DIY sound card oscilloscope for $ 1

There are a lot of projects for creating oscilloscopes from various kinds of audio cards. Modifying a card in order to turn it into a tool useful for an electronic engineer is not so difficult, but often the price question arises. And here an interesting option comes to the rescue with a question price of about $ 1.

Exactly how much is an external sound card, which is shown in the announcement photo. You can buy this miracle of technology at an electronic flea market (in many cities there are such), or at an online auction, where there is always something to choose from. The marking of the current device is HX2010-0705, it was released at the end of 2013.





The device is hybrid, it is a sound card + HID input. As for the latter, this part is designed to adjust the volume and perform some other tasks, including working with media keyboard.

USB descriptor dump: Apparently, the chip inside is similar to the chip installed in low-cost C-Media sound cards, without any buttons. Notes:

VID=0x0D8C PID=0x000C
Product string: C-Media USB Headphone Set
Audio Device Class + HID (composite device)


• the audio input is mono, and two contacts should not be misleading, they are closed to each other; The DLL is generic here, it can work with both stereo cards and mono. The second channel can be disabled independently.

• Sampling frequency - 44100 and 48000 Hz;
• 2.23 V at C6; short circuit current of 20 mA, with the addition of a resistor of 120 k, this indicator can be reduced to 8 mA;
• A 120k resistor is the most inexpensive method of increasing the measuring range to 0-6V;
• AGC needs to be removed, the settings should be as follows:

Capacitor C6 needs to be soldered, its capacitance is 80 nF, and it can seriously limit the capabilities of our oscilloscope.

Settings:


Calibration is best done using the appropriate function in the GUI. Here is an example of the work of what happened as a result:







Software for work:

• dsoundscope.dll + miniscope v4 (binaries)
• dsoundscope.dll (source)
• miniscope v4 GUI
• miniscope v2d STM32F3 PC / USB oscilloscope with an arbitrary waveform generator, which was used for testing.