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Sound Card ADCs For Electrocardiograms

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This system is useful as a way to detect a transmitting phone at close range, however due to the limited bandwidth of a computer soundcard, it is in no way capable of actually decoding the transmissions. As far as other experiments go, why not use your soundcard to detect lightning

I like inspecting the output of this circuit using my computer sound card. Probing the output pin on an oscilloscope reveals a beautiful ECG signal, but not everybody has an oscilloscope. I've seen some project webpages out there which encourage people to use the ADC of a microcontroller (usually an Arduino) to perform continuous measurements of voltage and transmit them over the USART pins, which then get transferred to a PC via a USB-to-serial USART adapter (often built around a FTDI FT-232 breakout board or similar), only to get graphed using Java software. That sequence certainly works, and if you already have an Arduino, know its sketch language, and are happy writing software in Processing, that's a great solution for you! However I found the sound card option convenient because everyone has one, and with a click-to-run computer program you can visualize your ECG right away. Note that I added a potentiometer to drop the voltage of the ECG output to make it more suitable for my microphone jack. Ideally you'll find a resistance that uses a lot of your sound card's dynamic range without clipping.

The SoundCardECG project on GitHub is a click-to-run Windows program I wrote to display and analyze ECG signals coming into the computer sound card. The screenshot above shows my heart rate as I watched a promotional video for a documentary about free-climbing. You can see where my heart-rate elevated for a couple minutes in the middle as I watched a guy free-climb a cliff a thousand feet in the air without safety gear. This software is written in C# and fully open source. It certainly works, but has many avenues for improvement (such as enhanced QRS detection). Interactive graphing is provided by the ScottPlot library.

I built this AD8232 breakout board into a nice enclosure to make it easier to experiment with it in the future. The circuity isn't anything special: a linear voltage regulator with capacitive decoupling on the input and output, and an op-amp serving as a unity gain amplifier to buffer the output accessible through a SMA connector, and a current-limited output attached to a female 1/8" audio for easy connection to my computer sound card.

Using a sound card as a scope is not a new idea. After all, a sound card is nothing more than an ADC with a sampling rate of about 100,000 samples per second or 100 kS/s, with typically 16-bit resolution.

Even before you connect a sound card to the external world, you can explore the scope features using the built-in sound card in your computer, with its built-in microphone as input and speakers as output.

Your sound card is taking data at a fixed rate; usually about 96 kS/sec and with a fixed full-scale voltage range at 16-bit resolution. It is fixed. The vertical and horizontal controls of the scope are just changing the display of these measurements.

The limitations of using a sound card scope are due to the performance of your sound card. There is a limit to the lowest frequency and highest frequency that can be measured and to the highest voltage and lowest voltage.

To reduce this risk, I strongly recommend when you want to connect an external signal from one of your projects, do not use your internal sound card. Instead, purchase a low cost external USB sound card.

For example, the Sabrent ( -MMSA/usb-external-stereo-3d-sound-adapter-black/#description) low cost ($8) USB sound card has an internal 16-bit ADC that can sample up to 196 kS/sec, but has a limited input frequency range from about 100 Hz to 20 kHz. The Waveforms software tool can drive this USB sound card.

To connect the real world to a sound card, I used a common audio stereo cable plugged into the sound card and a microphone socket


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