has anyone used the cheap 2 Channel PC Computer Digital USB Oscilloscope on ebay

[steveeeee]

hi, i'm looking for a dirt cheap scope and you see these all over ebay

http://www.ebay.com.au/itm/ws/eBayISAPI.dll?ViewItem&item=110833685985&ssPageName=ADME:X:RTQ:AU:1123

has anyone used one? what do you think?

i'm building an LED light cube, all TTL logic level stuff, not super fast, so i don't need cutting edge.

thanks

 

[(*steve*)]

They are only 8000 samples per second. That's woefully slow.

You'd be better odd with a DSO Nano (even though it's only a single channel)

 

[steveeeee]

They are only 8000 samples per second. That's woefully slow.

You'd be better odd with a DSO Nano (even though it's only a single channel)

that worries me two but i think i can slow the clock way down on my microcontroller so the scope can keep up. i'm worried that 1 channel is not enough.

i can also look around for a 2nd hand real scope but that will be easily 5x the price i think. maybe the better choice in the long run through.

 

[davenn]

that worries me two but i think i can slow the clock way down on my microcontroller so the scope can keep up. i'm worried that 1 channel is not enough.

i can also look around for a 2nd hand real scope but that will be easily 5x the price i think. maybe the better choice in the long run through.

Thats not really the problem

with such a slow samples / sec it means that the bandwidth ... that is the frequency range of the scope is really low.
Now personally I dont know how to convert 8000 samples a sec to bandwidth but you may find that only equates to say a 1MHz scope, which means its really only good for low freq audio signals

Now I hear this comment bandied around on various forums, that to avoid what is called anti-alising problems, that the analog to digital converter needs to sample at at least twice the freq being observed.
Now if I havent got that wrong and some one, I'm sure will correct me, that would mean that the max freq you would be able to observe without problems would be ~ 4 kHz. The middle of your audio range.

Dave

 

[steveeeee]

Thats not really the problem

with such a slow samples / sec it means that the bandwidth ... that is the frequency range of the scope is really low.
Now personally I dont know how to convert 8000 samples a sec to bandwidth but you may find that only equates to say a 1MHz scope, which means its really only good for low freq audio signals

Now I hear this comment bandied around on various forums, that to avoid what is called anti-alising problems, that the analog to digital converter needs to sample at at least twice the freq being observed.
Now if I havent got that wrong and some one, I'm sure will correct me, that would mean that the max freq you would be able to observe without problems would be ~ 4 kHz. The middle of your audio range.

Dave

yep, that's called the nyquist frequency. i guess this scope isn't useful for much at all. i'll just have to dig in my pockets and buy a second hand one. at least i can sell it on later if i don't have any follow on projects (i'm more of a software guy really)

 

[(*steve*)]

Now personally I dont know how to convert 8000 samples a sec to bandwidth

They claim 3 kHz.

Mr Nyquist says 4kHz.

If you want about 10 points per cycle (so you can see a *very* rough shape of a waveform, it's 800Hz.

Calling it "poor" would be to overstate it's capabilities.

Effectively it's just a very poor audio input device. And by "Very Poor", I mean it's not even as good as a USB audio device.

 

[davenn]

There's a whole bunch of us that deal with these things with our digital seismograph systems ( earthquake recorders) my own system has a 16bit A to D converter
I usually run at 100 sps which is quite low even in comparison to the scope system mentioned above.
But we are only really interested in freq's up to ~ 10 Hz at the most and anything above that is mainly manmade noise which we filter out anyway.
most of the signals from the big distant events are in the range of 0.001 to 1 Hz, ie. 100 sec / cycle up to 1 cycle / sec. my current seismometer has a natural period of 11 seconds.

after that little diversion on sampling ....

Steveeeeeee, decent used scopes up to 50 or 100MHz are readily available for under US$500. and a Tektronix in that range would likely to last you years. If you have ~ $800 to 1000 to spend then you could look at some of the other modern digital scopes available that are very compact with their LCD screens and lots of features

cheers
Dave

 

[steveeeee]

thanks, i live in Thailand and second hand stuff is hard to find here but i've found a few places that resell older equipment from the electronics assembly places, so i think i'm ok

 

[selanac]

I've seen equipment being sold in Storage Lockers. They have a t.v. show in the US called Storage Wars. Every now and then I see an Oscope in one. Then they auction off the whole locker.

You can probably contact the buyers. They always have t-shirts, and vehicles with the company names and numbers.