CleverScopeCS328AUSB dual channel100MHz mixedsignal oscilloscopeHooked up to a desktop or laptop computer, this USB oscilloscope andits supplied PC software provide a large range of functions, includingdata logging. With the optional signal generator you can also testaudio equipment, measure THD and do frequency sweeps.CLEVERSCOPE is the New Zealand-based companybehind the CS328A, a dual channel 100MHzmixed signal USB oscilloscope with two analogand eight digital input channels. With optionalaccessories two units can be linked to double that numberof channels.20mV/div to 20V/div (using a x1 probe). The vertical resolution of the digitising system is 10 bits for the basic modeland you can increase this to 12 or 14 bits by purchasing anadditional sampler board.Unlike some USB oscilloscopes, this one has a deepmemory of 4Mpts (Million Points) for the basic model.Main specificationsFront and rear panel connectionsThe CleverScope CS328A provides two analog channelsThe front panel of the CS328A comprises three BNCand eight digital channels (the corresponding analog only connectors (two for the analog channels and one for themodel is the CS320A). Its analog bandwidth is 100MHz external trigger), two RJ45 sockets (for connecting the eight(measured at the -3dB point), while the digital sampling digital inputs), two probe compensation terminals and tworate is 100MS/s (millions of samples per second). There LEDs, green for power and red to indicate triggering.is a hardware 25MHz anti-aliasing filterOn the back, there is the USB port, afor better spectrum analysis.BNC connector for the signal generatorThe vertical sensitivity ranges from Review by Mauro Grassi output and the power input jack and10 Silicon Chipsiliconchip.com.auAt left: the CS328A along with its two analog and two digital“probes”. On the laptop screen is the supplied PC software usedto control the USB ’scope. A sinusoidal wave is shown in thescope graph window while smaller windows are shown aroundit. All controls stem from the control panel shown at top right.Windows can be shown or hidden from the control panel.an RS422 port.The optional RS422 link cable forms a 100 Mbit/s communication link between the two. When you connect thetwo CleverScope CS328As together in this way, you effectively have a four channel analog scope with 16 digitalinputs and a single user interface.Probes and accessoriesThe CS328A is supplied with two switchable (x1, x10)100MHz analog probes. Also included are adaptors thatconnect to the two front panel RJ45 jacks allowing you toconnect up to eight (two lots of 4) digital inputs.The CS328A is controlled using the supplied PC software for Windows. The software is controlled from themain window and secondary windows become visible asneeded. Like other oscilloscopes, the CS328A has an “AutoSet” button, which will analyse the signals and choosethe vertical and timebase settings for displaying them onyour PC screen.The signal window also has small buttons, whose function is selected by hovering over them with a mouse. Theseallow you to either zoom in or out or scale the window tofit the signal.Triggering and acquisition modesEach analog channel can be AC or DC-coupled and thetriggering supports high and low frequency rejection forgreater noise immunity. Although this oscilloscope hasan operating bandwidth of 100MHz, as is usual with anywideband digital it is often better to limit the bandwidthto get a better display – with less noise. In this case youFig.1: the scope graph window showing the digitalchannels. The triggering is set to a rising edge on digitalchannel 1. A low frequency square wave is shown, withthe decoded logic values. The voltage threshold for thelogic decoding can be defined.siliconchip.com.auSpecifications at a glance:Analog input channels: ....2Digital input channels:...... 8Analog bandwidth:............DC to 100MHzSampling rate:..................100MS/s simultaneous on both channelsMemory depth:.................4Mpts.........................................(8Mpts withoptional memory upgrade)Vertical sensitivity: ...........20mV/divVertical resolution: ...........10, 12* or14 bits*Size:..................................153 x 195x 35mm (*depends on optional module)can switch to 20MHz band limiting.Triggering on a preset pattern on the digital channels isalso possible.To do this, you select a state for each of theeight digital channels. The signals must match thepattern for the trigger to occur. For example, you can trigger on a rising or falling edge, or an absolute highor low level of for that channel.There are two trigger sources. The primary one is an edgetrigger., while the secondary trigger allows you to select thenumber of times that the primary trigger must occur for thesecondary trigger to be flagged, among other modes. Youcan then select the trigger source among either.The acquisition modes include peak detect (for capturing fast glitches) and repetitive waveform modes. Thelatter mode works by assuming that the signal is periodicand filling in subsequent cycles. This mode substantiallyincreases the resolution of periodic waveforms which maybe important for high frequency signals.Optional signal generatorAlthough it is