VU meter/ spectrum analyzer

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tiscando

Senior Member
Looks like this could be a complicated project, although you may be able to do this with an x1 or x2 chip to record analog levels, plus 7 or more audio filter circuits, or he may have done it just with bargraph ICs hooked to the filters.
 
R

Restus

New Member
SKL BOI said:
Hi

i want to make a vu meter or i think its called a spectrum analyzer for my computer to work exactly how this works:
http://www.youtube.com/watch?v=1pg9fMiVeW0

and i think that it would be best to use picaxe so could someone tell me how plz.

thanks

SKL BOI
Click to expand...
I would say that a spectrum analyzer is too much of a bold step for someone who asks how a specturm analyzer works but having said that, a UV meter is not a spectrum analyzer. Think of an oscilloscope only instead of displaying voltage vs. time you are showing frequency vs. Amplitiude. I have not watched the video but thought you might want to refine your question.
 
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Dippy

Moderator
Trying to do this (at the speed shown) with a PICAXE as a nitty-gritty audio processor and display driver is a no hoper I'm afraid.
I've done a similar thing for doppler display with a GLCD but had to use a dsPIC to get a good real-time display speed. I had about 40 bands in mine.
You may be able to do it if you can buy/find/make a secondary board which can do the processing.
For that you have 2 basic/easier options.
1. A board with numerous filters or an adjustable b/p filter to give you amplitude figures at certain Fbands.
2. A FFT processor
I used FFT for mine to allow lots of software adjustment.
I tried an experiment ages ago with an adjustable/programmable audio filter and got reasonable results but not as good as FFT. I can't remember the part number.
A multi-filter approach would probably allow a good display speed with a slower processor.

And you may also need some extra front-end electronics if it is intended to be a general purpose device - I don't know how "good" your electronics is.

Unless maybe there is a chip on the market that already does most of this for you? (I haven't looked - maybe something to search on would be graphic equalisers displays or something like that?)
 
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Andrew Cowan

Senior Member
The simplest way to make one of these would be to use filters and bargraph drivers (as tiscando says). That video is done with
This 16F877A Microchip PIC powered spectrum analyzer finally works in both dot and bar mode. Response time and accuracy has been optimized over the previous version. All 33 I/O lines of the 40 pin PIC are utilized, many with multi-mode. That is, any of the logic outputs are switched to logic inputs, tri-state and analog inputs on demand. So one I/O pin can become output, digital input and analog input. If software/hardware designed correctly, one logic I/O can be equivalent of 3 or even four I/O. No external switching logic required.
Click to expand...
Most bargraph display chips have a column/dot mode as seen in this video - until I read the above, I assumed that was how it was done. Get out your high pass/low pass filter calculations!

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hippy

hippy

Technical Support
Staff member
I agree with tiscando; a set of filters each with analogue bar graph LED drivers would be the easiest hardware solution and wouldn't need any processor. A fast processor could read the filter levels via ADC and then multiplex the LED's.

There are commercial products which have such equaliser displays and it could be that this example is simply someone who has ripped such a product apart, extended wires and bolted the display into their PC case. That's possibly the easiest route if you can find such a unit.

Another approach may be to run a PC software application which uses FFT or something to provide frequency band levels and then controls a PICAXE or other hardware via a serial or line printer port to set LED's. There are Active-X controls which can do that and can be dropped into user-written programs.
 
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