Picoscope 2208B MSO Review

There are few tools that are essential for an electronics hobbyist. When I started, I had a soldering iron, a multimeter and some components, and that was about it. That got me quite far because you can do simple debugging even with a multimeter, but once you start to do any communications, you will either work in the dark or get a signal analyzer, oscilloscope, or both. I reached that point about 9 months into my hobby, and eventually decided to get an entry-level PicoScope from Picotech. You can read the whole story from my PicoScope 2204 review from four years ago.

Long story short, I was extremely happy with my Picoscope, and I’ve been using Picotech’s products ever since in various projects. In the past years, I’ve also been collaborating with Picotech, so I’ve had the chance to use also their higher end models, including the frighteningly powerful 4-channel, 200 MHz, 16 bit PicoScope 5444B, which is really great but maybe even too hefty for my use. So when I was offered the chance to try out Picotech’s latest generation of their entry-level 2000 series published just a month ago, I was immediately in.

Without further ado, let’s get reviewing!

PicoScope 2000 series overview

The new PicoScope 2000 series is divided into roughly two groups of equipment: The entry models 2204 and 2205 range in price from 139€ for the 10 MHz 2-channel 2204A to 419€ 2205A and 2405A which are 25 MHz and have MSO (mixed-signal oscilloscope, i.e. it has 16 channel digital part as well) capability and 4-channels, respectively. Don’t let the low bandwith confuse you, even these models have sampling rates ranging from 100 MS/s to 500 MS/s, so you will get quite a lot of measuring power out of them.

Biggest limitation with 2204 and 2205 models is the buffer size, which ranges from 8 kS to 48 kS, so for longer captures than a few waveforms, only option is the continuous capture over USB which worked at a steady rate of 1 MS/s the last time I used it. So you can do unlimited capturing of signals around 100 kHz, but above that it’s the normal oscilloscope triggering business — that’s the way scopes have always worked from their beginnings, so it gets the job done as well.

  2204 2205 2206 2207 2208
Bandwith 10 MHz 20 MHz 50 MHz 70 MHz 100 MHz
Sample rate 100 MS/s 200 MS/s 500 MS/s 1000 MS/s 1000 MS/s
Resolution * 8 bit 8 bit 8 bit 8 bit 8 bit
Memory 8 kS 16 kS (48 kS w. MSO/4ch) 32 MS 64 MS 128 MS
Price (2015-22-05) 139 € 209 € 319 € 459 € 629 €
Options MSO or 4ch MSO or 4ch MSO or 4ch MSO or 4ch

*) Resolution for repeating signals can be increased to 12 bit with multiple samples
Continue reading Picoscope 2208B MSO Review

PicoScope 3206B Review

As I mentioned earlier, I got a PicoScope 3206B back in August. After a few months of use I have gathered enough experience with it to feel qualified to write a review on the device.

Those who haven’t yet done so, I suggest you to check out my earlier review of PicoScope 2204 – it covers a bit of my rationale for a USB scope, and the basic features of Picoscope software, which is the same for the whole PicoScope product line.

The 3206B is the top-of-the-line two-channel scope in the 3000 series. The prices have dropped a bit after the introduction of mixed signal version 3206B MSO, so for $1320, you’ll get this device with fairly impressive key feature set:

  • Two channels, and external trigger line
  • 200 MHz analog bandwith
  • 500 MS/s sampling rate
  • A huge 128 MS sample buffer
  • Arbitary waveform function generator (20 MS/s)
  • Two 250 MHz probes, storage bag and software CD

For full details, I suggest you to look up the 3200 series spec sheet from Picotech’s website. Let’s get started!

Unpacking the box

Picotech ships from UK and within EU, no additional taxes or import fees need to be paid. Both my deliveries from them have arrived promptly within two days, well packaged and in impeccable condition.

