It’s getting harder and harder to find spare time to work on projects. Firstly, the holidays at MIT are tiny compared to the holidays I get at Cambridge, and now that it’s finally Summer I am doing an internship which keeps me pretty busy 5 days a week, and I still want time to explore California and surrounding areas.

Anyway, I want to do a project that looks good and has some analogue electronics in it. I will build a system that listens to sound via a microphone, breaks the sound down into frequency bands and displays how loud each frequency band is using a strip of LEDs. It’s a similar idea to a Colour Organ but I want 7 frequency bands and 10 volume levels per frequency band (a total of 70 LEDs).

This is actually not that hard to do if you buy the right chips. An MSGEQ7 chip will take your audio signal and output 7 voltages representing the strength of each of your frequency bands. Then an LM3914 will take each voltage and light a subset of 10 LEDs to indicate the strength of that voltage.

Block diagram of the system

To make it a bit more interesting I want handle all of the frequency band detection with discrete components as opposed to using the MSGEQ7. I could do the same for the LM3914, however that would require using 10 comparators per channel giving a total of 70 comparators. This would be very repetitive, time consuming, space consuming and I wouldn’t learn much so I will keep the LM3914 in my design.

To replace the MSGEQ7 I will use one Multiple-Feedback Band Pass filter per channel, followed by a peak-detection circuit.