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How to use sound card as PC oscilloscope?

By potoole
Jan 4, 2008
  1. Hello, I just joined this forum and I need some advice or info. on inputing external signals to my PC sound card at the microphone jack.

    I downloaded software that makes it possible to use my PC as an oscilloscope. The PC sound card is used to input sounds and other data, and the voltage pulses can be viewed on the PC oscilloscope. It takes sounds from a microphone and displays the sound frequencies as voltage pulses.
    The microphone input can also be used to input other signals from external electronic circuitry - BUT there is a need to be careful not to input voltages that are too high. The software developer states that the input line voltages need to be 0.7volts or less, and a seperate circuit should be used to attenuate the inputs.

    I have a Realtek HD audio input in my PC, and I guess that is the sound card. Can anyone tell me what are the required (safe) input voltages to that type of sound card at the microphone input? The mic. input is a 1/8" jack on the front (or rear) of the PC.

    Thank you
    potoole
     
  2. kimsland

    kimsland Ex-TechSpotter Posts: 18,353

    More information required
    Card Manufacturer, revision, type any other info on the card
    Also your M/b (unknown) and Power Supply (unknown) may change or fluctuate the sound card's voltages (tolerance unknown)

    I don't believe that you will get a true reading without actually spending big bucks on linguistic sound measuring machines. The computers usually just hold the data.

    Even if you post back with all the above info, I personnally still can't help, possible someone else may give more info.
     
  3. captaincranky

    captaincranky TechSpot Addict Posts: 10,814   +921

    A Mic. is a Mic. is a Mic.? Not really....

    Microphones vary in "sensitivity". This is possibly self evident in that the voltage outputted will be quite different when you're whispering, as opposed to when you're screaming into it. To use a Mic in the way you're suggesting, I would put it into a mixer and introduce it the computer at the line input.

    The controls of a a normal oscilloscope allow for setting the range of measurement. IE; .50 Volts Peak to peak, or 50 volts P-P. To suggest that this program requires a max input of point .7 volts is to say that it misses the whole ranging stage of a normal instrument. or ? as I'm not sure how that last sentence should end. Oscilloscopes are used in a variety of applications which reqiure either amplification, such as an electrocardiogram where fractions of a millivolt are important, to finding out which sparkplug in your car is not firing where the primary signal source is as much as 30,000 volts. Here attenuation is necessary, usually via a magnetic pickup device.

    Line potential is normally about 1 Volt P-P I believe, but here again it is dependent on how hard any given signal source is driving it. Yanni less than a volt, Metallica, way more.

    It's not exactly clear what you're trying to accomplish. If it's just for the heck of it simply turn down the mixer output and load the program, turning up the mixer until it seems to fill (vertically) the display.

    Incidentally "Nero Mix", (available in Nero 6 and above), has an oscilloscope display in it's mixing console, I'm not sure if it can be used in real time.
     
  4. potoole

    potoole TS Rookie Topic Starter

    What does sound card with 7.1 cabability mean?

    My sound card doesn't have a "line in" input. I need to input thru the mic jack, I guess.
     
  5. captaincranky

    captaincranky TechSpot Addict Posts: 10,814   +921

    It Might......

    "7.1 sound indicates 7 discrete channels of sonic information, and the .1 is the LFE (low frequency effects), alias subwoofer.
    The 7 channels are L front, Center, R front, then L side, R side, L rear and finaly R rear.

    Sound cards normally have what are called "retasking" jacks. So, you may have to open up the control panel (of the sound card) to figure out which jack currently doing which job.
     
  6. Dave.r123

    Dave.r123 TS Rookie

    I have also been trying to develop one of these devices, i think potoole wants to do something similar to what I'm trying to accomplish which is to just take in two channels of input from some circuitry probably low power no more than about 12v max and be able to capture the waveforms with the software. Possibly calibrated to accurately measure voltage. This device would be connected via line-in or mic to the computer. These two inputs must have some sort of standard acceptable operating voltage range. What i need help with is some advice as to what kind of circuitry is required to keep the sound card safe from overload and what circuitry i need to use to reduce the input to a safe range for the card.
     
  7. Dream-

    Dream- TS Rookie

    Reading from the responses it seems that no one has understood what you are asking (except for the last poster who is basically asking for the same).

    A sound card oscilloscope will give you around 100KHz bandwidth, which is usable for most audio signals and it is a good usable range for analog electronics. It has 3 basic problems:

    1) Sound cards are AC coupled, meaning that you will not be able to read signals with frequencies lower than around 10Hz. Also anything lower than 20Hz will get distorted by the AC coupling capacitor.
    2) Sound cards have an input impedance that varies around 1KOhm. This means that a circuit with a small signal will get sucked up and you will not be able to read it. (but we can fix this with a pre amp)
    3) Sound cards can only safely read around 1.3V peak to peak (we can solve this by scaling the signal)

    If you just want to solve #3 and get safe signals to put into your sound card here is a simple solution:

    www .electronic-engineering.ch/radiocontrol/circuits/osziconn/connect.html

    If you want to solve the impedance problem here is a simple follower circuit:

    www .geocities.com/~uwezi/electronics/projects/soundcard_osci.html#operating

    You can search the net for software oscilloscope software, there are plenty of them.

    Here is a research write up on the topic that may or may not be of use to you: www .qsl.net/om3cph/sb/dcwithsb.htm

    Hope this helps.

    PS Since I can't yet post links, make sure you remove the "space" between the www and the "." in the above links.
     
  8. SNGX1275

    SNGX1275 TS Forces Special Posts: 12,626   +320

    Thanks for the post (I think)..

    I obviously am not an sound expert, but could you explain your #1? Everything in a PC runs on DC, so talk of AC confuses me.

    I think I have a couple other concerns with what you said, but I don't have enough coherent thoughts to post them yet.
     
  9. Dream-

    Dream- TS Rookie

    Alternating Current or AC is any signal that oscillates between the positive and negative poles. All audio signals are AC, like the ones that come out your speaker jack, or go into your mic jack.

    If you put a capacitor in series with the input line, only AC signals can get through, any DC is cutoff. And depending on the size of the capacitor, you can know what frequency is the minimum to be able to go through the capacitor. This is done to protect the audio card electronics from a DC voltage bias that may enter and fry the circuits.

    So if your signal is not oscillating faster than around 10Hz, it will not get through the sound card and you will not be able to analyse it. Furthermore, at low frequencies, the capacitor acts as a filter and will distort the signal waveform.
     
  10. Justin

    Justin TS Rookie Posts: 1,595

    Dream is pretty correct in his information. The incoming signal to the input line on the sound card will be an AC signal

    Keep in mind though that most modern sound cards use hardware DSPs to convert the signal, and what's traveling across the PCI bus will be fully digital- the signal waveform is recreated in software to give you an idea of what you're seeing. Everything you want is on the soundcard itself.

    A sound card is a poor choice to use as an oscope.

    Why are you trying this, anyway?
     
  11. McDavid

    McDavid TS Rookie

    This sound card oscilloscope probe seems to be able to solve the problems of impedance matching, over-voltage protection, limited measurement range. etc.

    virtins.com/Virtins_Sound_Card_Oscilloscope_Probe_Manual.pdf
     
     
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