September 1998, Issue 98

PIC'Spectrum
Audio Spectrum Analyzer

WRAP UP

I got the display looking quite good, with an interrupt routine taking ~50% of the available CPU time for video generation. The main program has time to do more than 10 FFT calculations per second, giving a true real-time display.

With my technique, the time spent in the video-generation code depends greatly on the image being displayed. If the screen is full of information, the time left for the main program is near zero. So, you can’t use this technique for all video-based projects.

To get satisfactory results with the video-display code, I sacrificed maintainability. Changes to the display may require tremendous efforts in keeping the real-time constraints unchanged. However, it works, and the basic principles may be used to get cheap video display devices like PIC’Spectrum.

For your next video-based project, try to do it with a software video only. If you have strict maintainability requirements, add a CRT controller chip or select a microcontroller with one built in. On the other hand, the FFT implementation is easily reused.

A final note: I’m sure this project wouldn’t be possible without a good simulator or an ICE. Thanks to Microchip for providing a good simulator for free on the Web!