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The Atten ADS1102CA Digital Storage Oscilloscope “Hands-On” Review by Mauro Grassi. This affordable dual-channel DSO has many features found in more expensive oscilloscopes, with a wide analog bandwidth of 100MHz, a colour LCD screen and good connection options. It is light, portable and very quiet in operation. T he prices of entry-level DSOs have fallen in recent years and many have features previously found only in more expensive models. One of the most affordable in its class is the Atten ADS1102CA, a dual channel model with an analog bandwidth of 100MHz and a colour TFT LCD screen. While the higher bandwidth of this DSO makes it substantially more expensive than, say, 20-25MHz or even 50-60MHz models, it still represents very good value for the combination of software and hardware features that it has. the resolution of the screen won’t matter particularly, because you’ll be looking for qualitative features of the waveform (and any quantitative features can be measured). On the plus side, the display is bright and can be read well over a range of viewing angles. 1GS/s but this only applies if using one channel. If using two channels, you need to halve this rate (and the rate of 500MS/s applies only if the timebase is faster than 50ns per division). Each knob is “digital” and responds to turning and pressing. There are two other, smaller, knobs on the front panel. One is used to set the trigger level and Front panel layout is grouped with the buttons associated The front panel of the ADS1102CA with the triggering menus. The other is mimics other DSOs we have reviewed. a so-called “universal” knob, used to The layout of the controls is logical, change different settings depending on with buttons grouped according to the context and it lights up when it can function. be used to change a setting. There are dedicated offset and ampliThe six menu buttons are laid out in LCD screen tude (vertical scale) knobs for each of two groups of three; there is a dedicated The screen is a 64K colour (16-bit), the two analog channels, and another help button and illuminated buttons for 5.7 inch TFT LCD with a resolution pair for the horizontal timebase. The each channel. In addition, five context-sensitive of 320 x 234 pixels (close enough to timebase can be varied between 2.5ns QVGA at 320 x 240 pixels). You can and 50s per division. The real time buttons run down the right hand side vary the brightness of the LCD and its sampling rate of the ADS1102CA is of the display that correspond to the menus displayed on the intensity, as well as choosscreen. The menu system ing the look of the grid. is simple to use and apThe rendering can be in pears and disappears as vector or “dot” mode and Input channels: 2 required. It is hiearchical you can enable timed or Analog Bandwidth: DC to 100MHz and in some cases encominfinite persistence. While Sampling Rate: 1GS/s (single channel) passes more than one on the screen is big, its resoluMemory Depth: 40Kpts screen page. You move tion is relatively low – the Vertical Sensitivity: 2mV/div (at x1) from one “page” to the major compromise with next using the lowest of this model. Vertical Resolution: 8 bits the five buttons. A colour screen is conLCD Display: 5.7inch 16-bit colour TFT QVGA, The menu display dissiderably more attractive 320 x 234 pixels appears when a timeout than a monochrome display Size and Weight: 305 x 154 x 133mm; 2.3kg period expires without though and in most cases, Specifications At A Glance: 92  Silicon Chip 305mm x 154mm x133mm siliconchip.com.au user input and this can be set from two to 20 seconds (the timeout can also be disabled). There is a dedicated button, just above the five context sensitive buttons, that can be used to make the menus disappear instantly. When the menus are visible, you can still see 10 of the 12 timebase divisions of the waveform display (and always eight vertical divisions). As mentioned, some of the pushbuttons are illuminated, usually green but some change colour; the RUN/STOP button is green when running and red when stopped. Each of the two channels has an illuminated button that is lit green when the channel is enabled. Pressing this button also brings up the options for that channel. Analog input connectors There are BNC connectors for each of the two analog channels that accept (passive) probes, as well as an external trigger input. The ADS1102CA is supplied with two passive 100MHz probes Fig.1: this screen grab shows the 1kHz square wave used for probe compensation. The frequency counter is in use showing the frequency is very close to 1kHz. The voltage scale is shown as 56mV per division (on the “fine” setting) which makes the amplitude around 170mV (or 340mV peak-to-peak). Note that the ADS1102CA can also perform a self test and self calibration procedure. siliconchip.com.au with switchable