The audio network analyser is now here

Latest program ready for release isn’t a demo in the usual sense; it’s not designed to be used in lectures and talks, it’s designed for use in the lab.

Our students spend some of their first term here building an external audio interface based around the TI PCM2902 chip, and some of their second term taking a lot of readings of the frequency and phase responses of reactive networks. The former task is quite interesting and engaging, the latter task is somewhat tedious. So – why not use the external audio interface to build a network analyser capable of measuring the frequency and phase response of a passive network?

All you would need is a bit of software, and writing software is more fun than most of my other tasks, so that’s what I’ve spent some of the summer doing. It’s finally ready for release, and can be downloaded from here: Audio Network Analyser Program.

It was designed for use with the USB audio interfaces the students build here, which use default Windows drivers. Under Windows 7 these don’t always put the system into the right mode – hence the initial information screen that comes up at the start of the program. The software should work with other modems and operating systems, but the input levels might need adjusting, and I’ve not tested it.

Playing around should give you the idea of how it works: the only non-obvious points might be:

  • If you tick the “Accept Invalid” checkbox, the system will use values that might not be valid due to either saturation or very low input levels. Otherwise, these readings will be ignored.
  • If a reading comes in wrong (occasionally the phase is reported as being 90 degrees wrong, I’m still trying to track this one down), double-clicking on a reading will remove it. You can then replace it by moving the slider to the required frequency, and press “Single” to take a single reading at that frequency.
  • Click on the Bode plot to place a new pole. Double click on a pole to turn it into a zero (and vice versa). Drag it off the plot to remove it. Alternatively, poles and zeros can be entered using the windows that pop-up when pressing the “Poles” or “Zeros” buttons.

Next feature to add will be the additional of complex poles so we can use it with the resonant circuits the students come across later in their degree programmes.

If anyone wants to try it out, please let me know any successes/failures/comments.

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