Connect with us

Anyone made a sound card oscilloscope?

Discussion in 'General Electronics Discussion' started by Robert Hill, Jul 7, 2015.

Scroll to continue with content
  1. Robert Hill

    Robert Hill

    111
    12
    Mar 5, 2015
  2. Arouse1973

    Arouse1973 Adam

    5,164
    1,078
    Dec 18, 2013
  3. Robert Hill

    Robert Hill

    111
    12
    Mar 5, 2015
    Thanks for the link. I'm going to buy to bits for the one on the make website and post how I get on.
     
  4. Steve Garratt

    Steve Garratt

    23
    5
    Jul 22, 2014
    Hi Robert,

    The article on the makezine.com site was based on a project on my website here http://homediyelectronics.com/projects/howtomakeafreesoundcardpcoscilloscope/ You will notice that the video on the make site mentions me as the originator. I have also written a book that is available on Amazon Kindle details here http://homediyelectronics.com/books/soundcardoscilloscope/ The book goes further to describe how to build the scope into a box and to build a calibrator to go with it.

    I hope that you have fun building it.

    Regards
    Steve
     
    Gryd3 likes this.
  5. Martaine2005

    Martaine2005

    2,508
    670
    May 12, 2015
    When you build it, they will come. Amen.
     
  6. Robert Hill

    Robert Hill

    111
    12
    Mar 5, 2015
    Hi Steve, just got your book and ordered all the bits for the oscilloscope. I'll try to put updates as I go.
     
    Arouse1973 likes this.
  7. Steve Garratt

    Steve Garratt

    23
    5
    Jul 22, 2014
    Hi Robert,

    I hope that you like the book. Let me know if you need any help.
     
    Arouse1973 likes this.
  8. Robert Hill

    Robert Hill

    111
    12
    Mar 5, 2015
    I had a thought about whether you could use a voltage controlled oscillator, hooked up to the oscilloscope input and controlled by the dc voltage you wanted to sample to get round the ac coupling on the sound card. I know you'd be creating an ac signs from the dc voltage but if you knew how the vco reacted at set voltage levels you could work out what the ac signal represented in terms of dc input. Maybe you could even get a programme to do the maths for you and represent it visually. I'm not an expert obviously so maybe what I've just said is stupid but thought I see what others thought.
     
  9. Robert Hill

    Robert Hill

    111
    12
    Mar 5, 2015
    Hi Steve, I've had a read through the first part of the book and hopefully getting my components tomorrow.

    I wanted to ask a few things:

    What is the purpose of the negative terminals which are connected to the ground rail in the terminal blocks where the probes are attached? As far as I can see nothing is actually connected into these negative terminals from outside the project box (like probes etc). I know the positive terminals on these blocks have the circuit probes connected. I suppose the question is why are they connected to the ground rail?

    Is the function of the connection to the ground in the circuit to provide a route for excess current created when the diodes need to open up to limit voltage? I.e. if voltage limiting were not needed could this part be omitted altogether. I feel like it could not as I know production oscilloscopes have a ground connection probe too. I think it may be that the connection to ground is there so that the potentiometer forms the voltage divider along with the 470k resistor. So the 100:1 divider you mention in the book is the series resistance of the 470k resistor plus the 4.7k from the 'top' half of the potentiometer against the 4.7k of the 'bottom' half of the potentiometer which is linked to gound. Is that right?

    Can the signal generator in the second part of the book be used to generate signals to input into other circuits that I might make e.g. can it create square wave, triangle waves and the like?

    Sorry if these are all noob questions. I like to understand things as otherwise I won't be able to do things on my own in the future.
    Thanks,
     
    Last edited: Jul 10, 2015
  10. Alec_t

    Alec_t

    2,722
    723
    Jul 7, 2015
    As an alternative to using a VCO, you could try using the DC level to create a PWM signal. Might be simpler/cheaper, depending on how linear/accurate the result needs to be.
     
