Digital Storage Oscilloscope (DSO) is an indispensable tool to analyze complex signals or debug electronic devices. Because the signals are sampled and stored into memory it is very easy to examine them and their relations. DSO is in fact a special computer with many fast A/D converters and software to analyze and display signals. With DSO the problem of displaying short-time signals and glitches is history. It only depends on your settings and trigger conditions to capture the right moment. Storage capacity is rarely problem unless you would like to store longer intervals.
Because of the computer-based design of the DSO it is pretty simple to convert ordinary PC into a DSO. PC Based digital storage oscilloscope is in fact software which runs on a PC with suitable interface for analog signals. This interface is usually a small box with fast A/D converters connected to the parallel or USB port. PC based oscilloscopes have many advantages over classical DSOs. Since the capabilities of the software are limited only by the interface and computer resources it is possible to track many channels in real time, analyze FFT spectrum or decode buses like SPI, I2C, JTAG or UART.
The physical limitations of a PC oscilloscope are mainly defined by the external hardware that is used to sample analog or digital signals. The main parameters that define PC DSO capabilities are number of channels, bandwidth, sample rate and sample memory size. The sampled data is stored into buffer from where it is transferred to the PC where it is analyzed and displayed. Therefore, at least in principle the buffer needs only to be large enough to store samples until they are transferred to the PC. Only in principle because the parallel port is not fast enough to transfer huge amounts of data in real time.
A big advantage of PC based oscilloscopes is upgradeability of the software. You simply install new version and you get bugs fixed or new functionality. Some PC oscilloscopes also allow you to write your own plugins for custom decoding. The average price of PC oscilloscope is significantly lower than the price of a real DSO but it is still higher than the price of the PC where it will run. Nevertheless, PC DSO is a compact, cheap and universal solution for hobby or professional electronics laboratory. It allows you to analyze arbitrary signals, to decode popular serial protocols and to store signals for later processing.
A special version of PC based oscilloscope is the I2C analyzer. This is a simplified device which samples few channels and decodes I2C, SPI, UART and other popular protocols. An important function is the I2C host adapter mode which allows you to send I2C or SPI packets and act as a master device.
I2C analyzers are much cheaper then PC based DSOs and many such devices can also be used as a logic analyzer with basic functionality.
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