Picoscope 2208B Review

September 2, 2016 | 08:00

Pico Technology’s 2000 series USB oscilloscopes have a fine “bandwidth” both in terms of “megahertz” and cost: from the £99 10 MHz entry-level 2204A with 8 kS (kilosamples) memory and 100 MS/s sample rate, right up to the 2208B which at £909 ex VAT brings 128 MS depth and 1 GS/s sample rate. Not forgetting MSO functionality.

Pico have done a fine job by giving the little “Configure Your Scope” tool a prominent place on the 2000 series product page. Spartan as it may appear, the tool will prove very helpful if you have your requirements ready, and of course the amount of money to invest in your new USB scope. How many channels (2 or 4)?; what bandwidth (10/25/50/70/100)?; Probes included (yes/no)?; MSO or no MSO?

Four channels are only available on the MSO-less models, so the choice is either 2 channels MSO, or 4 channels. This choice is not available though on the entry level 2204A, which is invariably 2 channels.
This review covers the top model in the series, the 2208B MSO. Out of the box it offers:
A digital oscilloscope with 100 MHz bandwidth

8-bit resolution (sampling @ 1 Gs/s);
a spectrum analyzer;
a function generator;
an arbitrary waveform generator;
a protocol decoder;
a 16 channel logic analyzer.

This mini ‘scope is 130 x 90 x 20 mm and weighs about the same as two regulator tubes from a Tektronix 500 series oscilloscope. The color is now a very dark blue, and that’s a marked difference from the light blue casings seen on earlier Picoscopes, say the 3000 series, and we no longer have the rubber "bumpers" around two sides of the case. Also, the connectors are on the long side of the case. The 2200 series are truly compact instruments compared to the other models.

Unboxing

Rather than going for the highest sample or megahertz per buck as seen on many competing products, Pico Technology maintain a steady accent on product reliability and quality. That’s instantly obvious when I unpacked the box. This may the lowest-cost series of their USB scopes, but it is in no way inferior to the ‘pro’ products we all dream of having in our lab one day. The 2208B MSO scope proper comes with two type TA132 probes, a USB cable, a 20-way IDC-to-labeled-pins cable, 20 clip-on hooks, a quick start guide and a CD-ROM.

Getting started

As with most USB devices of the intelligent variety, you have to install the product software on your PC before connecting the device to free USB port. I chose to ignore Pico’s advice to install an approved version of the software from CD-ROM and instead went for PicoScope Beta 6.12.2.1871 dated May 10 2016, from their website. All oscilloscopes in the 2200 series employ the same software and simply enable or disable features as determined by their hardware. And that software is absolutely free, it even runs a kind of demo mode if you do not have the associated ‘scope!

The software installation went smoothly on my Lenovo U410 Ideapad ultrabook-style laptop. For connoisseurs: that’s an Intel i7 core laptop with 24 GB SSD and 1 TB HD, running Windows 7 Home Premium (no 10 for me thank you).

When connected to the PC’s USB port the 2208B MSO powers up and makes itself known with a light, rapid series of clicks from what I guess are reed relays in the box, passing a reset & verification procedure. The same little music is heard when you press the Auto Setup button in the control display to enable the scope to figure out a set of initial, global, get-u-going, setting to best display your waveform. I admit to having used that Auto Setup button a lot when I was confused with my beginner’s settings to grapple with complex signals, especially the trigger and delay stuff. It’s a much advanced version of pressing Beam Find on a ‘scope some 60 years older than the Pico.

Coming from the CRT era I was delighted to read in the Getting Started manual that your first test on the up and running Picoscope should be to touch the probe tip and view the 50 Hz (or 60 Hz) waveform known as “hum”! Hey presto:

picoscope 2208B

Notice the uncluttered screen with maximum size given to the measured signal. There’s lessons to be learned there, Microsoft people!

The probes

Again coming from the CRT era I was delighted to see Pico give a fair share of attention to the matter of The Probes. These are so underrated in this day and age with all that plug & play and digital error correction around they warrant a short discussion. My 2208B DSO came with two TA132 probes. Depending on the USB scope type, Pico supply a pair of TA131, TA132, TA159 or TA160 probes. Here, I was confused. Reading the specs table found in the probe package, initially I was unable to find any difference between the four TA’s except the rise time in the x10 position. Unless there are typos in the table, the TA160 is exactly the same as the TA131, and the TA132, the same as the TA159. Electrically, that is.

As an exercise in working with the USB scope or indeed any oscilloscope I would recommend doing the Frequency Compensation Adjustment.

