PC USB Oscilloscope Tutorial

- using a personal computer, PC to provide much of the processing and display for a digital oscilloscope is a great way to reduce costs while being able to gain the best performance for a given cost. USB scopes have become the standard method of achieving this as a result of its widespread use.

USB oscilloscopes using the power of a PC, personal computer, have become a very popular way of buying a relatively high performance oscilloscope for a low cost.

The PC USB scope utilises the processing power, display and often gains power from the PC. In this way it is able to utilise widespread low cost items to perform many of the functions of the scope, and considerably reduce the cost for a given level of performance.

Why USB for digital scopes

It is possible for scopes using personal computers, PCs, to use a variety of methods to link to PCs. However in recent years USB has become standard on virtually all computers and as a result it does not require the use of an additional card like a Firewire card, etc to use one of these oscilloscopes.

Using USB means that it is possible to use a scope using the PC processing power on virtually any PC.

The other advantage is that having a digital USB scope design enables the advantages and cost savings of quantity can be made. Fewer variants are required for different interfaces, and therefore it is possible to focus on optimising the design for USB.

PC USB scope basics

One of the key elements of the PC oscilloscope is naturally the USB link. This provides a convenient and sufficiently high speed data link by which the USB scope and computer can communicate.


Note on USB, Universal Serial Bus:

The USB or Universal Serial Bus Interface is a well-established interface for computer communications. Combining speed and simplicity, this robust interface is available on most computers and is used for connecting many peripherals from cameras and mobile phones to test instruments and many other items to computers.

Click on the link for further information about Universal Serial Bus, USB


Although the oscilloscopes from different manufacturers will differ, and USB scopes providing different levels of functionality will naturally be different, there are some common aspects of these scopes that can be outlined.

The PC USB scope architecture, as would be expected, has many similarities to that of a standard digital oscilloscope. It is just that a portion of the functionality is contained within the PC.

When the signals enter the scope they enter an analogue section where they are pre-conditioned by amplifying them, attenuating them or adding a DC offset as required. This ensures that the signals are within the required range for the further stages.

The next stage is where the signals are converted into a digital format by analogue-to-digital converters. The sample logic circuitry controls the sampling process and the subsequent storage of the data in a memory area called the capture memory.

Like other digital scopes, the USB versions also include triggers which control the start and end of the samples. Additionally internal controller sets signal gain levels and offset, as well as controlling the sample logic, selecting trigger source, trigger level, and trigger polarity, and communicating with the PC.

PC USB scope advantages / disadvantages

There are many advantages and disadvantages to using a PC based USB oscilloscope. These need to be balanced when deciding whether to use or buy one of these test instruments.

Advantages

  • Cost effective:   One of the big advantages of using a USB oscilloscope is that it is a very cost effective way of buying an oscilloscope. The overall instrument utilises many aspects of a computer that is likely to be available already. Power supply, display and processing power are all available within the PC and this means these do not need to be replicated within the USB scope.
  • Easy to set-up and use :   Using a USB interface means that connecting the PC and the scope together is particularly easy. It is a well tried and tested interface that is simple to set up. Normally the software used with the scope is also designed to be very easy to implement.
  • Large screen:   Most PCs, whether a laptop or desktop have a good sized screen, making the waveform images easy to see.
  • Utilises existing equipment :   USB oscilloscopes utilise PCs which are likely to be already available. This means that it is unlikely that it will be necessary to buy a new one particularly for that role.
  • Portable :   The USB oscilloscopes are very much smaller than dedicated oscilloscopes. For field service, many engineers will already carry a laptop, so the fact that the USB scope is much smaller than a dedicated oscilloscope provides a real advantage.

Disadvantages

  • Performance:   While the performance that can be attained by PC based oscilloscopes is improving all the time, and is surprisingly high, they tend not to compete with the very high performance self-contained scopes that are available.
  • Requires a PC:   The fact that a USB scope requires a PC can be an advantage in some instances, but in others it can be a disadvantage is one is not already available.

By Ian Poole


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