x1 or x10 attenuation, although the settings allow for x10 and x1000 probes as well. The ADS1102CA has a 1kHz compensation output, for calibrating the probes. You connect the probe to the compensation output and adjust its trimmer capacitor until the “square” wave looks square (see Fig.1). Apart from the two BNC sockets for the two Fig.2: this shows the cursors being applied to a simple sinusoid. The cursors are in the time domain (horizontal axis) and you can position them anywhere on the screen using the “universal” knob. In this case we can accurately read the time difference between the two cursors as 4.12s. The cursor time positions are also shown. March 2011  93 analog channels, there is a third BNC socket for an external trigger input. Signal-coupling Pressing the channel button allows you to vary the coupling for that channel (AC, DC or GND), as well as to apply bandwidth limiting. The GND coupling simply connects the channel to a GND reference. This oscilloscope’s inputs have a fixed 1M impedance and are rated for 400V (CAT II). There is no 50 input option. Bandwidth limiting Each of the two analog channels can be bandwidth-limited to 20MHz. This is a good idea when you want to ignore very high frequencies as it reduces noise (ie, above the 20MHz cutoff frequency). If you know beforehand that your signals are below 20MHz, you should enable this. Note that although this is a 100MHz oscilloscope, this requires the probe to be used in its x10 setting. The bandwidth is only 10MHz if you use the probe in the x1 setting and so the inputs are essentially always bandwidth-limited in this case. In the menus for each channel you can also choose whether the vertical knob for each channel works in “fine” or “coarse” mode; in the latter, the knob follows the common 1-2-5 sequence while in fine mode, there are many more intermediate steps. Pressing the vertical scale button toggles between the two modes. The “fine” mode is good for using the available screen area most effectively. The offset knob, when pressed, sets the GND reference for the channel at 0V (centred vertically on the display). From there you can move it up or down as necessary to position the trace on the display. Trigger options You can trigger on an edge or pulse width, on the AC line (50Hz in Australia, New Zealand and the UK etc), or via an external input. The edge triggering can function in video, slope or the so called “alternative” mode. The latter makes the trigger alternate between the two channels, which can be very useful for stabilizing waveforms of very different frequencies. The trigger options are comprehensive, allowing you to choose the pulse width, edge polarity, to sync on odd or even video fields etc. If in doubt, you can always use the AUTO SET feature which has its own button. This sets the parameters automatically to obtain the best display. In this DSO, the AUTO SET feature can be customised so that it optimises the display for one or many cycles of a waveform. A nice feature of the AUTO SET is that it can be undone, if you decide it’s not exactly what you were hoping for. All the usual modes are available and you can display traces in XY or YT mode. The latter is the usual time on the X-axis and voltage on the Y-axis mode, while the former plots the channels against each other and Fig.3: screen grab showing the FFT (green trace) applied to a square wave (yellow trace). The FFT trace can be displayed either superimposed on the main display, or in a split screen mode (as shown here). In this shot, the frequency domain stretches over the whole analog bandwidth of 100MHz. The vertical scale is in dBVrms, decibels with respect to 1V RMS. 94  Silicon Chip is useful for seeing phase differences among other things; the display will be a Lissajous figure. Acquisition and triggering You can easily set up the triggering by using the “SET TO 50%” button. This has the effect of setting the trigger point to half of the signal amplitude. This is a good starting point for then customising the trigger condition. Noise reduction The ADS1102CA can average up to 256 waveforms in real time and display the result, reducing the effects of noise. You can also enable a digital filter which can be configured to work as a low pass, high pass, band-pass or band-reject filter, with configurable cutoff frequencies. Peak detect sampling can also be enabled, to see very fast glitches in a waveform. The peak detect mode will trigger on glitches down to a mere 10ns. MATHs functions This oscilloscope has the basic MATHs functions that would be of the greatest use: you can add, subtract and multiply two waveforms and display the result. You can also perform an FFT (Fast Fourier Transform) on a waveform and have it displayed on the screen. The FFT can work in one of four modes, each suited to a particular task: Rectangular, Hamming, Blackman and Hanning. The FFT has a 10 x