  11. Robert Hill

    Robert Hill

    111
    12
    Mar 5, 2015
    Got my parts in and made a mock up of the circuit on the breadboard. There's also a picture or my first wave captured on the computer. WP_20150711_11_04_28_Pro.jpg WP_20150711_11_21_07_Pro.jpg WP_20150711_11_36_42_Pro.jpg
     
    Arouse1973 likes this.
  12. Steve Garratt

    Steve Garratt

    23
    5
    Jul 22, 2014
    Hi Robert,

    Don't worry about asking questions. Nobody knows everything, me included.

    In order to measure an electrical signal you need two connections to complete the circuit. A ground or negative connection is generally used to create the connection. So to display an AC signal you would connect the ground of the probe to the ground or negative side of your unit under test and use the positive connection to probe the signals in your circuit.

    The voltage limiting is there to help protect your PC against inadvertently applying too high a voltage to the probe. Please remember that it will not protect you if you apply very high voltages so you should stick to signals below 30V to be on the safe side.

    The signal generator can indeed be used for purposes other than calibrating your oscilloscope probe. You can use it for instance as a convenient signal source when testing audio amplifiers. By injecting a known waveform into the input of the amplifier and monitoring both the input and the output with the oscilloscope you can not only see how much gain the amplifier is providing but also how faithfully the circuit reproduces the wave shape at the output.

    Steve
     
    Arouse1973 likes this.
  13. Robert Hill

    Robert Hill

    111
    12
    Mar 5, 2015
    Here's a few shots of the finished article. It's nice to make something which looks professional and putting it in the enclosure really does that well. WP_20150714_20_35_30_Pro.jpg WP_20150714_20_41_38_Pro.jpg
     
    Arouse1973 likes this.
  14. Robert Hill

    Robert Hill

    111
    12
    Mar 5, 2015
    I've hooked up the osciloscope to my arduino with the basic blink program running and got the following wave form:
    upload_2015-7-15_20-17-13.png
    I was expecting something more like a standard square wave as the LED goes on for a second then off for a second. It also seems like the wave dips when the LED goes on and rises when it goes off. Any ideas what is going on?
     
  15. Arouse1973

    Arouse1973 Adam

    5,164
    1,078
    Dec 18, 2013
    Being the input to a sound card doesn't the input have to be A.C? Not sure if you can measure D.C. Looks like the signal is going through the input capacitor on the sound card.
    just a thought
    Adam
     
  16. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

    4,960
    648
    May 8, 2012
    Exactly Adam. Looking at the scope trace it appears his Aduino freq is 1Hz. This freq is far too low to faithfully AC couple a square wave signal to the sound card.

    It might be prudent to explain the limitations of a Sound Card Scope because they are many. This is an entry level (home experimenter grade) instrument only!

    Chris
     
  17. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

    4,960
    648
    May 8, 2012
    Robert, take a look at the spice simulation I provided for you. It's comprised of a square wave signal source and an RC coupling network that will look much like the coupling network (but not exactly) on the MIC input circuit of your PC.

    The first plot is generated using a 1Hz square wave, 0 to 1V.
    The second plot is generated using a 1KHz square wave, 0 to 1V.

    Do you see what's happening here?

    Chris
     

    Attached Files:

    Arouse1973 likes this.
  18. Arouse1973

    Arouse1973 Adam

    5,164
    1,078
    Dec 18, 2013
    One thing you could try is to put a large capacitor in series with the input signal of the circuit before the diodes. I would start with 4700 uF 16V and see if that improves matters. The reason this is happening is the RC time constant of the input to the sound card is too short for such a low frequency.
    Adam

    Edit: This is complete bollocks! :D about the capacitor helping.
     
    Last edited: Jul 16, 2015
  19. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

    4,960
    648
    May 8, 2012
    Adam, I don't think that's going to help. The DC blocking cap in the PC is still a major (LF) limiting factor. After all, you can't increase capacitance by adding a cap in series with another cap. It does the inverse and reduces the total capacitance. EG two 1uF caps in series = .5uF. ;)

    Chris
     
  20. Arouse1973

    Arouse1973 Adam

    5,164
    1,078
    Dec 18, 2013
    Oh god, what am I thinking, why on earth did I think capacitor in series add....yes sorry Chris. :oops: Better get my electronics for dummies book out.
    Adam
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-