LED Audio Spectrum Display


An LED bar graph fabricated on a perf board. Some of the columns are lit up.This project came about, as usual, by accident. I was rooting through my box of IC’s for another project and came across a chip that I must have ordered sometime in the past and forgot about: the MSGEQ7, a “Seven Band Graphic Equalizer” chip. Not the best name — the chip doesn’t do any sort of equalization; it just analyzes an audio signal to generate information that can drive a display.

When I looked up the datasheet, it dawned on me that I had ordered the chip at one point with the intent of making something along the lines of a sound organ. Now that I had looked it up, though, I thought it would be more interesting to make bar-graph display that I could integrate into some future project.

This is a typical application for this chip and some quick web surfing turned up a few descriptions of arduino-based projects that put the chip to just such a use [1,2,3,4]. Between their descriptions and plenty of sample code, it didn’t seem like that big a task to roll my own.

So, let me describe what I did. The overall goal was to take an audio signal, feed it to the MSGEQ7 chip, and have it essentially break the signal into seven frequency bands, i.e., take the signal and display it very coarsely in frequency domain — sort of a poor man’s FFT.

Details are below, or skip right the demo video to see a working version of the display.

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SOTA: Hermannskogel (OE/WI-001)

I think it is due to a reshuffle of Austrian SOTA summits, but according to the current database, there is only one summit in the Vienna (Wien) region, WI-001, Hermannskogel. I guess that made the choice of which peak to activate easy.

The Hermannskogel is the highest point near Vienna, and up to World War I, served as the cartographic zero point for Austria-Hungary. The Habsburgwarte, pictured here, is a rebuilt stone tower that sits on top of the hill and sports a variety of antennas and radomes.

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SOTA: Cabeza Arcon (EA4/MD-053)

A view from the peak featuring my unusual choice of footwear for a mountain hike.

For my last summit activation in Spain on this trip, I had two enticing options: first, I could aim for some of the ten-point peaks that lie along ridges or I could activate a peak for the first time. There are two good prospects in the first category: the peaks of Valdemartin (EA4/MD-004), Cabezas de Hierro (EA4/MD-002), and the Asómate de Hoyos (EA4/MD-006) all along one trai, and it looks like that trailhead could be reached by taking the ski lift up from the Estacion de Esqui de Valdesqui (presuming it runs in the summer). Similarly, Najarra (EA4/MD-013) and Bailanderos (EA4/MD-011) lie along a trail, which could probably be accessed by parking at 40.82797N x 3.83015W.  In fact, it might be easier to reach Asómate de Hoyos by continuing west from Bailandreos rather than east from Cabezas de Hierro.

Predictably, I went for the first-time activation of EA4/MD-053, Cabeza Arcon. This is in no way a technically difficult peak, so I assume that it was recently added to the list of summits.

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SOTA: Nevero (EA1/SG-003)

Looking at SOTAmaps, several associations overlap to the north of Madrid. I realized that without really going too far out of my way, I could visit a ten point peak in the EA1/SG association, which would put me over the top for gold level on the SOTA mountain explorer award. I’m not that much into awards, but why not? Having flown 8000 km to get here, another 20 km on the road is a drop in the bucket.

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SOTA: Cerro del Castillo (EA4/MD-052)

Recently, I attended a conference in Madrid and had another one scheduled a week later in Vienna. Instead of flying back to Madagascar between them (insane), I decided to take a few days leave in Spain (sane and fun).

There are plenty of mountains within an hour’s drive of Madrid, and many of these peaks are found in national parks. Just to the other side of that central range is the historic city of Segovia, so I booked a hotel a few kilometers outside Segovia.

Between Madrid and the hotel, I identified Cerro del Castillo (EA4/MD-052) as a target of convenience. It is a four-point summit in a region full of ten point summits, but I thought that I could do it in what remained of the afternoon after checking out of the hotel in Madrid and picking up a rental car at the airport.

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