Computer as Oscilloscope

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Michael-love-electronics
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Computer as Oscilloscope

Post by Michael-love-electronics » Tue Apr 19, 2005 9:59 pm

Hi,..<p> I need a CRO and I can buy one, a friend told me that there's a program that uses the sound card as an I/P and the monitor as the O/P.<p> I got the program but what I need to know is:
" are there any limitations concerning the I/O signal.? What are they.? (details please)"<p> Thanks you all your time.

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sofaspud
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Re: Computer as Oscilloscope

Post by sofaspud » Tue Apr 19, 2005 10:17 pm

If you want details you have to provide details. You didn't mention what program you obtained. Its limitations should be stated in the documentation. The main limitations are likely to be from your sound card. Don't expect to view waveforms in the megahertz range. The sound card is designed to process audio signals, 20kHz and below.

ezpcb
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Re: Computer as Oscilloscope

Post by ezpcb » Tue Apr 19, 2005 11:54 pm

cooledit pro can be use as an oscillscope. You can watch, edit and do spectrum analysis with it. The signal bandwidth was limited by the sound card. Most audio codec chips has a digital low pass filter with stop frequency of 20-25k Hz. The acceptable signal level should be limited in 1Vp-p for most sound cards.
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Dean Huster
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Re: Computer as Oscilloscope

Post by Dean Huster » Wed Apr 20, 2005 2:56 pm

Signal analysis using a sound card sounds a little enthusiastic to me. Sure, it can be done, but if the card is limited to 20KHz bandwidth, you'll be limited to around 1KHz for a fundamental waveform frequency if you intend on getting even a few harmonics analyzed. Sound cards are likely AC-coupled, so you can't use them for DC measurements or for low AC frequencies without losing amplitude accuracy.<p>Another limitation will be the input voltage. The card won't respond to really low ones and you'll be limited to maybe 12 volts peak maximum before the sound card either saturates or any input protection clips the signal. A large-enough signal will blow the sound card.<p>You can get some pretty nice, lab-grade, used analog scopes on ebay for reasonable prices. I'm a champion of analog (vs. digital) scopes for most applications. Hey, I prefer manual gearboxes over automatic in my trucks, too.<p>Dean
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Michael J
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Re: Computer as Oscilloscope

Post by Michael J » Wed Apr 20, 2005 3:21 pm

There are several applications around that let
you use your sound card as a CRO input for your computer.<p>The limitations are as Dean and Ezpcb said 1- Bandwidth and 2-Voltage.<p>There is a project available in Australia called
a "soundcard pre amp", was published in the now deceased magazine Electronics Australia Magazine,
but a copy of the article may be obtained through
Silicon Chip Magazine here. This unit has
Gain x 10, x 1, x 0.1, x 0.01 on the inputs, but here again you are limited to the voltage capability of the input transistors, probably
30 to 50 V if that.<p>If you really need a CRO your best option is to
go buy a seconhand one if you don't have much cash. You will spend that much anyway if you start blowing up sound cards and motherboards
using incorrect input voltages.<p>Its a nice thought,, but in reality using a PC
as a CRO is not very practicle. Unless you only
want to look at very low voltage low bandwidth
signals, and don't care about accuracy.<p>Don't Smoke your PC, its bad for their health.

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jollyrgr
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Re: Computer as Oscilloscope

Post by jollyrgr » Wed Apr 20, 2005 4:29 pm

A soundcard will probably only let you input a signal at about 1V peak. But for about $200 (sometimes much less) you can get a USB scope complete with software. Here is one example:
http://www.usbwholesale.com/oscilloscope.htm<p>I do not own the above device nor am I recommending it. I only used the above as a reference of devices that are available. <p>The beauty of these is their isolation. You cannot connect a hardware (CRT) based o'scope to a TV chassis without an isoloation transformer. With one of these computer/USB guys your problem is solved.
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chapter30
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Re: Computer as Oscilloscope

Post by chapter30 » Wed Apr 20, 2005 5:07 pm

I have a thing called a pico scope (brand name) that hooks up to my parallel port. It was cheap, about $60 if I remember right. I don't like it though. The software bogs down my computer and things tend to freeze up a few seconds at a time.<p>I ended up going the route that Dean mentioned...ebay. It did cost me more though. Basically the pico scope was good to get me through my senior project class where I just had to be able to see some very slow waveforms. It is a low cost solution but not lab grade.<p>I going to go dig it out mess with it some more.

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Re: Computer as Oscilloscope

Post by Yerry » Wed Apr 20, 2005 6:20 pm

I've had astounding results with a sound card O-scope since about '95 ( recall at that time refusing to go to W95 because W3.1 was plenty good enough). the O-scope software hadn't come out yet, or I hadn't found it, so I used some audio editing software.<p>Where it worked so well wasn't measuring frequencies but for watching a slowly changing voltage level for some high-speed photographic triggering circuits I had made. I had to account for relay lag as well as the delays inherent in a mechanical to electronic to mechanical to electronic to mechanical shutter chain.<p>IR phototransistor output to one audio channel; shutter output to the other. Measure the difference on the screen with a ruler, calculate the time difference. Tweak the 7555 circuit and try again.<p>With the frequency rolloff and signal filtering, sound cards aren't much good for frequencies higher than a D-cell, but for getting that "there--not there" determination of a signal, they're great. faast as lightning, as my pics can attest.

Michael-love-electronics
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Re: Computer as Oscilloscope

Post by Michael-love-electronics » Wed Apr 20, 2005 9:11 pm

Thanks for your consideration, I'll have to hault the project till I buy a secondhand one.<p> Thanks again

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