Table of contents

RoadTest: PICOSCOPE 2204A -  USB Oscilloscope

Author: baldengineer

Creation date: 31 Oct 2017

Evaluation Type: Test Equipment

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?: Other USB-based scopes.

What were the biggest problems encountered?: None. No issues from the moment I opened the box.

Detailed Review:

The PicoScope 2204A is a 2-channel USB-based scope with a built-in arbitrary waveform generator. Below I go into some of my thoughts and aspects I looked at during my RoadTest. The too-long-didn’t-read version is simple: buy one.

The Hardware

The PicoScope is an unassuming piece of hardware. It is much lighter than you might expect. That said, it has excellent build quality. While light, I never thought it was going to fall apart. The probes are excellent quality. I think the probes for a low-cost oscilloscope are the most critical part. After all, it is what you will be touching the most. I was surprised the 2204A is entirely USB powered. That means you can have a portable scope solution. Well, assuming you have a laptop to drive it.

Regarding specifications, you get two scope channels at 10 MHz with a max sample rate of 100 megasamples per second. The built-in memory is only 8 kilosamples. However, it does support a mode with streaming over USB to get longer acquisitions at slower time bases. For the price and bandwidth, I think the acquisition hardware is reasonable. I am not going to give any details on accuracy or precision. While I believe these to be accurate scopes, for around $100 you are not buying it for reference-level accuracy. That said, I have no complaints about its accuracy or precision regarding vertical (voltage) or horizontal (time).

The AWG

Personally, I do not use function generators or arbitrary waveform generators that often. That said, I do like having them available. In this case, I used the built-in AWG to test out some functions of the PicoScope. As an example, I thought to myself: could I find the driving frequency of the AWG?

I connected the AWG output directly to an input on the scope. Then I used an FFT view to look at the frequency content of the AWG. After changing the output frequency a few times, I noticed a bump around 1.5 MHz always appeared. Since that spike happens regardless of the output frequency, I believe this to be the driving frequency of the AWG. Is there anything unique or particular about that frequency? No. This measurement is an example of what you might make with this type of oscilloscope.

Side note, AWGs are a high-speed digital-to-analog converter (DAC). When you look at the waveform in the frequency domain, you can usually see the clock frequency that drives the DAC.  I do feel the need to point out that having this frequency show up on the output is NOT a bad thing. All DACs suffer from this “issue.” And on an AWG built-into a scope for about one-hundred bucks, I am still impressed with the performance.

The Software

Designing test and measurement software is tricky. The hardware almost always has technical details that the user may or may not want control over. So creating a user experience that is easy to use while giving control over everything can be difficult.

My one gripe, before I get into some good things, is the default colors. I am old fashioned. I think scope screens should be black, not white. Also, I found it strange the color bands on my probes were different from the default trace colors in the software. This issue was, of course, no big deal. The software offers many customizable options. Not only can you tune just about every color used, but you can also define hotkeys. (See, it did not take long to get back to a positive.)

In general, the PicoScope software over delivers. You might need to click around to find various scope functions. However, I think that is an issue with all oscilloscope software. The PicoScope software is consistent. For example, once you know how to set up a trigger, a serial decoder is set up in the same way.

Each time I’ve sat down to write about the PicoScope software, I find one more thing I didn’t expect. So here are some sections that caught my attention. This list is by no means complete or exhaustive. (In a way this is like playing a Zelda or Mario game. You get rewarded for continued exploration!)

Multiple Views

Being a PC application brings the benefit of multiple displays, or views. You are not limited to a single graticule trying to cram everything on to a tiny screen. The PicoScope application can display multiple viewports at the same time.

In this screenshot, I am demonstrating 3 time domain waveforms and 1 frequency domain (FFT) view. The 3 time domains show off the flexibility of how you can display channels. Here I am looking at both channels in one grid and then each channel in their own grid.

Serial Decoding

Another area that impressed me was serial decoding. If you are monitoring an I2C or CAN bus, analyzing the waveform edge by edge can take an enormous amount of time. Looking at the decoded data of the traffic is a huge time saver.

