oscilloscope using audio line in on laptop

[Soundshark]

I was having a think late last night about saving my self some money and getting a second hand oscilloscope but then an idea hit me what if i reduced the voltage all way down between 0.4 - 1V, that would be at line level accepted by standard audio equipment. Now i could then connect this to a notebook running free audio software to record the wave or see in real time. i understand its not going to be as simple as just stick a transformer in there but i do think it may be a viable option.

I would really like your thoughts on this and any ideas you may have to implement it

Thanks

Anthony

 

[LTX71CM]

It's done all the time. People have been (trying) to use their audio cards as an oscilloscope for years, It does work to some degree but is obviously very limited. For most audio cards you're limited to probing circuits under 22kHz, very slow. If you're working with low speed signals it could work beautifully for you, or it may not. If you do as mentioned and protect your audio card by limiting both incoming voltage and current it doesn't hurt to try for yourself.

 

[barathbushan]

I Think most cards sample at 44.1kHz and 16 Bit resolution , 22khz is way too old ,trust me i have done PC scope and used this software

http://www.zeitnitz.de/Christian/scope_en

Its a grand flop !!

the waveforms are distorted as hell , there is no stability , and you cannot obviously measure the amplitude , and worse if your input exceeds 1V , you have the chance of frying your soundcard attached to the motherboard
yes you can use it once in a while if you are desperate , BUT IT CAN NEVER REPLACE A STANDALONE SCOPE

 

[Soundshark]

Im pretty new to all this so im mainly working digital at the mo so it would only be to read off pulse timings really but i would be using a 64 audio card so i would be able to get a much better range of readings i think im going to buy a scope for future use as there are a few going cheap on ebay (must need the cash for crimbo) but also build this idea anyway for the sake of learning, Is there any links to and existing project you guys know of?

 

[barathbushan]

Is there any links to and existing project you guys know of?

This is the best reference for cheap oscilloscpes

http://www.opencircuits.com/Oscilloscope#some_low-cost_oscilloscopes

I know the link will definitely help you

 

[(*steve*)]

Here is another option. If you do some searching you'll find that they have three options, calibrated, un-calibrated, and without probes.

Not really a substitute for a real scope, but handy and portable.

If you're interested I can connect one of these and a better cro to a signal generator so you can see what you'll get.

 

[JimW]

If you are going to use it for digital data only, then you are really looking for a logic analyzer. Google: "parallel port" logic analyzer and you will find some simple 8 bit analyzers for looking at digital timings. Good up to about a megahertz or so.

-Jim

 

[(*steve*)]

I had a bit of fun yesterday comparing the display on my 60MHz scope to that of the 1M sample/sec digital scope.

One major difference is that the line is a constant width and density on the digital "scope". You can't get the sense of a fast rise time by looking for faint or invisible leading and trailing edges.

With sine waves (as expected) the digital scope seems to perform pretty well up to about 100kHz before the waveform gets really distorted (and aliasing occurs soon after)

With square waves, the waveform looks OK up to about 40kHz.

The advantage of the digital scope is that voltage and frequency measurements are far easier.

I think that for audio work it would be fine.

The fact that a friend of mine thought it was an app for a phone (he asked me what sort of android phone it was) gives you some indication of it's obvious portability.

Digital signals....? Dunno. Certainly not for anything with a clock frequency above audio frequencies. I guess that limits you to stuff running from 32768Hz crystals

Battery life? Well, I left it running for about an hour and the battery (which wasn't fully charged to begin with) is only down to about 60%. It's pretty new, the battery will age, but not bad. It charges from USB, and you can't operate it while it charges.