Picoscope 2205A Oscilloscope - Review

Table of contents

RoadTest: Picoscope 2205A Oscilloscope

Author: terrydark

Creation date: 7 May 2014

Evaluation Type: Independent Products

Did you receive all parts the manufacturer stated would be included in the package?: True

What other parts do you consider comparable to this product?:

What were the biggest problems encountered?: Using the screen UI after using a normal CRO was uncomfortable and distracting. Using a mouse instead of interacting with knobs and switches was a big jump. Getting used to the "noise" which is often hidden my older CRO units.

Detailed Review:

Pico 2205A USB PC Based Oscilloscope

RoadTest for Element14

Overview

This is a review of the Pico 2205A USB PC Based Oscilloscope. We will look at the condition of the scope on delivery, the package contents, documentation, the scope and it’s accessories, specifications and do some measurements that I can do with equipment at hand.

My story

The offer of this device came at an opportune time for me as I had just lost an old friend, a HP1740A CRO that was destroyed by lightning.  I am currently working on a project based on an Atmel SAMA5D34 and I found myself needing a CRO or DSO to help with debugging some issues due to signal transmission over long distance.

I think this device, from Pico, will fit in well with my work area which has little room available and I often find myself working in the living space of the house and one less bulky box on the kitchen table would be very appreciated by my wife. Now don’t get me wrong, Jenny has been extremely tolerant and I probably don’t deserve her understanding because I push the limits sometimes.  Jenny does not want an electronics workshop in her kitchen. I don’t really know why ;-)

When I pack things up, there is still a pile of my work and, or at least till recent days, a huge box which was my CRO and my tools. The tools could go into a toolbox, the project into a box or an empty spot on the shelf, laptop back in the office but the CRO just sat there and was so big and heavy, it was beyond me to move with my arthritis.

The Pico was like a gift from heaven, so thank you Element14 and Pico Technology for the chance to review this very appreciated piece of equipment.

Receiving the Oscilloscope

Waiting for the Pico to arrive was torture but it eventually came. I did not realise how often I used an oscilloscope. We were not home when it did arrive and I was pretty angry as the courier had just left it at our door step. This was not usual practice. Normally the parcel would have been taken back to a depot and a note left for the recipient asking for them to pick up the parcel.  I complained but I doubt the complaint got any further than the person who answered the phone.

Unboxing

Anyway, I now have the precious item sitting on my table just waiting to be “torn open”. Waiting to be plugged in and experimented with and eventually used for its destined purpose.

Then I remembered the road test and I slipped back into reality. 

The Package

A rather ordinary looking brown box sat in the middle of my table. Well, they didn’t waste money on “pretty”. I opened the box and found the blue plastic encased device which had three sockets on the “front” and a USB “B” socket on the “back”.

Contents check

On opening the package I found the following items:

1 x Pico 2205A USB DSO/AWG device

2 x probes (x1 and x10)

Quick Start Guide

Software CD

USB lead (Type A plug to Type B plug)

Software installation

I installed the software without any problems and the Pico scope was detected. The software detected a newer version was available so I decided to proceed with this as I assumed any bug fixes and new features would be provided by the version on their site.

Quick check on some signals

A quick connect to the output of a AC transformer with auto trigger showed a typical waveform from one of these. Fairly consistent with my memory of my earlier CRO but displaying a lot more of what looked like noise than I initially expected but I realised that this is a digital oscilloscope with a digital display.  That means discrete points captured by an analog to digital converter and then subsequently displayed in discrete points in pixels. 

  There is no “fuzzing” or averaging of these noisy points as there would be on a cathode ray oscilloscope (CRO).  CROs are notorious for blurring the actual signal and then there is persistence of vision (POV). POV is the effect that allows us to watch TV or movies and interpret the images flashing at us at various rates as a continuous scene. Add phosphor glare and the “antialiasing” all this brings and you have smooth waveforms with nice slopes on curves instead of abrupt steps in vertical levels.

Digital oscilloscopes do not normally exhibit the “old fashioned” attributes unless the software is designed to do it.  What looks like poor quality display of a signal is actually a more true representation of the signal at the resolution provided by the analog to digital converter(s) in the unit.

Figure below shows greatly magnified stepped curve – no antialiasing is applied and the “jaggies” are very apparent !

Antialiasing is a technique of varying the pixels rendering to give an appearance of soft smooth curves.  It is used heavily in computer graphics ie presentation, gaming, photography, computer fonts etc. to make jaggies appear less evident.

  The sample 50 hz AC signal from cheap step down transformer

Ground reference signal

A very noisy house – 50 hz hum from house wiring  - open probe

Most of my work is digital but occasionally it crosses into the world of analog when wire length in signal cables begins to degrade the quality of the waveform which inevitably affects the ability of a digital interface to correctly determine logic signals properly at the receiving end.

Recently I was installing an environmental control system and found that the data train was being distorted by the effects of the long wiring – I was able to demonstrate the problem with an oscilloscope and take appropriate action with some signal conditioning using a couple of op amps as comparators. This problem needed to be fixed before the Pico arrived so I do not have sample screen captures but the effect was a rounding of the nice sharp corners of the square wave into something approaching triangular waves with rounded tops. Anyway, I don’t use CROs or DSOs much but they are useful and sorely missed when you need them.

From memory they looked something like:

The final signal was shaped into a nice square wave with no loss of data at all.  The knowledge of how a waveform appeared was invaluable in determining a solution.
What is the Pico 2205A DSO?

Most users of a cheap DSO will only take advantage of a small subset of the equipment’s abilities… as a matter of high probability this is likely for most test instruments of this complexity.

