Picture of AVR acoustic spectrum analyzer
AVR acoustic spectrum analyzer, based on Atmega8 AVR microcontroller, operational amplifier, and few other components. Use any HD44780 compatible LCD or VFD, connect audio signal, and enjoy the effect :) You can build in this into your amplifier, pc, car-audio, or other device. On this moment device support following displays: 16*2, 20*2, 24*2, and 20*4. If you have one which this device not support, please contact me and i will try to adapt code for it. There are two pcb's which exactly fits behind the display, one for the 8*2 connector displays, and one for 16*1. You can attach a small keyboard to change display brightness (vfd also supported), change sensivity, choice the display effect. Settings are saved to the eeprom memory.

Project site:

And here is how it works on 20*2 VFD

"czulosc" and "janosc" are in polish, they means "sensivity" and "brightness" :) And they can be changed :)

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Step 1: Make board

Picture of Make board
Use the eagle project files or PDF's to make a PCB, choose 16*1 or 8*2 connector depending on your display. There is also top layer with components values. See schematic for part list. You can connect a small keyboard to 5pin connector, there is no pcb for keyboard, just use 5 buttons and connect all to the ground.

Step 2: Program the AVR

Picture of Program the AVR
First of all you need to program your AVR with code from the attachment, if you are using 16*2 display you need to flash the 16*2 version code, etc. Use any avr proggramer. You will need to setup fusebits as shown, for example on burn-o-mat, the avrdude GUI. You need to set the external crystal 16MHz, and activate the CKOPT fusebit. That's it.

39671 month ago

Hello, how is it possible to adapt this spectrum analyser to a another frequency range, for example 20 to 200 khz ?

TAGAPAW1 year ago

can i turn this project into like Samson D-1500 ? Sorry i'm new to Audio and electronic stuff, thank you very much

ultranewt2 years ago
what kind of input does this use? do you just plug your audio cable into it?
Bluesky02022 years ago
If I do it with arduino uno how can i change code for? And I don't understand audio ground be conected .
usbg3rd3 years ago
nice one buddy
there are 2 things i want to know
1- in which software u r simulating the avr chip
2- what is the general circutary for a reset switch that is active low
please reply indivusally and fast
just the thing i was looking for but i am pretty much a beginner in the world of electronics so first of all how do i turn the egal files into a pcb and second of all what screen and what size did you use? thanks
postlife3 years ago
What is the actual size of this unit in inches?
godofal4 years ago
awesome project!
i was thinking of something like this, remembered a similar project here (other one than this one) but this is exactly what i was hoping to make :D
gotta get the parts someday, this is really something i wanna have :P
are there plans for making a kit?
manekinen (author) 5 years ago
Attachment updated, program codes in previous one contained a little bug, so please download it again.
Mikkel3245 years ago

Excellent project, I have been looking for something like this for a while.

I will try putting it together later today, I have a lot of Noritake VFDs that I need to put to use.

There's just one thing I'm wondering about. I notice it uses the display in 4-bit mode. I have had some trouble with Noritake VFDs in 4 bit mode before, are there enough free IOs to make it use the display in 8 bit mode?

manekinen (author)  Mikkel3245 years ago
Hi! There is no even one free pin left. I have problems with this VFD too, but i don't think that is 4bit bus mode fault. My VFD has problem with changing the definiable chars while running, i can change them on start with no problems. When i try to change them while working, display just don't release busy flag and program hungs up, as seen on my movie, its reseted by watchdog - and it happens very often. I have tried a lot of tricks to avoid this but vfd keeps hunging up :(

And what are yours problems with VFD's? Can you test this analyzer on your VFD's and tell me if you have the same problems as me?

I have had many strange problems with using the Noritake VFDs in 4 bit mode, also that it won't go out of busy, leading programs waiting for the VFD to crash and other strange stuff. I have had this problem with both new and very old HD44780-compatible Noritake VFDs. The problems have always gone away when I have switched to 8 bit mode. This is very frustrating, but I don't know about any other solutions.

Are PB0-5 used for buttons? Maybe you could multiplex the buttons onto the VFD data bus.

Anders M.
manekinen (author)  Mikkel3245 years ago
You can throw away buttons and throw away two pins for selecting VFD and low prescaler - and you got 7 free pins. Maybe if i found some free time i will try to do this on 8bit mode and do more tests of these noritake vfd, which is, not 100% HD44780 compatible :( I don't know maybe there is some extra commands that pdf don't describes? I tried to switch off and on and do another init before sending definiable chars, i even edited compiler lcd library to make a little longer timings... same bug.
HuKePa5 years ago
Whats the name of 1st,2nd,3th song on the video?
 You use AVR Burn-o-Mat!
gism5 years ago
 Hi, witch character are you using to print the bars in the display? have you reprogrammed the display eeprom? I hope not.
I try to read the code but I'm a C18 kid and I don't get it...
manekinen (author)  gism5 years ago
Hi gism, you can define up to 8 your own chars in the HD44780 displays, you just send a proper command and display saves it into the ram memory. Look on the bottom of the program, there are these commands "deflcdchar" and data for it. The are saved in 0 - 7 cells. The code is in BASCOM AVR compiler.
gism manekinen5 years ago
thanks, I understand, I will have to read the datasheet to do this in C18.

guyfrom7up5 years ago
great job! have you thought about using nixie bargaphs, such as the in-13?
5 stars!
drbobbob5 years ago
I am just wondering but where did you get the VFD display?  I like how they look but I have not seen any cheap suppliers.
manekinen (author)  drbobbob5 years ago
I know, it's hard to get in decent price. Search on e-bay or similiar sites, i bought my for a 70PLN / 25$, and it's quite cheap.
manekinen (author) 5 years ago
I have just reuploaded rar archive and don't know why server is changing its extension and name to something random, it's not my fault. You can download this files from my site

Oh, and project is quite simple, it only looks complicated :) You do not have to do calibration if you don't want to, but it will be better if you do, you get better frequency response.
geeklord5 years ago
What do I use to open a .rar file?
amishx645 years ago
@ Everyone

If you guys are having trouble getting the right project file downloaded 
all you guys need to do is change the file extension on file you downloaded from .tmp to .rar

so instead of FP3YICPG3KY0NSJ.tmp
it should say FP3YICPG3KY0NSJ.rar

If you can’t see the file extension, go to ‘Tools’ –> ‘Folder options’ –> UNcheck “hide file extensions for known file types”

Hope this helps.


The rar file doesn't seem to work for me?