The scope comes in a cardboard box that also has space for the probes, a storage bag and software CD. Nothing too fancy, but works well for longer term storage, too.
Continue reading PicoScope 3206B Review

Color composite video decoding with Picoscope 3206B

I recently finished an improved version of the NTSC composite video decoder previously featured here at Code and Life. With the bigger buffer of Picoscope 3206B, I was able to capture enough samples per frame to add color. A Youtube demonstration video has just finished uploading and you can view it below.

I already talk a bit about the techniques used in the new version, as well as the new features. For the readers of this blog, I’m planning a more detailed technical explanation, which I’ll put up as soon as I get the infographics for that one done.

Enjoy the show! If you want to take a look at the sources (or better yet, have a 3000 series Picoscope at hand), you can grab the source package. My code is licensed under GPL, see README.txt inside the archive for details.

Update: Technical details now published! Implementation details to be added in another post a bit later.

Realtime Composite Video Decoding with PicoScope

After getting my Raspberry Pi and successfully trying out serial console and communication with Arduino, I wanted to see if I could use the Pi as a “display shield” for Arduino and other simpler microcontroller projects. However, this plan had a minor problem: My workstation’s monitor wouldn’t display the HDMI image from Pi, and neither had it had a composite input. Working with the Pi in my living room which has a projector with both HDMI and composite was an option, but spreading all my gear there didn’t seem like such a good plan. But then I got a crazy idea:

The Pi has a composite output, which seems like a standard RCA connector. Presumably it’s sending out a rather straightforward analog signal. Would it be possible to digitize this signal and emulate a composite video display on the PC?

The short answer is: Yes. The medium length answer is, that it either requires an expensive oscilloscope with very large capture buffer (millions of samples), or then something that can stream the data fast enough so there’s enough samples per scanline to go by. Turns out my Picoscope 2204 can do the latter just enough – it isn’t enough for color, but here’s what I was able to achieve (hint: you may want to set video quality to 480p):

What my program does is essentially capture a run of 500 000 samples at 150ns intervals, analyze the data stream to see whether we have a working frame (and because the signal is interlaced, whether we got odd or even pixels), plot it on screen and get a new set of data. It essentially creates a “virtual composite input” for the PC. There’s some jitter and horizontal resolution lost due to capture rate and decoding algorithm limitations, and the picture is monochrome, but if you consider that realtime serial decoding is considered a nice feature in oscilloscopes, this does take things to a whole another level.

Read on to learn how this is achieved, and you’ll learn a thing or two about video signals! I’ve also included full source code (consider it alpha grade) for any readers with similar equipment in their hands.

Continue reading Realtime Composite Video Decoding with PicoScope

Benchmarking Raspberry Pi GPIO Speed

UPDATE2: You may also want to check out my Raspberry 2 vs 1 GPIO benchmark!

UPDATED: 2015-02-15! This article has been very popular, so I’ve now updated all the benchmarks using the latest firmware and library versions. The scope has also been upgraded to a PicoScope 5444B with better resolution and bandwith than the earlier models. :)

main2015

Don’t try this at home! Shorting GND and VCC with a probe might fry your Pi and more!

Method and Summary of Results

The basic test setup was to toggle one of the GPIO pins between zero and one as fast as possible. GPIO 4 was selected due to easy access and no overlapping functionality. This is basically the “upper limit” for any signalling one can hope to achieve with the GPIO pins – real-life scenarios where processing needs to be done would need to aim for some fraction of these values. Here are the current results:

Language Library Tested / version Square wave
Shell /proc/mem access 2015-02-14 2.8 kHz
Shell / gpio utility WiringPi gpio utility 2015-02-15 / 2.25 40 Hz
Python RPi.GPIO 2015-02-15 / 0.5.10 70 kHz
Python wiringpi2 bindings 2015-02-15 / latest github 28 kHz
Ruby wiringpi bindings 2015-02-15 / latest gem (1.1.0) 21 kHz
C Native library 2015-02-15 / latest RaspPi wiki code 22 MHz
C BCM 2835 2015-02-15 / 1.38 5.4 MHz
C wiringPi 2015-02-15 / 2.25 4.1 – 4.6 MHz
Perl BCM 2835 2015-02-15 / 1.9 48 kHz