The Pico is a PC add-on that communicates with the PC via the USB port. All control is provided through an application called PicoScope (version 6 at the moment). Power is supplied entirely through a standard USB port (a USB 2.0 port in my case)

The Pico specs do not claim outlandish abilities for the price. This is a common feature of some advertised alternatives. This DSO is a capable oscilloscope and would suit anyone that falls into the occasional hobbyist mould. It would also suit a space poor work bench where a notebook computer already has a place and a small unobtrusive package (the Pico) would have little impact on the desk. At a few clicks, we can be testing a waveform without moving much more than a probe or two.

This is not a device targeted at the professional who needs a hundred megahertz or more of bandwidth. It is meant to be used by someone whose needs are a little less demanding in capability but not necessarily less in quality. Its rated bandwidth is only 25MHz but is suitable for most microcontroller based projects except when measuring clocks signals near that of the higher speeds available of recent MCUs or near that area. I assume that the bandwidth is as stated as I do not have the means to check this... it would not want to be much lower if the user is working with Arduinos, PICs and the like.

The Pico is enclosed in what looks to be a rugged ABS (a type of plastic that has a high impact resistance) case which looks as though it would handle a fair amount of physical abuse (not that I’d try it though). There are two standard BNC connectors for signal input and another for output from the function generator and a USB socket at the rear for a sturdy USB Type B plug – no mini or micro USB sockets here.

The PicoScope has two inputs and supplies two (x1/x10) probes of the same reasonable quality.  Most of the probes I have seen on later equipment have been very lightweight and feel a bit flimsy

No fiddly buttons or switches etc to contend with, so it is all software controlled (except for the x1 – x10 switch on the probes of course).

The Pico’s PC requirements are quite small by today’s standards, I think. A 300mHz Windows XP PC with 256mb RAM and 1gb free disk space and USB 1.1 – I doubt there would be too many notebooks with less specs on a bench top these days.

Measurement

The capabilities of this device are just within the average hobbyists needs, I think. Some hobbyists are quite advanced and may not be happy with a dso like this if money is not an issue.

I don’t have the means to produce calibrated signals these days as I no longer work in a lab but a simple multimeter can still provide some information about signals so that signal levels can be determined with some accuracy.

I performed some testing with PWM trains from an Arduino and after a quick calculation I set the Arduino to produce an output frequency of 976.5625Hz at pin 11 based on a base clock of 31250Hz and the divisor of 32. The Pico shows it as an average of 980.4Hz  I would expect the Arduino to be a bit more accurate than that as this shows an error of 0.4% Which is more correct? I will have to get hold of an accurate frequency meter or source a more accurate DSO at some stage.

Setting the duty cycle to 50% and reading off the voltage measurement on the display I got a reading of 2.856 volts. A 50% duty cycle square wave should average out on a voltmeter to pretty close to half the this measured value so multiplying this by 0.5 gives me 1.428 volts.  Measuring the voltage with my digital multimeter shows 1.429 volts. This looks pretty accurate to me! So I know that any low voltage logic value I read will be pretty close to the mark.

I was able to use the measurement tools with little difficulty and they seemed adequate for most basic functions.

You can also do some math with the waveforms ie adding, subtracting, inverting etc as well as perform the following types of measurements (below) simultaneously against any signal(s).

Above and beyond

But wait ! That’s not all ! The Pico is not just a DSO! It can also create waveforms!

The Function Generator/Arbitrary Waveform Generator can generate any of the waveforms below that are built into the PicoScope and also generate an arbitrary waveform derived from a template that is provided by the user.

Feeding the Waveform that the Pico generated back into itself allowed me to review the waveforms before injecting them into the target circuit.

Pros and Cons

Pros

Easy to set up wherever you are as long as you have your laptop or PC with you.

Great for a hobbyist and/or beginner.  CROs can teach you so much! And the price isn’t too bad. It is pretty much on par price and feature wise with some of the cheap DSOs eg RIGOL have one in this price range but it is a bit bigger but it doesn’t need a PC so this is both a pro and a con.

Versatile and has most of the basics.

The software is stable – I couldn’t crash it. It is also being kept up to date per the updates I have received already.

Seems to be accurate based on my measuring. Time will tell if I can get my hands on a Frequency Meter or a DSO with known accuracy.

Cons

No isolation of ground from USB but this is due to nature of the scope and its power source – The USB! Not having conventional grounding can lead to dangerous and even lethal situations of which a newer user may not be aware. Need to be careful using this with equipment connected to mains potentials even if you think you are measuring in low voltage areas. Also, floating grounds on battery laptops. Hmmm… I think this would not be good on anything but microcontroller voltages and non mains equipment.

Doesn’t FEEL like real CRO – no knobs, buttons and switches and the software doesn’t try to convey that look and feel either. Why does a computer program have to look like a program instead of a make believe CRO/DSO?  A person who has never used a bench CRO will probably take to it like a duck to water whilst a seasoned techie will find it awkward. Time and patience will probably eliminate the difference. I will say that after using a bench device with tactile knobs etc, you can learn to use it almost without looking and then quickly check your screen – not so with the PC based DSOs. You have to look at the screen and watch where you move the mouse and click. This is going to be hard to get used to… if one can!

Price could be a little cheaper I guess, but then, so could most things !

20V Peak to Peak is low. I had trouble finding a transformer in my junk box that wasn’t over that.

Conclusion

How far beyond reality do manufacturers claims go? I think I answered this earlier but the PicoScope 2205A does what the specs say it does or at least as much as I can determine. It is a great little versatile package

Is it worth the money? At AU$417 (about US$375), this does not seem to be a bad deal given the software which appears to be well supported. I have downloaded two updates already since originally installing the package.

I think I will still save up for a “real” DSO – only because of the range of equipment I work on – but it should be great for micros etc at a hackerspace or similar.