PC Sound Card Function Generator

Discussion in 'General Electronics Chat' started by daddycool, Jan 30, 2011.

  1. daddycool

    Thread Starter New Member

    Jan 30, 2011
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    Hi. I'm wanting to use the sound card of my PC to generate waveforms. This is easy enough, as there's a lot of software that does this... The problem is: How do I physically connect the output to my circuit- that is, which output jack do I use (headphone or speaker jack), how do I connect the wires, confgure the clips, etc?
    I'm a bit new to electronics and know very little about audio equipment. So a very clear explaination from the beginning, and covering every step, would be helpful and much appreciated.
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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  3. daddycool

    Thread Starter New Member

    Jan 30, 2011
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    What I will be connecting to most are breadboarded opamp circuits as these are frequently used in our college labs. So if, for example, I wanted to connect the waveform generator (my sound card) via a standard 3.5mm stereo headphone jack to a 741 in a single input configuration, and using the URL you provided as a guide, would I connect the R or L wire to the input? And what exactly would I connect to circuit ground?
    I apologize in advance if these questions seem a bit naive.
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
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    Ground goes to ground. The R/L connection depends on which channel has the signal you wish to work with. If the signal generator has produces a mono .wav file, the the same information is on both channels.

    We have grown to have a sort of horror about the old 741 op amp. They are very poor performers compared to just about any other op amp. Modern ones are just incomparably better performers. The TI series of TL071 & 081 op amps are quite inexpensive and way better than 741's.
     
  5. daddycool

    Thread Starter New Member

    Jan 30, 2011
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    Ah, thank you very much. My instructors are of the same opinion on 741s, but they are cheap and serve to illustrate basic concepts. We will be using others as the course progresses, which is exactly why I want to have a simple facility to test circuits at home, before entering the lab.
    Now I need something clarified, if you would:
    What if I want to play the waveform "live" and in real time out my card, not through a pre-generated .wav file ... which connection would I use (R/L)? What I mean is, can I set up the sound card to specifically send the signal to one wire only? How shall I treat the wire not in use?
     
  6. SgtWookie

    Expert

    Jul 17, 2007
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    40+ years ago, they were the greatest thing since sliced bread.

    Nowadays, they're best used as kitty toys. My cat likes to swat them around the floor. ;)

    If the "live" waveform is monaural, it should be going to both outputs. Just use the left output, and leave the right output disconnected. Don't short the L/R outputs together nor to ground, as there's a chance you could damage your sound cards' output.

    You'd really be better off to use a TL072 or TL082 opamp to buffer the sound cards' output signal, capacitively coupled. Otherwise, you risk destroying your sound card. They are not very tolerant of abuse.

    If possible, it would be preferable to use an inexpensive ISA add-on sound card rather than one that's built into your motherboard. If you zap the mobo, you have an expensive repair ahead of you. If it's an add-on card, you toss it and plug in another one after you find out what you did wrong to zap it.

    That depends on the software you're using.

    Leave it disconnected.
     
  7. daddycool

    Thread Starter New Member

    Jan 30, 2011
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    I think mine would enjoy playing with them, too. ;)

    Why is that? It sounds as if there are risks involved here.
     
  8. SgtWookie

    Expert

    Jul 17, 2007
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    The speaker/headphone out is somewhat more robust than the line out. However, you can still "zap" them. The line out is designed for a 10k Ohm load. The line in is quite sensitive; if you put in more than about 1v p-p you'll probably fry it.
     
  9. daddycool

    Thread Starter New Member

    Jan 30, 2011
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    So keeping output signal under 1Vp-p should be fine, then? I don't see myself doing much than that. Thanks.
     
  10. spinnaker

    AAC Fanatic!

    Oct 29, 2009
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    I think wookie was referring to input voltage. If yo were to accidentally attach the sound card to some place in your circuit where you are not supposed to, you could fry your Sound card. There is a very recent post on this where someone fried their sound card on their laptop.
     
  11. daddycool

    Thread Starter New Member

    Jan 30, 2011
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    Accidents...I forgot about those! Now the advice about a buffer makes good sense.
    A big thanks to beenthere and SgtWookie for your help, and to spinnaker for the clarification.
     
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