Using the Arduino CPU to demonstrate RE and CE

Kenneth Wyatt- July 30, 2012

Today's electronics hobbyists have turned from the use of discrete components to electronic "building blocks" based on open-sourced CPUs like the Raspberry Pi, Arduino, PIC/Basic Stamps and several others. I needed a low-cost test board I could use to demonstrate the issue of both radiated and conducted emissions and chose the Arduino Uno, as it's recently become very popular.

The Arduino is an open-sourced CPU with lots of built-in I/O - both analog and digital. It is also very easy to program using C# on PC, Linux or Mac platforms. The board includes a USB connector, which allows the user to upload new firmware very easily. There are also several books and programming references with sample code to assist the user in programming various features and functions. Even better, the boards are available for $20 to $30, depending on the source. I ordered mine from Amazon.

 
Because the board includes a USB and power connector, it's easy to measure the common-mode currents through cables plugged in. There is also a very strong 64 MHz harmonic (among others) from the 16 MHz crystal oscillator that was over the FCC Class B limit by 17 dB. Of course, this was measured using an unshielded board.
 

We also tested conducted emissions on the cheap 9V "wall-wart" switching power supply used to power the Arduino. Here's a shot with the cover removed. Note the lack of any line filtering!



The FCC Class B conducted emissions plot was not a pretty sight, being as much as 30 dB over the limt!



We added a couple "X" capacitors and a common-mode choke we happened to have kicking around. The series chokes were not found useful, so were removed.
 


And here's the resulting plot.



I guess the lesson here is, if you're going to use an OEM power supply, better ensure it has the proper regulatory labeling and then measure it to make sure!

In any case, I plan to use the Arduino board and power supply as test units for demonstrating the concept of both radiated and conducted emissions during my seminars. Best of all, the cost was very affordable. This could also be an easy way for you to demonstrate basic EMC concepts to your fellow employees and managers. Can you think of additional EMC-related experiments using the Arduino?

I'd like to thank Kevin and Vince of EMC Integrity in Longmont, Colorado (www.emcintegrity.com), for their assistance in making these measurements.