PROTOCOL.md

Protocol for communicating to the Arduino over I2C

I2C all communication is initiated by i2c-master (RPI/Node) to the i2c-slave (Arduino).

This uses a two byte message:

cmd	option	value
4 bit	4 bit	8 bit

Cmd and option are 4 bit integers from 0-15. Value is a 8 bit integer from 0-255. Two bytes are always present (fixed length message), when value is not needed it is set to zero.

Commands

number	meaning
0-7	Set first-eigth strand color
8	Lighting effect
9	Set gear
10-15	future use

Options

Command

When cmd is 0-7 (set color), option controls which color is being set

number	meaning
0	red
1	green
2	blue

Lighting effect mode

When the cmd is 8, option controls what lighting effect mode should be used

number	meaning
0	Lighting effect off
1	Preset color
2	blink

Gear

When cmd is 9, option controls what to do with the gear

number	meaning
0	Off
1	On

Value

Value provides what value (from 0-255) to use and is dependant on the option selected.

Strand color

When cmd is 0-7 (set color), the value is the intensity of the color (0-255).

Special mode

When cmd is 8 (lighting effect mode) the value depends on the lighting effect used.

option	meaning	value
0	Lighting effects off	n/a (0)
1	Preset color	preset color (0-9)
2	blink	transition speed ms (0-255)

Set gear

Value is not used when cmd is 9, and should be set to 0

Examples

cmd	option	value	meaning
0	0	255	Set the first LED strand red to full intensity
3	2	128	Set the fourth LED strand blue to half intensity
8	0	0	All lighting effects off
8	1	2	LED color preset 2 (red)
8	2	100	Blink LED with 100ms transition
9	0	0	Turn off the gear
9	1	0	Turn on the gear