Layout design for NPO capacitors


Some NPO (Non-POlarized) capacitors may have a stripe on their package. Since this can’t be a polarization indication, you might wonder what it means.

A capacitor is made of two conductive elements separated by a non conductive element. In cylindric capacitors (both radial and axial), there is a central core for one conductive element, and an outer shell that makes the second, with some non-conductive substrate in the middle.

The mark on an NPO point to the outer shell. This can be interesting if you need an end of your cap to be grounded. Grounding the outer shell provides isolation from EMI and prevents noise getting in the capacitor.

Check out the layout design tips and tricks that can take advantage of this.

Source: Hack a Day.


Audio Transformers article from Jensen

Here is an extract from the book Handbook for Sound Engineers about audio transformers, from Jensen engineer Bill Whitlock.

Audio Transformers chapter from Handbook for Sound Engineers.


Since the birth of audio electronics, the audio transformer has played an important role. When compared to modern miniaturized electronics, a transformer seems large, heavy, and expensive but it continues to be the most effective solution in many audio applications. The usefulness of a transformer lies in the fact that electrical energy can be transferred from one circuit to another without direct connection, and in the process the energy can be readily changed from one voltage level to another.

Ground design considerations on EDN

Here is a series of very interesting articles on how to handle grounding in a PCB design, to avoid hum and EMI, especially when working with both analog and digital (mixed signal) chips.

Other articles in the same topic:

If you’re into electronics and PCB design, check out where these articles come from, it’s a real gold mine of information and tips!

Active Pickguard project for Kinetis Challenge

Eli Hughes made this awesome PCB pickguard for his entry in the Freescale Kinetis Make It Challenge. It contains a Freescale Kinetis ARM Cortex M4 processor with DSP extensions to process the guitar signal, providing both an analog and digital audio output.

He also release a video with the details of all the maths and physics explained, as well as the hardware design.

Code and schematics are available here.