Probe a Circuit with the Power Off (EE Tip #14)

Imagine something is not working on your surface-mounted board, so you decide use your new oscilloscope. You take the probe scope in your right hand and put it on the microcontroller’s pin 23. Then, as you look at the scope’s screen, you inadvertently move your hand by 1 mm. Bingo!ComponentsDesk-iStock_000036102494Large

The scope probe is now right between pin 23 and pin 24, and you short-circuit two outputs. As a result, the microcontroller is dead and, because you’re unlucky, a couple of other chips are dead too. You just successfully learned Error 22.

Some years ago a potential customer brought me an expensive professional light control system he wanted to use. After 10 minutes of talking, I opened the equipment to see how it was built. My customer warned me to take care because he needed to use it for a show the next day. Of course, I said that he shouldn’t worry because I’m an engineer. I took my oscilloscope probe and did exactly what I said you shouldn’t do. Within 5 s, I short-circuited a 48-V line with a 3V3 regulated wire. Smoke and fire! I transformed each of the beautiful system’s 40 or so integrated circuits into dead silicon. Need I say my relationship with that customer was rather cold for a few weeks?

In a nutshell, don’t ever try to connect a probe on a fine-pitch component when the power is on. Switch everything off, solder a test wire where you need it to be, grab your probe on the wire end, ensure there isn’t a short circuit and then switch on the power. Alternatively, you can buy a couple of fine-pitch grabbers, expensive but useful, or a stand-off to maintain the probe in a precise position. But still don’t try to connect them to a powered board.—Robert Lacoste, CC25, 2013

High-Bandwidth Oscilloscope Probe

Keysight Technologies recently announced a new high-bandwidth, low-noise oscilloscope probe, the N7020A, for making power integrity measurements to characterize DC power rails. The probe’s specs include:

  • low noise
  • large ± 24-V offset range
  • 50 kΩ DC input impedance
  • 2-GHz bandwidth for analyzing fast transients on their DC power-rails KeysightN7020A

According to Keysight’s product release, “The single-ended N7020A power-rail probe has a 1:1 attenuation ratio to maximize the signal-to-noise ratio of the power rail being observed by the oscilloscope. Comparable oscilloscope power integrity measurement solutions have up to 16× more noise than the Keysight solution. With its lower noise, the Keysight N7020A power-rail probe provides a more accurate view of the actual ripple and noise riding on DC power rails.”


The new N7020A power-rail probe starts at $2,650.

Source: Keysight Technologies 

WaveSurfer 3000 Oscilloscopes with MAUI

Teledyne LeCroy recently introduced the WaveSurfer 3000 series of oscilloscopes. The series features the MAUI advanced user interface, which “integrates a deep measurement toolset and multi-instrument capabilities into a cutting edge user experience centered on a large 10.1” touch screen,” the company stated in a release.

Source: Teledyne LeCroy

Source: Teledyne LeCroy

Essential characteristics, specs, and features include:

  • Bandwidths from 200 MHz to 500 MHz, with 10 Mpts/ch memory and up to 4 GS/s sample rate.
  • Multi-instrument capabilities such as waveform generation, protocol analysis, and logic analysis
  • 130,000 waveforms/second with waveform update, as well as waveform playback and WaveScan search/find
  • An advanced active probe
  • A comprehensive toolset featuring powerful math and measurement capabilities, sequence mode segmented memory, and LabNotebook

The WaveSurfer 3000 is available in four different models (200 MHz, two-channel to 500 MHz, four-channel) with prices ranging from $3,200 to $6,950.

Source: Teledyne LeCroy

One Professor and Two Orderly Labs

Professor Wolfgang Matthes has taught microcontroller design, computer architecture, and electronics (both digital and analog) at the University of Applied Sciences in Dortmund, Germany, since 1992. He has developed peripheral subsystems for mainframe computers and conducted research related to special-purpose and universal computer architectures for the past 25 years.

When asked to share a description and images of his workspace with Circuit Cellar, he stressed that there are two labs to consider: the one at the University of Applied Sciences and Arts and the other in his home basement.