I used the 2208B MSO's internal Signal Generator set to 1 kHz squarewave, 1 Vpp, to drive Channel A. The BNC-to-probe tip adapter included in the probe kit allows you to connect directly to the AWG output on the 2208B MSO. Okay, waveform appears but is not stable. Click on Auto Setup. Then select: Auto from the Trigger menu and the signal is steady. I found both probes exhibiting “overshoot” of the rising edges and wanting capacitive compensation:

picoscope 2208B

Assuming the rectangle signal from the SG is free from issues, the displayed waveform is easy to correct by adjusting a yellow screw in the probe body, using the plastic trimmer tool from the probe kit. From my experience with oscilloscopes this procedure is either forgotten, neglected, or ignored, always resulting in frustration with users chasing “strange” signals using their “gigasamples” scopes when in fact all is well and their probe is a fraction of a pF off the ideal match to the scope input.

The software through its Custom Probes menu allows exact capacitive matching to be established with non-Pico probes too, so no excuses for undershoot or overshoot -- get it right!

AWG

The arbitrary waveform generator (AWG) incorporated in the 2208B MSO is a delightful tool to use. In my case, I used it to “build” a copy of a very troublesome and at the same time volatile signal in one of my repair projects. This “playing hard to get” signal with its sudden spikes on the falling slope I was able to draw almost free-style using the Picoscope AWG software. Once saved and named "nasty" I made the 2208B’s AWG output feed the spike-infested signal to a prototype construction of the circuit on repair (okay, okay, it was a Tektronix tubed HV oscillator, self-oscilalting and producing –1600 volts). Further analysis revealed a faulty capacitor in the (low-voltage) frequency control loop, and a triode tube suffering fom grid leakage. Fixed. Thanks Pico!

MSO and Serial Decoder

So far I have failed to grasp how the term MSO for “mixed signal oscilloscope” came about. An MSO they say is the combination of a digital oscilloscope and a logic analyzer. Why the signal formats are said to be ‘mixed’ is beyond me. Is it hybrid, i.e. analog/digital? For sure, there was a time when even an analog CRT scope was able to display, say, 8 traces of digital serial signals — not too fast of course, and assuming the CRT has sufficient write speed.The 2208B MSO has a powerful 16-channel logic analyzer, which I was unable to test for this quick review, but should be beyond reproach given Pico’s reputation. A total of 20 probe clips of the hook-on type are supplied, 16 red ones (data) and 4 black (ground). These connect to a 20-way cable terminated with a polarized IDC connector to link to the 2208B MSO instrument. Wires in the cable are numbered D0-D15 and GND (4x) for correlation to the 16 traces that appear in the signal window.

Conclusion

Many stories have been written on the pros and cons of USB oscilloscopes as opposed to their stand-alone counterparts with either a CRT (now old hat) or an LCD or LED display. I will not add to the discussion other than saying that a USB oscilloscope is a great choice if you are not bothered by the constant presence of a computer on your workbench. But then, just about any laptop you have is likely to have a much bigger viewing area and higher resolution than a typical benchtop scope. Also, with a USB oscilloscope you have instant access to the waveforms appearing on the screen — no file exporting or storage media like USB sticks required.

Using the scope and the built in AWG it took me one afternoon to pinpoint and document a bad fault in a Sony audio amplifier. I realize that a digital scope, an arbitrary wave generator and a laptop PC is overkill for a basic signal tracing operation but the fact that everything is connected and instantly accessible right up to the Sony schematic on the Internet does have its advantages over wielding many separate instruments.

Although unable to exploit all features of the Picoscope 2208B MSO in this quick review, using the instrument has been an absolute delight. It has a steep learning curve and is tolerant of setting errors, with the Auto Setup function always available to get you out of a pickle. A few points bothered me though, but these are related to using a USB scope in general rather than this fine specimen from St. Neotts, Cambs. First, you need to be duly aware of the ±20 V spec on the instrument's inputs, that’s much lower than on most benchtop scopes. I know, the probes are rated 600 V DC but still. Also, I’d recommend using a dedicated PC or laptop for use in your workspace only. These things can be picked up cheaply and shpoid reduce input overload anxiety to some extent. Pico has no hassles with their scope software being migrated to another computer, licenses running out, or hard disks crashing. No such thing -- the software is free and updatable anywhere, anytime, free.

I was happy to see that the PicoScope is not a black box in the worst sense of the word. Okay it’s not open source or anything but the drivers and software development kit supplied allow you to write your own software or interface to popular third-party software packages such as LabVIEW.

Finally, as a suggestion from a self-educated repairman, can we have an audio listen-in feature added? Should be easy using USB and the computer’s sound card.

A selection of 2200 series PicoScope is available from [Interworld Electronics & Computer Industries Inc.]