not installed as standard, the CS328A canbe enhanced with a signal generator module. This worksat up to 10MHz and you can select sine, triangular andsquare wave modes. You can also select a sweep modeFig.2: a relatively high frequency triangular waveshown on the scope graph using the repetitive waveformacquisition mode. The triangular wave is at a frequencyaround 2MHz and was generated using the optional signalgenerator module of the CS328A.October 2008 11Fig.3: the maths equation builder window. We haveselected to apply the equation X2-X3 to a sinusoidal wave.The result is shown in the maths graph window. The mathsgraph window is a separate window that can display up toeight user-defined maths traces.Fig.4: the Fourier Transform window is shown. The inputis a low frequency waveform at around 20kHz. The smallwindow at the top left corner inside the spectrum graphwindow shows information about the signals. You canchoose a log plot rather than a linear one too.which allows you to measure the frequency response of afilter, for example.seen in a separate “Signal Info” window.The range of available measurements includes theRMS and peak-to-peak voltage, as well as maximumand minimum levels. The THD of the signal can also bemeasured; very useful for audio work.Equation builder and signal analysisThe MATHs functions of the software are quite powerful.It lets you define up to eight different expressions whichare displayed in a separate window. Apart from the usualarithmetic functions, you can use functions to build upmore complex expressions. For example, you can usetrigonometric functions and integration.Many different modes for the Fourier Transform areimplemented and can be displayed in a separate window.There is also a power spectrum mode for the FourierTransform. This lets you see the power of your signal interms of the equivalent power of a periodic signal at thesignal’s fundamental frequency (ie, the first harmonic).The software allows you to view information about theanalog channels in a separate window. The fundamentalfrequency as well as the vital statistics of the signal can beExporting dataUsing the CS328A to acquire information about a signalis easy, since the control software is already running onyour PC. You can copy and paste graph and data tables toother applications. This is especially useful for writingreports and presentations. You can also export data filesfrom the logging window to embed in your spreadsheet.The software settings can be made permanent, usefulfor classrooms because the settings for a lesson can bepreloaded and will be available when the students firststart using the oscilloscope. You can also control the oscilloscope remotely using a LAN connection on your PC, formore advanced applications.Front and rearpanels (top andbottom, respectively) of theCleverScopeCS328A USBOscilloscope.The two RJ45sockets at left ofthe front panelare for the digitalinputs; the “ChanA” and “ChanB” at right arethe analog. USBconnection is viathe socket on therear panel, alongwith RS422 link,signal generatorand power.12 Silicon Chipsiliconchip.com.auFig.5: the signal information window, with expandedcontrols for data logging. This shows logging of theminimum and maximum voltage levels of the inputsignal. The logging rate of 10Hz is shown, as well as theinstantaneous vital statistics of the analog channels.Other optional accessoriesThe CS328A can be enhanced with other optional modules. Firstly, you can improve the vertical resolution from10 bits to 12 and 14 bits using optional sampler boards. Youcan also purchase a 5ns delay line to double the samplingrate to 200MS/s by using both channels simultaneouslyfor the same signal.Although the memory depth is large for a USB oscilloscope at 4Mpts, you can even double that by adding extramemory. And you can also buy more exotic probes thanthe ones supplied, including fully isolated probes (handyfor high voltage work) as well as current sensing and differential probes.ConclusionThe idea behind USB oscilloscopes makes economicsense, cutting costs by avoiding duplication, especially inthe display, buttons and knobs.Much of the data analysis can also be left to the power ofyour PC, avoiding the need for a powerful DSP or processor. The storage capacity of a common PC far exceeds theamount of non-volatile memory in standalone oscilloscopesand the PC can itself be upgraded in the future.USB oscilloscopes are therefore a very good idea forentry-level use because they are much more affordablethan stand-alone ones. Clearly, you lose the portabilityof a standalone unit that may be crucial if working in thefield. However, with laptops becoming ubiquitous andalmost feather-weight, this disadvantage is fast fading intoirrelevance.As USB oscilloscopes go, this one is a winner. Its bestfeatures include its deep memory, its relatively high bandwidth and the many features of the included PC software,which is comprehensive.The CS328A is available in Australia from Grantronics,Phone (02) 9896 7150; web www.grantronics.com.au Theprice is $1590 plus GST. In New Zealand, it is availablefrom CleverScope Ltd, Epsom, Auckland. Phone (09) 5247456. www.cleverscope.comSCsiliconchip.com.auOctober 2008 13