Bendy SAO a Hackaday 2025 badge addon

This repo contain some notes and code how to get live a Bendy SAO badge addon. All work was done during the Hackaday 2025 conference in Berlin Please look at https://hackaday.io/project/198408-bendy-sao for more details.

If you want to use this addon with your Hackaday 2025 badge, please look for details in our another repo.

Caution

There is neccessary to keep pins GP1 and GP2 in log1 (higher than 0.7 × VDD => approx. more than 2.1 Volts). There is internal 20-50kOhm pull-up in addon chip, so if you connect just power, it will work well. But this also means, if you connect this addon to your Hackaton 2025 badge, then you need drive these pins in you badge to log1. In case when you drive these pins to low, addon will be held in reset mode.

Build

You can build it by (PlatformIO)[https://platformio.org] (run pio run in this directory).

Flash (write code into) ATtiny via UART converter

You can use Python MCU programmer with any USB to UART converter.

Wiring

UART to USB converter pin	Add-on pin
TX	GP2
RX	GP1

Fuses:

By default MCU uses 20MHz clock, for compatibility with Adafruit library needs to be switched to 16MHz. Be carefull, this can destroy your addon (if you do something wrong, you can lose access to programming interface). You can find details in Atmel's datasheet.

pymcuprog write -d attiny3224 -t uart -u /dev/usbdevice -m fuses -o 2 -l 0x7D

Image write to flash

pymcuprog write -d attiny3224 -t uart -u /dev/usbdevice -f ./.pio/build/attiny3224/firmware.hex --erase --verify

Interfacing with addon via I2C

I2C address is hardcoded to 0x2c

Memory (command) mapping

name	address
get status	0x00
get/set_mode	0x01
set led collor	0x02
chop reset	0x05

Error codes

name	code
ok	0x00
message to short	0xa0
message to long	0xa1
invalid data	0x10
unknown command	0xf0

Led animation modes

taken from BendySAO's repository

name	code
none	0
color wipe	1
theater chase	2
rainbow	3
rainbow cycle	4
theater chase rainbow	5

Message(s) structure

set/get mode message

 0                 
 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|     Mode ID   |
+-+-+-+-+-+-+-+-+

get status message

 0               1                  
 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7  
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vers. | Reser.|  Error Id     |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

set led color message

Led position id can be from 0 to 11

 0               1                  
 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  LED pos. id  |  Red          |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  Green        |  Blue         |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

microPython examples

... for those who rule over the serpent's language ...

microPython I2C lib. doc. here

Set animation mode

i2c1.writeto_mem(0x2c, 0x01, b'\x02')
. or .
i2c1.writeto_mem(0x2c, 0x01, b'\x04')

Set pixel color

This will disable animation

i2c1.writeto_mem(0x2c, 0x02, b'\x01\xf0\xf0\xf0')

Get animation mode

i2c1.readfrom_mem(0x2c, 0x01, 1)

Get device status

i2c1.readfrom_mem(0x2c, 0x00, 2)

Acknowledgements

https://hackaday.io/project/198408-bendy-sao

https://github.com/geekmomprojects/BendySAO/tree/main