USB Oscilloscopes

[thinman]

Does anyone have any experience of these cheap USB oscilloscopes? Are they OK for basic audio frequency diagnosis?

[url="http://www.virtualvillage.co.uk/2-channel-5v-pc-usb-digital-storage-oscilloscope-new-001482-009.html"]Example item[/url]

[BanditSid]

[quote name='thinman' post='1046799' date='Dec 3 2010, 08:47 PM']Does anyone have any experience of these cheap USB oscilloscopes? Are they OK for basic audio frequency diagnosis?

[url="http://www.virtualvillage.co.uk/2-channel-5v-pc-usb-digital-storage-oscilloscope-new-001482-009.html"]Example item[/url][/quote]

I've never used one, but it claims a bandwidth up to 3kHz, which is ok for bass but a bit too low for guitar use. The sampling rate is quoted as 4kHz, which means the highest frequency it can display accurately is 2kHz, even more limited. Once you've bought it you would need some kind of probe, proper ones cost more than the device does, so that puts the cost up again

I use a Hitachi 100MHz scope, so I'm spoilt a bit, but I'm not sure it is as big a bargain as it seems.

[flyfisher]

The specification states the 'measurable frequency' to be 0 to 3kHz, so no, not really much use for audio work.

PC-based test instrumentation is becoming more and more popular these days though, so you shouldn't be put off the concept as such. There are plenty of similar products that will handle audio frequencies, and far more, but not for £17.99.

[thinman]

[quote name='BanditSid' post='1046851' date='Dec 3 2010, 09:35 PM']I've never used one, but it claims a bandwidth up to 3kHz, which is ok for bass but a bit too low for guitar use. The sampling rate is quoted as 4kHz, which means the highest frequency it can display accurately is 2kHz, even more limited. Once you've bought it you would need some kind of probe, proper ones cost more than the device does, so that puts the cost up again

I use a Hitachi 100MHz scope, so I'm spoilt a bit, but I'm not sure it is as big a bargain as it seems.[/quote]

I noticed the max frequency range and sample rate too. I can't imagine that at that sample rate the shape of higher frequeny waveforms is very well represented.

Think I might have to stretch to a Picoscope of similar.

[icastle]

[quote name='thinman' post='1046862' date='Dec 3 2010, 09:43 PM']I noticed the max frequency range and sample rate too. I can't imagine that at that sample rate the shape of higher frequeny waveforms is very well represented.

Think I might have to stretch to a Picoscope of similar.[/quote]

I couldn't justify purchasing a dedicated scope for the amount of use it would get so I bought one of the Pico ones quite a few years ago.
Still going strong and has a reasonable spec.
I haven't looked into it but I wonder if the limitations of the USB ones are related to the overall spec of USB as a transmission protocol?

[flyfisher]

[quote name='icastle' post='1047047' date='Dec 4 2010, 01:58 AM']I haven't looked into it but I wonder if the limitations of the USB ones are related to the overall spec of USB as a transmission protocol?[/quote]

Not really.

The USB interface will definitely limit the real-time display ability of these instruments, but that's not really the point of a digital storage oscilloscope, which is to catch and display fast and/or transient events. Thus, with fast enough sampling circuitry and a large enough memory, a DSO can collect very fast events indeed. Formatting and sending the captured data to a PC screen for display is not a time-critical process. After all, plenty of professional 'scopes have printer outputs, which have even slower data connections.

The only real difference between USB 'scopes and 'professional' types is that the capture and display sections have been separated and the analysis/display functions are now performed on a PC. This makes a lot of sense because the only really specialised part of a DSO is on the signal capture side of things, so why pay extra for analysis and display capability when PCs are so widely available. It also opens up the possibility of custom analysis software for more specialist applications.

I'd be interested to know why the OP wants to look at audio waveforms though. Apart from determining the peak amplitude of a signal, there's not a lot of useful information to be gained by watching a real-time audio signal on a 'scope. If it's just amplitude info that's requred, then low-bandwidth sampling combined with an averaging algorithm would probably do the trick.

[thinman]

[quote name='flyfisher' post='1047234' date='Dec 4 2010, 12:04 PM']I'd be interested to know why the OP wants to look at audio waveforms though. Apart from determining the peak amplitude of a signal, there's not a lot of useful information to be gained by watching a real-time audio signal on a 'scope. If it's just amplitude info that's requred, then low-bandwidth sampling combined with an averaging algorithm would probably do the trick.[/quote]

Basic fault finding really - e.g. see if a power rail has ripple on it, check a signal fo clipping, funny harmonics. Agreed, it matters not if the signal is delayed but I think it necessary to be able to see the signal accurately represented.

