How to Use Your Sound Card as an Oscilloscope

An expensive piece of test equipment used to analyze and graph the waveforms of electric signals (AC and DC), an oscilloscope may be out of the price range of most hobbyists. Though certainly not as good as the real thing, you can simulate an oscilloscope with the sound card on your PC.

Instructions

Difficulty: Moderately Challenging

Things You’ll Need:

• Sound card
• PC
• Sound card oscilloscope software
• Old headphone cable (1/8 in. jack)
• Soldering iron
• Solid core wire

1. Download PC sound card oscilloscope software. Some of the more commonly used software includes Zelscope, Audiotester and Scope, which can all be downloaded at little or no charge to the user (see Resources below).
2. Configure your PC to record sound via the microphone or line in port. Though you may not actually be recording any of the signals you'll be capturing, the PC sound card oscilloscope software uses the same interface used to record sound. Double-click on the volume icon in the system tray and be sure both the Line Volume and Microphone Volume levels are turned up and not muted.
3. Make a set of probes. This requires an old headphone cable with an 1/8 inch phono jack, a soldering iron and some solid core wire. Cut off a long section of the wire and strip the ends opposite of the phono jack. There should be three wires if the phono jack is stereo, only two if the phono jack is mono.
4. Solder solid core wire to the ends of each wire. Solid core wire can be plugged directly into breadboards or used as probes. If you desire, you could solder banana clips, alligator clips or any type of connector or probe to the ends of the wires.
5. Make a voltage divider. A voltage divider is required because your sound card was intended to be used with low-power audio devices. The maximum voltage from your circuit should be around 1.7v. The sound card should be protected against some voltage spikes, but anything above 5v may permanently damage your sound card. A voltage divider can be created with resistors or a potentiometer.
6. Test the voltage divider. Since the voltage divider may be the only thing protecting your sound card from the higher-voltage circuit, supply a DC voltage of the maximum voltage your circuit can output. Measure the output of the voltage divider. Remember, you're aiming for an output voltage peaking at 1.7v or lower.
7. Start the PC oscilloscope software. Once started, you will see an oscilloscope-like interface. You may also want to turn down the volume of your speakers as many waveforms can sound very loud or even damage your speakers.
8. Test your circuit with the probes. Though you won't be able to probe the circuit as freely as you would with a real oscilloscope, you will at least be able to get some information about what's happening in your circuit.

Tips & Warnings

• Voltages in excess of 1.7v can potentially damage your sound card. Be sure you test the voltage divider before probing the circuit!

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