digital Fig.4: all the measurements which can be displayed for a waveform, shown at once. The waveform itself will be concealed behind the measurements display but you can see all the vital statistics. When a measurement is unavailable, it is shown as a string of asterisks. The frequency counter is shown at the bottom right corner and is separate to the measurements. siliconchip.com.au zoom (in the frequency domain) and you can choose to have the FFT superimposed on the main display or appear separately in a split screen configuration. See Fig.3. Cursors There are two vertical and two horizontal cursors that can be used to measure parts of a captured waveform, with up to two cursors used on a waveform at any one time. The cursors can be applied to the MATHs waveform, as well as to a previously “stored” waveform (one of the so-called “reference” waveforms). This is useful if you wish to examine in detail a portion of a waveform. Each cursor can be positioned using the “universal” knob. It can work out the difference between the two cursors, or get the reading at that point. The back panel houses only the pass/fail out socket and RS-232 and USB ports. Mains power connects via an IEC socket under the rear. difference, time between first falling edge of first waveform and last falling edge of second waveform, etc. Automatic measurements Counter You can enable measurements on a waveform from a comprehensive set; they are displayed superimposed on the LCD, as shown in Fig.4. The following are among some of the measurements: frequency, amplitude, RMS voltage, positive pulse width, fall time, duty, overshoot, true RMS, mean voltage. When you select to display “All Measurements”, the measurements are in three groups. You can choose to enable or disable all the voltage, all the time or all the “delay” measurements. The first two are self-explanatory. The “delay” measurements include phase Although you can measure the frequency of either of the two channels, for best accuracy you can use the built in frequency counter with up to 6 significant figures of resolution. Pass/Fail mask The ADS1102CA has a simple pass/ fail feature that is very useful for testing hardware. You can define a “pass mask” and get a simple PASS/FAIL response for input waveforms (see Fig.5). If the incoming wave falls outside the mask, you can configure a PASS or FAIL response. The results are tallied and displayed. Fig.5: the PASS/FAIL feature. Given a waveform, in this case a simple sinusoid, a PASS/FAIL mask can be created (shown in blue). Subsequent waveforms can be compared against this mask. If they lie outside of the mask, you can configure the oscilloscope to produce a FAIL response. This makes repetitive testing easy. The number of pass/fail results are shown on the display. siliconchip.com.au Delayed mode If you enable the “Delay” option in the timebase menu, the display changes to a split screen, with the lower half of the screen displaying a “zoomed” are of the waveform (you reach this mode by pressing the “Hori Menu” button just below the timebase knob). You choose the zoom area (which is shown in the top half of the screen) by using the timebase knob and its smaller, offset knob to move horizontally in the time domain (see Fig.6). This can be useful for going back and forth in time from the trigger point and it allows you to see more detail of the waveform. USB host port The front panel also has a Type A USB host port that can be used to Fig.6: the delayed mode allows you to scroll back and forth and zoom in on a waveform in the time domain. Here the top half of the display shows the actual waveform, and the non blue area represents the selected portion of the waveform that is displayed in the bottom half of the display. We can see better detail of this “square” wave’s rise time. The waveform rises 4.40V within a 1us or so. March 2011  95 Serr v ice Se ceman’s man’s Log – continued from p48 This time, after everything had been plugged back in, there were no beeps and the scooter moved accordingly when the controls were operated. The lack of circuit diagrams can be a real hindrance in service work. If Dad buys another mobility scooter to fix, I hope he gets one with the same electronics as the one we’ve just repaired, otherwise I foresee more headaches. Intermittent car radio This next story is from F. W. of Airport West, Victoria, who recently locked horns with an intermittent car radio problem. Here’s his story . . . In 2001, I bought a 1988 Nissan Skyline R31 GTS special vehicle which was in a run-down state and in need of some major rebuilding. My licensed aircraft engineer background enabled me to do most of the work myself and I literally rebuilt most of the vehicle. Among other things, this involved rebuilding the engine, transmission and differential, plus the complete removal of the dashboard and instrument panel to replace a leaking heater core. The