keychron_qmk_firmware/hhkb/doc/HHKB.txt

Alternative Controller for HHKB pro
===================================
I want to add vi cursor and mouse keys to HHKB. Original HHKB controller is not programmable and
firmware source code is not open. So, customizing HHKB needs to replace original controller with programmable one.
I used Teensy++ as alternative controller. Though a Teensy has enough ports to drive HHKB,
Teensy++ has clean pinout and it makes programing and wiring easier.

This is just a proof of concept for replacing controller of HHKB, not a complete firmware.

My prototype firmware source tree is here:
    github(http://github.com/tmk/tmk_keyboard)
This firmware is a port of my previous project:
    HHKB style Mod(http://geekhack.org/showwiki.php?title=Island:11930)
PJRC:
    Teensy++/Teensy(http://www.pjrc.com/teensy/)


Pros:
    * without pattern cutting, case mod  and soldering
    * can keep original controller intact
    * can change HHKB behaviour as you like(by C programming)

Cons:
    * void your warranty
    * unavailability of Teensy++/Teensy(because of PS3 cracking boom?)

Features:
    * customized keymap
    * more keymap layers
    * mouse keys for minimum mouse operation(never comfortable for normal use)
    * and more...(in the future)

Any suggestions or ideas are welcome.


NOTE:
    My HHKB is just "Professional". This means followings may not be applied to "Professional2".

DISCLAIMER:
    I'm not a professional for electronics and MCU programming. This may damage your HHKB.
    And my English writing is poor, I'm not sure I can convey my notions accurately.


Teensy++ installation
---------------------
Angled USB mini B adapter is used to install Teensy++ laterally.
(teensy_install.jpg)

Bread baord wires are used to connect Teensy++.
(teensy_wiring.jpg)
(connector_contact.jpg)


HHKB internal
-------------
HHKB pro has some chips on separate two PCBs.

Controller PCB:
    M38K07M4    Renesas MCU with USB function
                http://documentation.renesas.com/eng/products/mpumcu/rej03b0192_38k0ds.pdf

    (HHKB_controller.jpg)

Keyswitch PCB:
    HC4051      Analog Multiplexer: select a row line.
                http://www.alldatasheet.com/datasheet-pdf/pdf/203989/KODENSHI/KK74HC4051A.html
    LS145       BCD Decoder: select a column line.
                http://www.alldatasheet.com/datasheet-pdf/pdf/27373/TI/SN74LS145D.html
    BU9831      Non-volatile electronic potentiometer: for calibration?
                http://www.alldatasheet.com/datasheet-pdf/pdf/36387/ROHM/BU9831.html
    TP1684      Capacitive Sensing controller: no datasheet available.

    (HHKB_keyswitch.jpg)

    Topre original chip?
    (HHKB_TP1684.jpg)


Two PCBs are connected by 15 lines. Vcc and GND use 3 lines each, other 9 lines are for keyboard signaling.

    Keyswitch PCB connector                                 Teensy++ pins
    -------------------------------------------------------------------------------
     1  Vcc(5V)                                             5V
     2  Vcc(5V)
     3  Vcc(5V)
     4  TP1684    KEY: Low(0) when key pressed              PE6 input(with pullup)
     5  TP1684    KEY_PREV: assert previous key state???    PE7 output
     6  HC4051    A(bit0) select 8 rows(0 to 7)             PB0 output
     7  HC4051    B(bit1)                                   PB1 output
     8  HC4051    C(bit2)                                   PB2 output
     9  LS145     A(bit0) select 8 columns(0 to 7)          PB3 output
    10  LS145     B(bit1)                                   PB4 output
    11  LS145     C(bit2)                                   PB5 output
    12  LS145     D(enable) Low(0) enable selected column   PB6 output
    13  GND
    14  GND
    15  GND                                                 GND

    (HHKB_connector.jpg)


Keyswitch matrix
----------------
60 keyswitches in 8*8 matrix. It is ghost-free and bounce-free.

  COL 0     1       2       3       4       5       6       7
ROW ---------------------------------------------------------------
  0|  2     q       w       s       a       z       x       c
  1|  3     4       r       e       d       f       v       b
  2|  5     6       y       t       g       h       n       _NONE_
  3|  1     Esc     Tab     Control LShift  LAlt    LMeta   Space
  4|  7     8       u       i       k       j       m       _NONE_
  5|  \     `       Delete  Return  Fn      RShift  RAlt    RMeta
  6|  9     0       o       p       ;       l       ,       _NONE_
  7|  -     +       ]       [       '       /       .       _NONE_


Matrix diagram:
             +-------------------------+-+-+-+-+-+-+-+     Vcc
             |bias control?            - - - - - - - -     ---
             |                  3.9K*8 R R R R R R R R      |
    +--------^+      +--------+        - - - - - - - -      |  
    | TP 1684 |      | HC4051 <0-------|-|-|-|-|-|-|-|--|R|-+
    |         |capa. |        <1-------|-|-|-|-|-|-|-|--|R|-+
    |         |sense |        <2-------|-|-|-|-|-|-|-|--|R|-+
    |         <------|        <3-------|-|-|-|-|-|-|-|--|R|-+
    |         |      |        <4-------|-|-|-|-|-|-|-|--|R|-+
    |         |      |        <5-------|-|-|-|-|-|-|-|--|R|-+
    |         |calib.|        <6-------|-|-|-|-|-|-|-|--|R|-+
    |         <-+?   |        <7-------|-|-|-|-|-|-|-|--|R|-+
    +---V-----+ |    +-^-^-^--+        0 1 2 3 4 5 6 7  33K*8
       KEY ???  |      A B C         +-----------------+
        |   | +-^----+ | | |         |      LS145      |
    Vcc |   | |BU9831| | | |         +-^--^--^--^------+
    --- |   | +------+ | | |           A  B  C  D   +------+
     |  |   |          | | |           |  |  |  |   |      |
    1-3 4   5          6 7 8           9 10 11 12 13-15    |
    +--------------------------------------------------+   |
    |                connector                         |  ---
    +--------------------------------------------------+  GND
                    to controller
                                    

Signals charts:
    While pressing space bar, watched HHKB original controller signals by logic analyzer.
    Row and column is looping between 0-7 each for selecting a key.
    A key is scaned every about 15ms, so scan rate is 66Hz.

    (HHKB_chart1.jpg)

    Space bar locate at ROW:3 COL:7. A key is selected by HC4051(C,B,A) and LS145(C,B,A).
    Key state can be read on TP1684(4/KEY) while asserting low on LS145(D). 

    Usage of TP1684(5) is not clear. Controller seemed to output previous key state on this line.
    However key state can be read without using this signal.

    (HHKB_chart2.jpg)


Matrix scan pseudo code:
    for (row: 0-7) {
        SELECT_ROW(row);        // set HC4051(A,B,C)

        for (col: 0-7) {
            SELECT_COL(col);    // set LS145(A,B,C)

            _delay_us(40);

            if (prev_key_state(row, col)) {
                KEY_PREV_ON;
            }

            _delay_us(7);

            ENALBLE_COL();      // set LS145(D) to low

            _delay_us(10);

            if (KEY == 0) {     // read TP1684(KEY)
                // key pressed
            } else {
                // not pressed
            }

            KEY_PREV_OFF;
            UNALBLE_COL();      // set LS145(D) to high

            _delay_us(150);
        }
    }


Keymap layers
-------------
Followings are added layers with additional Fn keys.

see keymap.c

EOF