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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 (31)

Topic: How To Make A Free Sound Card PC Oscilloscope
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adil (India) says...
instead of pc can i use android based cell phone(smart phones)... you find many app in play store can this circuit support any one can help me out!!
17th November 2015 2:19pm
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adil (India) says...
instead of pc can i use android based cell phone(smart phones)... you find many app in play store can this circuit support any one can help me out!!
17th November 2015 2:17pm
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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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Marut (India) says...
Thank you so much Steve. It is amazingly precise and easy to follow.

I also have a question. You mentioned that it limits op voltage to 500mV. I was planning to use your arrangement for showing the output of an ECG circuit which amplifies heart signal to around 5V at the output. So shall my 5V output signal get distorted if I use your circuit arrangement?

Love and regards from India...
3rd August 2014 2:21pm
Steve (UK) says...
Hi Marut,

Yes you can use it to measure voltages up to about 30V with no problems. The input is attenuated and then clipped to a safe level for passing to the microphone input. Have you built the circuit in this article or did you use my Kindle book?

3rd August 2014 2:47pm
Marut (India) says...
I have used your above article to get an idea about this amazing concept. I am aware of your book on Kindle as well. Hope I can get my PQRST waveform on the PC screen through your circuit.

I was worried that I didn't have an oscilloscope at my disposal. I needed to rely on my college lab for that. Now your post has given me a real boost.Smile
3rd August 2014 3:45pm
Steve (UK) says...
Be aware that the lower frequency limit of the sound card is not much less than 20Hz. This may just be low enough to capture a heart beat but you will need to experiment with that.
3rd August 2014 4:10pm
Marut (India) says...
Roger that Smile
3rd August 2014 4:30pm
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Alessandro (Brazil) says...
Thanks! I used this to measure a laser driver stability when switching the current, I was able to see the switch spikes perfectly!
1st August 2014 11:01pm
Steve (UK) says...
Hi Alessandro, I'm pleased that you liked the project. I think that it's a great addition to anyone's tool kit. You might like to know that I've recently published a Kindle book entitled "Sound Card Oscilloscope: Build Better Electronics Circuits". It is far more comprehensive and shows you how to put it into a neat enclosure to make a permanent job of it. The book also covers building a calibrator to allow absolute amplitude measurements and a signal generator output ... Read More
1st August 2014 11:29pm
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mahmoud (Jordon) says...
30th July 2014 1:37am
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Narendra .K.C (India) says...
i am very grateful to you
27th July 2014 5:22pm
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beppe devercelli (Italy) says...
Really useful and comprehensive.
Thank youGrin
24th July 2014 5:55am
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CT (India) says...
great project! works great
i have a doubt though

How and why are we selecting a 3.3 k ohm and a 470k pot?
19th May 2014 12:07pm
Steve (UK) says...
Hi CT, The input resistor and potentiometer were chosen to provide maximum sensitivity and a degree of overload protection. The small 3.3k ohm resistor limits the current through the protection diodes to about 10mA max. with input signals up to 30V. The 470k ohm pot allows for small signals to be displayed while providing a higher input impedance with larger inputs. I'm currently trying out an alternative arrangement using a 470k ohm fixed input resistor and a 4.7k ohm potentiometer. This ... Read More
19th May 2014 4:34pm
CT (India) says...
oh Ok... got you point. Grin
another point that i was wondering about is how does the two zener diodes work.

P.S. im a noob in electronics :PSad
19th May 2014 4:56pm
Steve (UK) says...
The diodes are just ordinary diodes not zeners. I'm making use of the fact that if you forward bias a diode with a small voltage less than about 0.5-0.6v it will not conduct but if you increase the voltage then it conducts so hard that it will not allow the voltage to rise above 0.5-0.6v unless it burns up with excessive current. Connecting the diodes back to back prevents the AC signal amplitude from going more than plus or minus 0.5-0.6v. The objective is to protect the microphone input ... Read More
19th May 2014 5:31pm
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richard bromberg (US) says...
this question is about the oscilloscope leads.
What is a 3K3 resistor, do you mean a
3K Ohm resistor. excellent article
26th February 2014 1:32pm
Steve (UK) says...
Hi Richard,

A 3K3 resistor is just another way of saying 3.3K Ohms resistor. It's a kind of shorthand. Both types of notation is used widely and probably a few others.
26th February 2014 2:18pm
Ed Hahn (US) says...
3K3 means 3.3k
21st June 2014 9:11pm
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Steve (UK) says...
I used signal diodes with a fast switching characteristic capable of conducting 200mA. Diodes with a higher maximum forward current would give more protection.
17th February 2014 12:54am
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xavier (France) says...
Hello, thank you for sharing, what are the characteristics of D1 to D4 diodes ?
13th February 2014 2:18pm

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