Some time ago I got some audio equipment in RACK housings. In one of them there was a 10-channel signal level indicator board and it asked to build a spectrum analyzer.
The board has ten AN6884 chips and 50 3mm red LEDs, but the module was adapted to indicate a voltage level of 100 V (it was radio equipment). The first thing I did was get rid of the voltage dividers, place the capacitors and replace the diodes with green and red 2x5 mm MILK.
It looks like this now.
The module started with the so-called "kick", now filters would come in handy.
The filters are two plates with 5 completely separate filters, connected by ground and signal. The power supply is 12 V, each filter has an artificial ground system and is powered from the main rail through a 1 k? resistor, thanks to which the system does not excite and the filters do not have any influence on each other (during tests with a common power supply and artificial ground, it happened often) .
Capacitors selected experimentally and like this: CH1 - 100nF, frequency - approx. 50Hz CH2 - 47nF, frequency - approx. 100Hz CH3 - 22nF, frequency - approx. 200Hz CH4 - 10nF, frequency - approx. 500Hz CH5 - 4.7nF, frequency - about 1kHz CH6 - 3.3nF, frequency - about 1.8kHz CH7 - 2.2nF, frequency - about 2.5kHz CH8 - 1nF, frequency - around 5kHz CH9 - 470pF, frequency - about 10kHz CH10 - 220pF, frequency - approx. 18Hz (too much here)
The sensitivity of each band is adjustable.
Tiles - thermo transfer. Figure in the attachment.
Everything is fine, but (as always, I have to ask) what is the threshold between individual LEDs? In addition, 5 LEDs per channel are still a little bit to talk about an analyzer - if it is about an "audio band blinker".
For a professional analyzer, there are not enough diodes, not enough bands and no specific division (thirds, octaves, or whatever), but I was supposed to call it Equalizer as some? Of course, this is a banded winkle (cool name) and is intended to please the eye.
Seriously, it's -10, -5, 0, +3, + 6dB (according to the note) AN6884, is a replacement for the KA2284, LB1403N chips.
5 LEDs per channel are not enough to talk about an analyzer
After several years of using it (10 points x 11 channels), it seems to me that a minimum of 20 points per channel and 10-16 channels would be optimal for home use. But who likes what. Justyna, as always, you do cool things from your recycled equipment
In my youth, I followed the line of least resistance and connected the Equalizer with 2x12 strands to the sliders with assembled sets of scales from Jablo. I made a separate box for the analyzer and glued the diodes to the quick. Most work soldering wires, but the effect was pretty cool.
I think a minimum of 20 points per channel and 10-16 channels would be optimal for home use.
For home, 10 points in 10 bands are enough. Ultimately, the smallest stage EQ has only 16 bands. As for the number of LEDs in the bollard - a lot depends on the thresholds of their arrangement. A good idea in the analyzer is the LM3915 (probably well-thought-out - eventually used for this purpose), where the thresholds for lighting the next LEDs are 3dB. (3916 is more suitable as a recording level indicator - therefore it has a "concentration" of thresholds around 0dB). Anyway, even some time ago there were designs of such analyzers, only that the outputs from the filters were "swept" and went to one LM3915, from which the outputs were only triggered by LEDs - also switched synchronously with the filters. Thanks to this, the current consumed by the spectrum analyzer has significantly decreased - assuming even 10 mA per LED for one LM it is only 100 mA but for 10 ... 1 A! Unfortunately, this economy made the system quite complicated and more difficult to start up. A similar design was even discussed on Elektroda: https://www.elektroda.pl/rtvforum/topic560625.html However, multiplexing has (apart from the undoubted advantage in terms of power consumption) and its drawbacks. However, in this particular case (topic), the project is actually interesting and effective. Certainly not as a spectrum analyzer (as I explained earlier), but as an eye-catching addition to the equipment - absolutely.
As always, I must praise you for using the elements and components that are left in the home, and for making everything from scratch. You made this analyzer nice and aesthetic, I mean tiles. The end result, i.e. the operation of the system, is also very nice.