rebuild took about four months and when it was finished, the car started and ran perfectly. However, there was a puzzling fault in the vehicle’s radio. The car had the original radio/tape deck in it and the radio had intermittent reception. For example, if I started the car in the garage, the reception would perfect on both AM and FM. However, as soon as I had been driving for some time, the reception would suddenly fade away to almost nothing, sometimes with some static. Because the unit only had a tape deck and I wanted to play CDs, I decided to scrap it and fit a more modern radio with a CD player. At the same time, I was also hopeful that this would cure the reception problem. And so a new Panasonic radio/CD player with all the bells and whistles was fitted and it initially appeared to work fine. Unfortunately, as soon as the car was driven on a warm day the reception disappeared, just as it did with the old radio. The time had come to really sort this problem out! With the engine running, I checked the supply line to the radio and found this to be at about 13.5V, as expected. The earth connections were then checked and these also proved to be OK. Next, I removed and carefully inspected the roof-mounted antenna. I also checked the continuity of the antenna cable, checked for shorts between its inner core and the braid and checked the earth connection on the roof. No faults were evident. And then something strange happened. With the advent of winter, the problem suddenly disappeared and was all but forgotten until the following summer when it just as suddenly reappeared. By now it was beginning to dawn on me that the problem was temperature-related but what could it be? I would like to say that the problem was found by my years of troubleshooting expertise. However, it came down to a simple car wash to find the fault. I was at my local car wash and wanted to listen to some music from the radio while the car was being hosed. As a result, I turned the volume up so I could hear it with the windows up. As I washed around the roof-mounted antenna, the volume of the radio varied up and down dramatically. I then found that moving the antenna by just a small amount duplicated this effect so when I got home, I removed the antenna and repeated all my previous antenna checks. To my amazement, I found nothing. It was only then that I thought to look down into the hole in the roof where the antenna fitted. When I did, I noticed the end of a screw which held the central internal mirror base to the roof. This screw was too long and was within a bee’s whisker of touching the antenna base. Obviously, as the car roof heated up, it expanded just enough to allow this screw to touch the antenna’s base. I fitted a shorter screw to the mirror base and the problem was solved. The mirror was one thing that I had not removed during the rebuild so I suspect it was like that from new. SC Atten ADS1102CA Digital Storage Oscilloscope: continued from page 95 connect a USB flash drive. This allows you to store waveforms, settings and take screen grabs. You can also connect a PictBridge compatible printer directly using a Type B USB socket on the back panel. There is a dedicated button for printing screen grabs on the front panel. You set the printing mode (ink saver on/ off), layout (portrait/landscape) and paper size in the menu system. This bypasses the need for a PC to print; you can obtain a hardcopy immediately from your printer. The USB port also allows you to connect this DSO directly to a PC and use the supplied Windows software suite, EasyScope, to control the oscilloscope. The only other connectors on the 96  Silicon Chip back panel are the IEC power socket, a serial port and an additional BNC connector that is used for pass/fail testing, as described earlier. Note that the firmware can also be upgraded using a USB flash drive. Customisation options Interestingly, the waveform interpolation can be switched between sin(x)/x (commonly used and optimal for reconstructing waveforms) and linear (linear interpolation simply connects points using a straight line). There is also a comprehensive help guide in a number of languages, including Chinese, Japanese, Arabic and Russian (as well as English!) and a selection of up to four “skins” which vary the look of the display. In summary, the Atten ADS1102CA DSO is a portable, affordable DSO with many good features and is very capable. It is supplied with two switchable x1-x10 passive probes, good for 100MHz, user manual (CD), Windows EasyScope software (CD), IEC power cable and USB cable. Where from, how much? The ADS1102CA is available from from Wiltronics (www.wiltronics. com.au). It costs $A760 plus GST. Contact: Wiltronics Research Pty Ltd, Unit 4, Corner Ring Road & Sturt St, Ballarat Vic 3350. Phone (03) 5334 2513 or Free Call 1800 067 674. Email: SC sales<at>wiltronics.com.au siliconchip.com.au