Building a Cheap Oscilloscope Using Your PC?

JohnMadison asks: "As a engineering student, I have a lot of projects, but not much test equipment at home. I was wondering if anybody has advice on using my PC as an oscilloscope. I've downloaded a couple of shareware programs that use the sound card for input, but they weren't really useful. I am looking for a good way to make a cheap, yet decent scope. Any sugestions?" While something like this would be an interesting hack, I'm at a loss as to what you would use for probes. The submitter mentions using the sound card as an input, but would that be the best solution? If you were going to make a custom add-on to the PC to do this, what would it need? Does such an add-on already exist? Interestingly enough, this fits in well with an earlier article we did.

Comments

Need better inputs!

[multipartmixed]

The sound card might offer reasonably sensitive voltage comparisons in the 1V range, but really wouldn't be an ideal way to go, IMHO.

Looking at the game ports (two ADCs each) might be one option, and probably "safer". (Game boards are practically free).

Another might be look at the tape port. You have a true IBM-PC, don't you? :)

Parallel Port

[JMZero]

I built one a while back out of a A/D chip and a few transistors. The only other part was a clock chip and crystal. I didn't bother to sync everything perfectly - I just let the clock chip flap away and read whatever was on the lines.

Worked pretty well. It even worked as a video in(though it didn't get much resolution).

This is a really fun project if that's what you're looking for - and it's good enough for simple electronics. You'll certainly be able to see simple wave shapes. That said, you'd have to do some work if you were

1. Were worried about accuracy
2. Needed fast sampling
3. Deal with large ranges of voltages. Mine dealt only in 0-5 volts.

-Dave

xoscope, BitScope

[rrwood]

Some specific links:

xoscope - a software oscilloscope

BitScope - hardware black-box oscilloscope that you control via a PC

Xoscope is Open Source, so hack away if you don't like something about it. The SourceForge page has links to a schematic you can build to use your soundcard as the ADC, though you are of course limited to about 20kHz signals (stereo input = dual trace though). Definitely a cheap way to go.

The BitScope is a really cool design that is open or free (as in beer and speech). You can download all the specs and build it yourself, or buy preassembled kits or BitScopes (cheaper than buying the individual parts yourself). It is a black box that you control via software on a PC, which is pretty cool.

And then, you can always snag a scope on EBay for a couple of hundred bucks. Loads of Tektronix scopes, etc. Wish I could afford a Fluke ScopeMeter myself.

-Roy

Idea

[jrockway]

I was going to build something like this a while ago, but I haven't had time. Just get a A->D chip, hook it up to a USB bridge, and read it a certain number of times a second (500, I think; most D/A converters can handle this IIRC). Connect a probe, voltage limiting circutry, and ground (and a timer, so your software doesn't have to raise the read pin 500 times a second :). Since it's USB, you can easily have another device in the box that does D/A and transposes it on a higher voltage. Then you have an osciloscope and a frequency generator. I think I'll start drawing some diagrams and investigating the IC's. Email me if you want information.