Anubis guitar preamp

So, on electric guitars there are usually 2 or 3 pickups placed along the string.  You use switches to select which ones to use and the resulting sound depends on the pickup placement relative to the nodes and anti-nodes of the strings.

Some people get adventurous and drill holes in the guitars to add switches or knobs to allow for more control than the stock wiring affords.  I decided to make a preamp that would allow any combination and polarity of the pickups (even time-varying ones) without requiring modifications to the guitar's body or pick guard.

And so, the Anubis preamp for Fender/Squier Stratocasters was born!  There's a digital potentiometer and polarity switch for each of the three pickups.  They're all controlled by a microcontroller.  The control software can be edited and uploaded to the Anubis with an Arduino UNO board.

The volume and tone potentiometers have been replaced with a program selection encoder and two program value potentiometers.  Here's a shot of the boards.  The minimum order from the board house was 10 units, so I have some extras :)

And here's the board populated and installed on my Strat's pickguard.  There's a single IDC breakout cable that goes from a header on the board to the switching jack, the pickups, the battery, and the programming cable.

I've made a mostly dry recording of the guitar (direct injected, a little compression and reverb added) to demonstrate a few of the programs I've written for it so far.  In the order of recording they are:

1. Sample and hold: abruptly switching between randomly selected pickups.
2. Fast chorus: The pickups are amplitude modulated with low frequency sine waves that are 120 degrees out of phase with each other.  Sounds kind of like a three tap chorus.
3. Slow chorus: same as above, but with a slower modulation frequency.
4. Some of the 13 different pickup combination and polarity options. 


If I have time to do it over, I may try nice VCAs (like the  SSM2164) instead of digital potentiometers to avoid the annoying stepping/zipper noise. 

Here's a link to the GitHub repository for the microcontroller's software:
https://github.com/thecowgoesmoo/AnubisArray

As promised, here's the schematic:

And here's the bill of materials:

Description	mouser part number	unit price	quantity	line total	number on board
Switching jack	502-113X	3.15	1	3.15
IDC plug	617-09-18-520-7803	2.06	1	2.06
IDC header	571-7-146256-0	3.81	1	3.81
Amphenol flat cables	523-135-2801-020FT	1.75	1	1.75
Potentiometer	311-1901F-10K	2.87	2	5.74
Rotary encoder	652-PEC11L4125KN0020	1.43	1	1.43
7805 regulator	595-UA7805CKTTR	0.767	1	0.767	U8
regulator capacitors	77-VJ1206Y334KXJTBC	0.08	4	0.32	C13, C14, C15, C16
decoupling capacitors	77-VJ1206Y104KXJPBC	0.033	5	0.165	C7, C8, C12, C17, C11
output capacitor	77-VJ1206Y332KXJPBC	0.06	1	0.06	C1
crystal capacitors	77-VJ1206A220KXACBC	0.05	2	0.1	C9, C10
pull down resistors	652-CRT1206BY1002ELF	0.31	2	0.62	R8, R9
diodes	696-SML-LX1206YC-TR1	0.1	2	0.2	D3, D4
16 MHz crystal	774-ATS160SM-1	0.24	1	0.24	Y2
power supply resistors	71-CRCW1206J-100-E3	0.03	2	0.06	R10, R11
AD5222	584-AD5222BRZ1M	2.02	2	4.04	U2, U3
DG403	968-DG403DYZ	1.43	3	4.29	U4, U5, U6
9V battery holder	12BH610-GR	1.05	1	1.05
Atmega328	556-ATMEGA328-AU	2.58	1	2.58	U1