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PC Sound Card Probe Test Points

Building the Sound Card Oscilloscope

Before you build the project here check out my book: Sound Card Oscilloscope - Build Better Electronic Projects. It contains a slightly better circuit for the probe plus additional circuitry for calibration and a signal generator.

If you want to buy a cheap but inexpensive USB based oscilloscope then you could do worse than the Hantek 6022BE USB scope.

PC sound card scope probe board

This is a very simple circuit that can easily be built on a small piece of perforated matrix board. I used a piece of board that had no copper at all but you can use one that has isolated copper pads around each hole just as easily.

The way that you build your probe will depend on what type of potentiometer you decide to use. I had some large trimmer variable resistors in amongst my junk but you can use any type of trimpot or panel mount controls just as easily.

Each of the two channel circuits are identical and can be built on the same board next to each other as in the picture.

Making test point posts

Input and output cables should be attached to wire posts on the edge of the board for convenience. You can buy proper posts that fit into the holes in perforated board if you want to. I have some of these test point posts and frankly I think that they are more trouble than they are worth. I would rather make my own and this is how you do it.

22 guage solic copper wire

I used 22 SWG (21 AWG) wire from a reel that I have had for some time but you can strip the insulation from solid connecting wire if that's all you have.

This guage of wire is 0.7mm (0.0275inch) as measured on my digital caliper

copper wire held by pliers

Cut a length of wire approximately 70mm (2.75inch) and hold it in your Long nose pliers roughly half way down the nose. The width of the pliers at this point will determine the size of the loop at the top of the post.

Copper wire bend around pliers

Gently bend the wire around the pliers to form a loop at the top with the 2 ends of the wire making the post.

Finished home made test post

This is what the finished post should look like. With practice you can make these very quickly and you can vary the length and the size and shape of the loop at the top to suit your needs.

Home made test probe in board

You may find that it is a tight fit getting the double width wire post through the holes in the board. I managed it by squeezing the wire together in a pair of pliers. You can also enlarge the hole slightly by running a small drill through it. The holes in some boards may be larger than others.

If this post doesn't work for you then try the alternative method below.

Home made test post alternative

If you have trouble feeding two wires through one hole then you could try this alternative post that uses 2 holes in the board but avoids having to enlarge holes.

Alternative post in 2 holes on the circuit board

Insert the alternative post into 2 adjacent holes and bend to secure.



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Comments (45)

Topic: How To Make A Free Sound Card PC Oscilloscope
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Aidan (US) says...
can it handle ac current
2nd December 2017 5:15pm
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venturini patrick (France) says...
SmileHello Thanks for your video . Beccause , befor having enough money tu by a osciloscope , i will try to build the litlle osciloscope .
But cant find the link ( lin adress ? ) tocharge on the computer ( for simulating the 2 channels of a osciloscope ).?
Could you answersto my mail adress ?
Thank
Your
Bes t regards
Patrick Montpellier France
4th September 2017 9:12pm
Novalar says...
Good article!
22nd August 2017 8:40pm
Novalar says...
Thanks! I used this to measure a laser driver stability when switching the current, I was able to see the switch spikes perfectly!
22nd August 2017 7:57am
Dan (US) says...
Can the scope described in the book work with a Linux based software?
30th June 2017 9:05pm
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Sam (India) says...
Hi, this is an amazing idea and this is going to save me a lot of money. I have not yet built this circuit. I have a few questions to get cleared.
1. To which port of my do I connect the output probe to? headphones or microphone or line-in?
2. For my experiments, I may have to operate around a voltage of 15 to 22 volts. Will this pose a threat to my sound card?
9th April 2016 7:33am
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Dave (Australia) says...
Hi, thanks for sharing this build, it's great.
I want to make this oscilloscope to test sensors and wiring on my car, but the cars voltage is between 12v and 14.4v.
Will this work for me?
Or, are there any changes that I can make to the design so that it will cater to my needs?

Thank you. Smile
1st April 2016 10:20am
Steve says...
Hi Dave,

Yes this should work fine providing that you stay well away from the high voltage part of the engine. That will be the spark plugs and induction coil etc. It should work ok for sensors that are likely to be 12v powered. Always Test the signals with a multimeter first. Test for DC voltage and AC voltage and do not use the scope on anything over 30v.

Steve
5th April 2016 9:15am
David Schroeder (US) says...
Is it possible to store a single sweep with this system? Currently I have a Textronix 465B scope, and my experiment setup entails a single sweep for each run, triggered by a specially timed pulse. It's hard to analyze any detail as the image on the screen is so transient. Being able to capture a single sweep and continuously display it would be really useful.
21st January 2016 10:14pm
Steve (UK) says...
Hi David,

I do believe that you can store a single sweep. You can set it for single sweep and get it to trigger somewhere of interest.

Steve
31st January 2016 1:44pm
David Schroeder (US) says...
Is it possible to store a single sweep with this system? Currently I have a Textronix 465B scope, and my experiment setup entails a single sweep for each run, triggered by a specially timed pulse. It's hard to analyze any detail as the image on the screen is so transient. Being able to capture a single sweep and continuously display it would be really useful.
21st January 2016 10:14pm
David Schroeder (US) says...
Is it possible to store a single sweep with this system? Right now I have a Textronix 465B scope, and my experiment setup entails a single sweep for each run triggered by a specially timed pulse. Currently it's hard to analyze detail as image on the screen is so transient. Being able to capture a single sweep and continuously display it would make it really convenient.
21st January 2016 10:09pm
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Keerthana (India) says...
can we implement a phase locked loop using sound card
12th December 2015 4:12pm
Steve (UK) says...
Hi Keerthana,

In theory you could build a phase locked loop by adjusting the output waveform from the headphone socket in real time depending on the waveform input through the microphone input.

I'm not aware of any PLL software for the pc so you would need to write some code to do it. This is way beyond the scope of this article unfortunately.

Steve
12th December 2015 5:26pm
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.

Regards,
Saurabh
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,

Mike
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.

Steve
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.

Regards
Steve
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?

Regards
Steve
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...
thanks
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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