PicoScope is not the only oscilloscope with decode. So what is the big deal? A revenue-generating technique from the big scope companies is to charge for every individual feature they can. You will see this with features like “serial decode.” Some of the worst vendors change individually.

Pico Technology’s free to download software includes many built-in decoders. So whether you are looking at I2C, SPI, UART, or almost any serial bus that you can see with a 10MHz scope, you can get decode. No extra charge (after you acquire the waveform with one of their acquisition boxes.)

As someone who once decoded firmware byte-by-byte over an I2C EEPROM using an oscilloscope, I have a lot of respect for this "free" feature.

Math

Something I did not dive into but was thrilled to see: custom math channels. Most affordable class scopes today offer basic waveform math. Invert, add, subtract, maybe multiple two channels.

Again, the Picoscope software goes beyond affordable class. You can define your own equations. I doubt you will be able to think of a “measurement” this feature cannot support.

Custom Probes

Related to custom math functions are the custom probes. There are built-in presets for standard probes like x1 and x10 passives. There are also presets for current probes. The added bonus here is the custom probes.

You can create a “probe” that includes a lookup table or non-linear scaling. For example, what if you were measuring the output of a thermistor? You could use this custom probe capability to convert the signal into degrees Celsius (or Fahrenheit). On any class scope, this is a massively useful feature.

Measurements

The PicoScope software contains all the essential timing and voltage measurements you would expect to find. One aspect I like is the ability to “gate” measurements. Some scopes will just default to the first instance of a measurement on the screen. Sometimes it is the far left; sometimes it is the center. What’s great about a gating measurement is that you can define which part of the waveform to measure. So say you have an out-of-band signal to indicate the start of a transfer. You can “gate” the area of the waveform after that signal to measure the peak-to-peak voltage.

In this screenshot, I have placed rulers (the small squares on the bottom of the grid) around the trigger point. The measurement “Edge Count” is only counting how many edges it sees between the rulers.

When measurements are turned on, a table provides statistics on each of them. This detail is the kind of feature you typically only see in higher-performance, or higher cost, standalone scopes.

Support

I would like to thank Alan for answering all of my questions and offering some tips regarding the PicoScope. He gave me a good sense of the excellent support available from Pico Technology.

Tradeoffs

The 2204A’s bandwidth is limited. However, that may not be an issue. I keep coming back to the price point. This is an excellent entry-model scope. And I do not mean until you buy an oscilloscope from someone else, either. Pico Technology has a long line of impressive hardware. Once you learn how to use the low-end 10 MHz scope, you already have a good idea of how to use the higher bandwidth options. Some of them use the same software!

For low-speed hobby projects, like probing GPIO pins on an Arduino or even Raspberry Pi, 10 MHz is probably sufficient. If you are not sure that you need a scope yet, then for the price the 10 MHz PicoScope is an excellent option. If, on the other hand, you know that you need a scope but not sure how much bandwidth you need, look at your budget. Get the 10 MHz if you cannot afford the 25 MHz. Otherwise, get the bandwidth bump, you may need it in the future.

PicoScope vs. Standalone

A tougher decision is whether you should buy a PicoScope or a standalone scope. For another $100-150 you start to look at standalones that have much more bandwidth and sample rate. Honestly, before I got the PicoScope, I would usually push people towards the standalone. My attitude has now changed. Unless you need the compactness of a small bench scope, give the PicoScope a serious consideration. (Keeping in mind, if a laptop is sitting on your bench already, you now have a battery powered portable scope.)

(05-NOV-2017 Edit: This picture shows the BNC connectors as slightly yellow or even gold. They're not. They are all silver in color. I must have messed with the white-balance on this picture. -James)

The reason I now suggest considering the PicoScope is NOT just hardware “banner” specifications. The richness of the PicoScope software drives home the excellent value. You get features found in scopes that cost thousands of dollars in something that cost around one hundred dollars. Long story short, I am very impressed with the PicoScope 2204A. It will be showing up in some of the videos and tutorials I create, and I highly recommend purchasing one.