Experimenting with virtual instrumentation

13 August 2014

LabKit, the new product in the openDAQ store, offers users the possibility to perform their own electronic projects, at home or anywhere, with a very reduced spending of money on instrumentation.

The kit has two audio jack connectors, which are designed to be plugged to the inputs and outputs of the multimedia Sound-Card available in almost every modern PC. 

One of the connectors may be used to get a voltage from the headphone output of the sound card, while the other jack plug may be used to set connection between the breadboard and the line input of the sound card. 

The multimedia audio hardware of a standard PC offers much under-utilized potential for scientific and amateur projects. A conventional PC soundcard includes, among other things, an analog to digital converter (ADC), for converting external sound signals to digital bits, and a digital to analog converter (DAC) for converting digital bits back to sound signals. Generally, both are two-channel (stereo), offer 16 bit resolution, and a sample rate up to 44.1kHz. Commonly, the APIs from the Operating Systems offer straight access to these features, which allows reusing the hardware of the sound cards for other purposes.

There are many applications from third party developers, which can be directly downloaded from Internet, and that allow using your sound card as an oscilloscope, a signal generator or even a frequency response analyzer.

In any case, be aware that it is not advisable to use oscilloscopes based on the sound card, because they have an AC filter on its inputs: The sound cards are designed to work with signals into the audible sounds frequency range (0.2-20kHz), and they have filters that eliminate any other frequencies. The greatest disadvantage is that any DC component of the voltage inputs won’t be displayed.

E.g.: Generatosaur is a free software utility that turns your sound card into a low-frequency tone generator. The program generates different low frequency signals, and lets you choose amplitude, frequency and waveform for left and right channels separately.

Another very interesting option, are the aplets developed by by PhD W.A. Steer (http://www.techmind.org/audio/index.html). These applets include several separated sound-card  based instruments, like a spectrum analyzer, a frequency counter, and a signal generator:

If you are interested on digital signal processing, BasicDSP is a good option. BasicDSP is an educational software that makes it easy experimenting with simple Digital Signal Processing algorithms for audio signals. The input can either be taken from the sound card, or be a locally generated sine wave, white noise or impulse signal. The output is fed to the sound card, as well as to a virtual oscilloscope and spectrum analyzer. 

 

PC based oscilloscopes

OpenDAQ is a very versatile instrument for adquiring many kinds of signals, but it has its most significant limitation on its bandwidth. If you need to test your circuit with a faster instrument, an oscilloscope, there are some interesting, and not very expensive, PC based options. They use a minimum external hardware (usually, using USB connection), and a PC based software, to offer solutions with a performance not very different from the regular laboratory instrumentation. 

The openDAQ's LabKIT connection board has two BNC sockets that can be used to connect directly (using a BNC-BNC cable) to these PC based instruments, or even also to conventional laboratory oscilloscopes and signal wave generators.

For those needing only a basic device, an interesting option is the Educational PC Oscilloscope Kit from Velleman [EDU09].It costs less than €40 and has a bandwidth from DC to 200KHz, and an input range from 100mV to 5V/Div: 

If you need a better oscilloscope, Picotech has a good variety. One of the Picoscope 2000 series can be an excellent option:

 

Another company, Virtins has an even wider variety of oscilloscopes and other lab instruments.