[Subthumper]

[quote name='thinman' post='1047501' date='Dec 4 2010, 04:21 PM']Basic fault finding really - e.g. see if a power rail has ripple on it, check a signal fo clipping, funny harmonics. Agreed, it matters not if the signal is delayed but I think it necessary to be able to see the signal accurately represented.[/quote]

Hi, does it have to be a USB? If its only for what you've listed then why not look for a bench one second hand. I recently picked up an old British made one (vintage it has valves) for twenty quid off of gumtree. Also the other consideration worth looking at in the scopes spec's is maximum input voltage. I looked into USB scopes when my old one died but found that many had only a low max voltage which would be a setback if you ever want to use it on any valve equipment (though many a time I would love to stick 500+volts into a computer).
Just my thoughts.
Cheers Just

Edited December 4, 2010 by Subthumper

[flyfisher]

[quote name='thinman' post='1047501' date='Dec 4 2010, 04:21 PM']Basic fault finding really - e.g. see if a power rail has ripple on it, check a signal fo clipping, funny harmonics. Agreed, it matters not if the signal is delayed but I think it necessary to be able to see the signal accurately represented.[/quote]
A 3KHz bandwidth would be OK for some basic fault finding but the limitations could could quickly become frustrating. For example, you'd see mains ripple on a power rail but not the sort of noise typical of switched-mode PSUs. Similarly, signal clipping could be checked (up to about 3kHz anyway) but it's unlikely you'd notice, or trace any 'funny harmonics' with such a limited instrument.

I haven't checked recently, but I would think that used CRT 'scopes would be a bargain in these days of DSOs and USB-based 'component' 'scopes.

Fortunately, my old 4-beam 150MHz Tektronix analogue 'scope is still going strong. To be honest, I rarely use it these days but I'd find it hard to give up the option of using it in those instances where it's really necessary to 'get stuck in' and have a look at what's really going on. Such things are rarely needed, but invaluable when they are.

[thinman]

[quote name='Subthumper' post='1047866' date='Dec 4 2010, 11:39 PM']Hi, does it have to be a USB? If its only for what you've listed then why not look for a bench one second hand. I recently picked up an old British made one (vintage it has valves) for twenty quid off of gumtree. Also the other consideration worth looking at in the scopes spec's is maximum input voltage. I looked into USB scopes when my old one died but found that many had only a low max voltage which would be a setback if you ever want to use it on any valve equipment (though many a time I would love to stick 500+volts into a computer).
Just my thoughts.
Cheers Just[/quote]

Useful contributions all - thanks. No, it doesn't have to be USB - I'm sure I could find room in the garage for a bench unit. I'll have a look on ebay etc to see what's about.

Good point about the max input voltage - I do have some valve gear.

[tauzero]

It might be worth looking at the DSO Nano - just google for it. They go on ebay (new) for around the £50 mark, and I've been quite tempted (but for the lack of a spare £50). I do have a couple of small bench scopes, but zero bench space...

[thinman]

[quote name='tauzero' post='1057424' date='Dec 13 2010, 03:32 PM']It might be worth looking at the DSO Nano - just google for it. They go on ebay (new) for around the £50 mark, and I've been quite tempted (but for the lack of a spare £50). I do have a couple of small bench scopes, but zero bench space...[/quote]

You selling?

[Arkless Electronics]

"there's not a lot of useful information to be gained by watching a real-time audio signal on a 'scope." I beg to differ!!!!
There is almost all the information you would need....
You should be able to pick up a 20MHz scope for £50 or so that will be SO mush better than a USB type
Jez.

[BigGuyAtTheBack]

Go on the old evilbay and get yourself a proper scope for £50 or so. Far better. Theres plenty there for reasonable bucks.

[flyfisher]

[quote name='Arkless Electronics' post='1061419' date='Dec 17 2010, 11:00 AM']"there's not a lot of useful information to be gained by watching a real-time audio signal on a 'scope." I beg to differ!!!!
There is almost all the information you would need....[/quote]

By 'audio signal' I meant a real-life audio waveform (e.g. music), not something from a test signal generator.

Sure, it's easy to check the peak amplitude of a music waveform but that's about it really. For any serious testing of an audio circuit you'd need to use a signal generator to inject a consistent, reliable waveform, not something all over the place such as music.