years ago; no surprise that most people forgot. The answers are mostly the same; still a good read though: http://ask.slashdot.org/article.pl?sid=01/12/07/19 1220&mode=thread
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Trogdor the Burninator!
The most common source for these type of PC-card "instruments" is National Instruments.
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.
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
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