Designing a Spectrum Analiser Graphic Equilizer

Thread Starter

Maglatron

Joined Nov 3, 2023
154
I need to make a spectrum analiser from the bar-graph LED's I've included the datasheet, I'm alright at using arduino, I want the left side to be low frequency 32hz and the to the right 16000hz. I need the decibels to contol the hight that the LED bar thats lit I am aware that there is a pdf from june 1978 that explains how to make one but its 10 x 10 and I want to have a considerable amount more pdf included and it starts on page 27. https://worldradiohistory.com/UK/Electronics-Today-UK/70s/ETI-1978-06-78.pdf
I am perhaps looking for another approach! thanks for having a look!
 

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Thread Starter

Maglatron

Joined Nov 3, 2023
154
About the dual thread I don't know how to delete one! accident!


Mod: Deleted OK. :)
 
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Thread Starter

Maglatron

Joined Nov 3, 2023
154
I know this is a big ask but can hou do a mock-up in ltspice for the 20 column 30 row and show me how this would be setup, so I can get a visual and some insight into how the the LM3914 work in unison. I'm struggling to know where the analog signals input into the circuit! if or when you have the time? thank you!
 

Thread Starter

Maglatron

Joined Nov 3, 2023
154
Ok so I have worked out how to use an LM3914 to go up to 10 LED's with a varying signal from 0-5volts
Next I learned how to cascade the LM3914 to light 30 LED's with a varying signal from 0-12volts
Thats sorts out 1 column. So I guess I have to do that 20 times for all the columns.
Now how do I make musical signal into signals of up to 12volts and differentiate the signal to light each column with the correct frequency band? from 32hz to 16khz
 
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BobTPH

Joined Jun 5, 2013
8,664
20 bandpass filters, 20 amps, and 20 peak detectors.

Look up Salken-Keyes bandpass filter. You will need precision resistors and capacitors throughout.
 

Thread Starter

Maglatron

Joined Nov 3, 2023
154
ok I've followed a video and I get to this point I don't understand what the graph shows, what dB is or why at 20kHz it's equal to 1dB from 4dB I need a bit of a nudge and a clear explaination of whats going on here I understand that this is a low pass filter
 

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LesJones

Joined Jan 8, 2017
4,172
dB is the 10 times the log (base 10) of the ratio of the power levels at two points in a circuit. For example the input and output of an amplifier or filter. Google decibel definition.

Les
 

Thread Starter

Maglatron

Joined Nov 3, 2023
154
thanks I'm uploading what I have done yesterday, the low pass filter - when it reaches 20kHz the decibels go to 1 dB, and the high pass filter - when it reaches 20Hz it goes to 1 dB again, I think this number 1 dB is significant why do we try to aim for 1 dB
 

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LesJones

Joined Jan 8, 2017
4,172
I see no reason in particular to aim for 1 dB attenuation. It is your choice. I think it is more normal to quote the cutoff frequency of a filter as the frequency at which the attenuation is 3 dB more than in the passband of the filter.

Les.
 

Thread Starter

Maglatron

Joined Nov 3, 2023
154
I don't understand what attenuation means, google says the reduction of force, effect or value of something can you explain please?
 

BobTPH

Joined Jun 5, 2013
8,664
Reduction in loudness when talking about audio.

1 db is a barely perceivable reduction.

3db is about where you would notice the reduction.

6db is reduced to half.
 

BobTPH

Joined Jun 5, 2013
8,664
You would have to know where you started. db is a relative measure, it is the ratio of two levels.

No matter where you started -6db means 1/2. But be careful, that can mean either voltage or power. 1/2 power is voltage divided by sqrt(2).

Just to confuse things more, there is dbV which is relative to 1V and dbm, which is relative to 1 mW.

So 6 dbV would mean 2V. -6dbV would be 0.5V.

You would benefit greatly by taking an introductory course in electronics, do an online set of tutorials if you cannot access a real college course. This site has a pretty good set of tutorials.
 
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