Here is what he had to say about the two labs and their equipment:

In both labs, rather conventional equipment is used. My regular duties are essentially concerned  with basic student education and hands-on training. Obviously, one does not need top-notch equipment for such comparatively humble purposes.

Student workplaces in the Dortmund lab are equipped for basic training in analog electronics.

Student workplaces in the Dortmund lab are equipped for basic training in analog electronics.

In adjacent rooms at the Dortmund lab, students pursue their own projects, working with soldering irons, screwdrivers, drills,  and other tools. Hence, these rooms are  occasionally called the blacksmith’s shop. Here two such workplaces are shown.

In adjacent rooms at the Dortmund lab, students pursue their own projects, working with soldering irons, screwdrivers, drills, and other tools. Hence, these rooms are occasionally called “the blacksmith’s shop.” Two such workstations are shown.

Oscilloscopes, function generators, multimeters, and power supplies are of an intermediate price range. I am fond of analog scopes, because they don’t lie. I wonder why neither well-established suppliers nor entrepreneurs see a business opportunity in offering quality analog scopes, something that could be likened to Rolex watches or Leica analog cameras.

The orderly lab at home is shown here.

The orderly lab in Matthes’s home is shown here.

Matthes prefers to build his  projects so that they are mechanically sturdy. So his lab is equipped appropriately.

Matthes prefers to build mechanically sturdy projects. So his lab is appropriately equipped.

Matthes, whose research interests include advanced computer architecture and embedded systems design, pursues a variety of projects in his workspace. He describes some of what goes on in his lab:

The projects comprise microcontroller hardware and software, analog and digital circuitry, and personal computers.

Personal computer projects are concerned with embedded systems, hardware add-ons, interfaces, and equipment for troubleshooting. For writing software, I prefer PowerBASIC. Those compilers generate executables, which run efficiently and show a small footprint. Besides, they allow for directly accessing the Windows API and switching to Assembler coding, if necessary.

Microcontroller software is done in Assembler and, if required, in C or BASIC (BASCOM). As the programming language of the toughest of the tough, Assembler comes second after wire [i.e., the soldering iron].

My research interests are directed at computer architecture, instruction sets, hardware, and interfaces between hardware and software. To pursue appropriate projects, programming at the machine level is mandatory. In student education, introductory courses begin with the basics of computer architecture and machine-level programming. However, Assembler programming is only taught at a level that is deemed necessary to understand the inner workings of the machine and to write small time-critical routines. The more sophisticated application programming is usually done in C.

Real work is shown here at the digital analog computer—bring-up and debugging of the master controller board. Each of the six microcontrollers is connected to a general-purpose human-interface module.

A digital analog computer in Matthes’s home lab works on master controller board bring-up and debugging. Each of the six microcontrollers is connected to a general-purpose human-interface module.

Additional photos of Matthes’s workspace and his embedded electronics and micrcontroller projects are available at his new website.




User-Extensible FDA for Real-Time Oscilloscopes

Keysight Technologies recently announced the availability of a frequency domain analysis (FDA) option, a user-extensible spectrum frequency domain analysis application solution for real-time oscilloscopes.

Source: Keysight Technologies

Source: Keysight Technologies

The FDA option extends the capabilities of Keysight Infiniium and InfiniiVision Series oscilloscopes by enabling you to acquire live signals from the oscilloscope and visualize them in the frequency domain, as well as make key frequency domain measurements.

Option N8832A-001 includes the application, the application source code for user extensibility, and MATLAB software. These tools enable you to extend an application’s capabilities to meet their current and future testing needs.

With the FDA application, you can address a variety of FDA challenges such as:

  • Power spectral density (PSD) and spectrogram visualization
  • Frequency domain measurements in an application including relevant peaks in the PSD and measurements such as occupied bandwidth, SNR, total harmonic distortion (THD ), spurious free dynamic range (SFDR), and frequency error
  • Oscilloscope configuration through the application to allow for repeatable instrument configuration and measurements; optionally includes additional SCPI commands for more advanced instrument setup
  • Insertion of additional custom signal processing commands prior to frequency domain visualization, as needed, for more advanced analysis insight
  • Live or post-acquisition analysis of time-domain data in MATLAB software

Source: Keysight Technologies