AVR spectrum analyzer

You can see the progress in the quarterfinal video:

Works:

• 1st button - backlight control
• 2nd button - 16 modes of spectrum and VU meter: https://cdn.hackaday.io/images/8052571408534158067.png
• 3rd button - 8 different symbols to draw spectrum bars
• 4th button - 3 different algorithms to draw spectrum: linear, linear with small values boosted, non-linear
• option jumper - vertical VU mode:
  

Missing:

• serial interface
• vertical VU not finished

A check-list of quarterfinal:

• The video (and a link to the video) no more than 2 minutes long on YouTube -
• 5 Project Logs
• The system design documents: schematic - https://github.com/CrazyChip/spectrum/blob/master/schematic/sa.pdf and the block diagram of the system - https://cdn.hackaday.io/images/3729271408312529258.png
• Licenses - everything under GPLv3

I soldered all the parts. The layout of the board is terrible but it works.

Some notes: 

• LCD connector is soldered upside down due one-sided PCB. The final version will be soldered on another side of the PCB.

• Trimmers are placed randomly. Not easy to find which does what. Too many trimmers and jumpers. I plan to simplify the input filters and reduce the number of these jump&trim.

• Optional (and different) connectors for audio input (e.g. 3.5mm socket) and power (e.g. small screw terminal block) would be convenient.

• Bad footprint of power connector.

• USB->serial chip on board (e.g. PL2303) would help with the external connection

So, looks like a list of several small improvements for the next version of the PCB :)

Block diagram added to show possible connections of the external devices

Kicad files committed to GitHub

https://github.com/CrazyChip/spectrum

Schematic in PDF also included:

https://github.com/CrazyChip/spectrum/blob/master/schematic/sa.pdf

 One-sided PCB is traced with Toporouter for prototype only.

A smaller two-sided PCB is planned after testing the prototype.

Youtube video shows a very early prototype implemented on Arduino using 20x4 character LCD.

Test signal is generated with Matlab (background music is not used as a signal).

Design stage: two low-pass filters - 1kHz and 16kHz - simulated on Multisim.