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How To Make A Free PC Sound Card Oscilloscope

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Free PC oscilloscope - Is it possible?

PC sound card oscilloscope trace

This article has been so popular that I've written a whole book about it. The book shows you exactly how you can build the scope into a nice enclosure so that you can conveniently use it on all of your projects.

I've also included a project which adds two additional features that allow you to generate signal waveforms using the headphone output and to calibrate the scope so that you make absolute amplitude measurements. The book is available now in kindle format from here: Sound Card Oscilloscope - Build Better Electronic Projects

The oscilloscope is the single most useful piece of electronic test equipment but it took me years to save up for one. It was a very expensive item back in the 1960's.

The most inexpensive yet usable PC based oscilloscope that I've come across is the Hantek 6022BE USB scope. It isn't perfect but it is incredible value for money and great for the hobbyist or anyone that has need for a small portable scope.

If you can't afford to buy even the cheapest scope available then try building one for yourself by following this project. It won't do as much as the USB oscilloscope but it will cost you very little to construct.

You are so lucky to live in a time where personal computers are so readily available. I'm betting that you either have one of your own already or you have the use of one fairly readily. If you are still at school then you need one for your homework right? If you are not in school then you need a PC to do pretty much everything there is. I am going to show you in this project how you can build yourself a very inexpensive add-on for your PC that will turn it into a very simple but useful oscilloscope.

To keep the cost down to rock bottom I am going to present the simplest PC based scope probe that you can imagine. I made mine using parts from my electronics junk box so to me it comes for free. Don't worry if you don't have a junk box, you soon will do if you start building electronics projects.

So what's the catch? You can't build an oscilloscope for free can you? Well yes you can pretty much. Just so long as you accept that there will be limitations. You are not going to get the same capabilities that you might expect if you went out and spent good money on test gear but if you can't afford to do that and you have no other way of looking at electrical signals produced by your circuits then this project might work magic for you.

The limitations of the sound card oscilloscope are mainly the microphone or audio line input of the sound card that comes with your PC. This means that it will only be capable of displaying relatively slowly moving low frequency signals and the input levels must be kept very low.

Audio sound cards are designed for handling audio surprisingly enough. To handle that job effectively they only need to have a bandwidth of 20kHz because that is the limit of the human ear. Most people can not hear anything at all past that point even if some animals are able to. Also the microphone input is only designed for a 10mV input signal so we must try to keep the input levels low. If you have an audio line in input then you should try and use that instead as it will tolerate a higher 100mV input level.

Not all PC sound cards have stereo audio inputs. If your computer only has mono input then you will only be able to display one signal on your oscilloscope. If you have a stereo input then you will be able to simultaneously display two input signals which is a very useful feature.

I found several software applications that can be used to turn your PC into an oscilloscope and I opted for a free one. Not only will this software turn your computer into a twin beam oscilloscope it will also provide an FFT analysis of the signals too.

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Comments (29)

Topic: How To Make A Free Sound Card PC Oscilloscope
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Saurabh (India) says...
Hi Steve :)
Can I use the above PC Sound Card based oscilloscope to display the ECHO & TRIG waves of an Ultrasonic Sensor Module(HC SR-04) ?
I see under your other project(s) on this website you are using HC SR-04; So I assume that you are better aware of the details for the same.

29th August 2015 1:21pm
Steve (UK) says...
Hi Saurabh, The trigger pulse of the HC SR-04 is a minimum of 10 micro seconds which will not be easy to see with the sound card oscilloscope with a maximum bandwidth of 20kHz. However the trigger pulse doesn't have to be that fast. I used a trigger pulse of 50us in the project that I published on the site. At 50 micro seconds the pulse is just detectable by the scope. It won't look very square of course but you can detect it's presence which is usually what you want to see. You ... Read More
29th August 2015 5:44pm
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Pokke (US) says...
I just made a scope semi following your schematic from the book but used electrolytic 1uf caps and a 5k pot.
it seems to work right. I have been meaning to ask what the difference is between the poly box ones you use and the ones I used.
still much to learn, but having a great time with your book so far. now on to building the cali/generator. thanks Steve
29th June 2015 10:32pm
Steve (UK) says...
Hi Pokke, Using an electrolytic input capacitor is not a good idea. Worst case the capacitor could explode if you apply voltage in the wrong direction. It is more than possible that you will be applying AC signals to the probe that swing both '+ve' and '-ve' which may cause the capacitor to malfunction. Electrolytic capacitors work best when there is a DC bias across them. The terminal marked with a '+' should always be positive with respect to the '-ve' end. ... Read More
4th July 2015 2:29pm
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Don Burke (US) says...
Could you clarify a few things? I was looking at the one that Make did that is a copy except for the values and yours. There are 3 wires for the input and 3 for the output. So one is common on the input and one on the output. Your diagram shows 4 inputs and 3 outputs. on the input, I am guessing the v1- and v2- are the common ground. On the output, I am guessing the same is true, v1- and v2- are common ground and the v1+ and v2+ are separate on the plug to the sound card. Which pin on the ... Read More
24th May 2015 3:37am
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mike baker (UK) says...
Hi Steve,

Would this be suitable for reading a signal going to a moped tachometer?

The cable is wrapped around the spark plug wire.

Many thanks,

30th April 2015 9:52am
Steve (UK) says...
Sorry for the delay in replying. Auto ignition systems generate many thousands of volts and even one turn of wire around the ignition lead could induce very high voltages. For this reason I would say do not attempt this unless you are very confident that you know what you are doing. Worst case you could damage both the probe and your PC.

4th July 2015 2:13pm
João Alves (Portugal) says...
Hi Steve!

Unfortunately Amazon tells me that your book is not available for my country (Portugal).

I wonder if there is any other way to get it.

Thank you.
7th April 2015 8:30am
Steve (UK) says...
Hi João,

I'm very sorry that you are having a problem. Having just done a little research there appears to be some kind of copyright issue going on with Amazon purchases of ebooks in Portugal. I have no idea what it could be.

Some people have had success by buying from the amazon. com or . co. uk sites. You might want to try that. If you still have a problem then send me a message using the contact form (link at the bottom of this page) and I will see what I can do to help.

7th April 2015 9:34am
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sameh (Egypt) says...
its realy use ful thank you but i want to know the kind of the wire we use it to take the signal into the pc and its the most famous kind of it
20th February 2015 2:30am
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