Shell script

The easiest way to manipulate the Pi GPIO pins is via console. Here’s a simple shell script to toggle the GPIO 4 as fast as possible (add sleep 1 after both to get a nice LED toggle test):

#!/bin/sh

echo "4" > /sys/class/gpio/export
echo "out" > /sys/class/gpio/gpio4/direction

while true
do
	echo 1 > /sys/class/gpio/gpio4/value
	echo 0 > /sys/class/gpio/gpio4/value
done

Continue reading Benchmarking Raspberry Pi GPIO Speed

Level Shifting 101

While writing my FAT+SD tutorial, I realized that my projects may soon contain both 3.3 V components like an SD card, and 5.0 V components like LCD displays or a MAX232 UART chip. Considering I only knew how to use resistors as voltage dividers, I decided to learn a bit more about voltage level shifting.

Having netted already two generous donations for this blog, I decided to spend the first one on $10 of components that could do the job, and employ my trusty, although not old, Picoscope 2205 to investage how they perform!

Simple low to high conversion: Flexible logic levels

When interfacing a 3.3V device with an AVR chip running at 5V, it is possible that no shifting is needed when communicating to the AVR chip. For example, the ATtiny13 datasheet specifies input low voltage as anything less than 0.3*VCC (1.5V when VCC=5V) and high as anything more than 0.7*VCC (3.5V when VCC=5V) – the 3.3V might be just enough to be reliably interpreted as “high” in your particular part combo. However, you might still want to consider the alternatives below, just to be sure.

Simple high to low conversion: Voltage dividers

The basic trick for lowering a voltage from, say 5V to 3.3V is to use two resistors in series, connected between the MCU pin and the ground. Because the voltage drop in each is proportional to the ohm value of each resistor, it’s easy to get any voltage between MCU VCC and ground from such a setup.

Basically, V0 = R1 / (R1+R2) * VCC. For example, if your MCU is providing 5V when an output pin is set high, you could have a 2k resistor (R2) and 3k resistor (R1) in series, resulting in 3V between the two resistors – that is because the 2k resistor “consumes” 2/5 of the overall voltage (5V->3V) and 3k resistor 3/5 of the voltage (3V->0V).

To see how it works in reality, I made a voltage divider from two 10k resistors, and measured both the voltage on MCU pin itself (the blue trace) and from between the two resistors (the red trace), when the MCU pin is set to alternate between low and high state 200 000 times a second (a 100 kHz square wave):


Continue reading Level Shifting 101

PicoScope 2204 USB Oscilloscope Review

PicoScope 2204 USB scope

One of the nicest things when starting a new hobby is that there’s just so many things you don’t yet have, and can thus look forward to researching and then maybe buying if the price is right. In electronics, you can pretty much get started with a $10 soldering iron, $25 multimeter, maybe a $30 programmer if you want to use microcontrollers, and then just buy cheap components to tinker with. But sooner or later, you start thinking about how nice it would be if you had an oscilloscope.

For me it took about nine months. I saw an article on using AVR as an RFID tag and noticed I could build a simple RFID reader with a few components. However, to really learn something, it would be nice to actually see the 125 kHz RFID carrier wave instead of fumbling blindly with the schematics. Additionally, I could use the scope to verify DIY D/A circuits, maybe debug serial protocols and much more. So I started researching.

Getting a used analog or digital scope from eBay was of course one option. However, old scopes are big, clunky and I don’t really have much table space. And if the scope fell out of use, it would be wasting space in a closet. New Chinese-made digital scopes from Owon and Rigol looked good and were relatively small and light. However, they had 640×480 or 800×600 displays and I had 2560×1600 30″ monitor sitting on my workspace, and being more of a software person, I eventually decided against them and chose to get a PC scope instead.

Options in USB scopes

Going through the options for digital scopes, there seemed to be a few price brackets:
Continue reading PicoScope 2204 USB Oscilloscope Review