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+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
+
+
+
+
+
+