picadae/control

This folder contains the picadae control code.

The picadae control program consists of three parts:

• tiny : Keyboard solenoid driver
• ctrl : Keyboard central controller
• app : Monitor and command utility.

Architecture

The keyboard control hardware consists of 8 driver boards mounted above the solenoids on the keyboard assembly. Each driver board has 11 key driver circuits and can therefore control 11 piano keys. Each key driver circuit consists of an ATtiny85 microcontroller which controls a set of power transistors which in turn control the state of the solenoid. The solenoid can be in one of three states:

• off
• attack
• hold

The attack state is triggered by pulsing the the solenoid with a fast (250 microsecond to 30 millisecond) 36 volt pulse. The duration of the pulse determines the attack dynamic. The hold state then holds the key down during the sustain portion of the note.

All 88 ATtiny85 microncontrollers are attached to a single I2C bus which is shared with an Arduino Uno. The application computer communicate with the Uno via a serial connection. The Uno in turn translates messages between the ATtiny85 channel computers and the application computer.

Keyboard central controller : Arduino Uno Serial Interface

Read a register value of <count> bytes from channel <i2c-addr>

'r' <i2c-addr> <register> <count>

Write a register value of <count> bytes from channel <i2c-addr>

'w' <i2c-addr> <register> <count> <value-0> <value-1> ... <value-n>

Keyboard solenoid driver : ATtiny85 Firmware

PWM counter frequency and period. for each possible div setting with 16 Mhz system clock.

Value	Div	Frequency	Period
1	1	16 M	62.5 n
2	2	8 M	125 n
3	4	4 M	250 n
4	8	2 M	500 n
5	16	1 M	1 u
6	32	500 K	2 u
7	64	250 K	4 u
8	128	125 K	8 u
9	256	62500 Hz	16 u
10	512	31250 Hz	32 u
11	1024	15625 Hz	64 u
12	2048	7812.5 Hz	128 u
13	4096	3906.25 Hz	256 u
14	8192	1953.125 Hz	512 u
15	16384	976.6625 Hz	1024 u

Monitor and command utility : Python Utility