Teensy Thumb Keyboard

A few folks have asked for KiCad files for the i2c version. I was hoping to be able to make these at home and put them up on Tindie but I don't have the time at this point. 

You can find the files on my github page: https://github.com/AnthonyDiGirolamo/i2c-thumb-keyboard

Hopefully y'all will find this useful! If you make anything with it please let me know! I would love to see anything you come up with.

Connecting to the rpi and Hyperpixel4 screen works! I modified the hyperpixel4.dtsfile in the hyperpixel4 github repo. Thanks to the Malti project for the sample tca8418 dts file.

Here's the modified dts file. It requires the tca8418_keypad kernel module to be compiled and installed. I'll get instructions up for that eventually. Right now no interrupt pin is connected and the tca8418 interrupt is set to gpio 11 (the i2c clock line). I'd pick a different pin but there's no other ones available on the hyperpixel4 pinout. I'm also not using the touch version of the hyperpixel4 which also uses the same i2c bus. That may cause conflicts so I'll have to try that next.

Edit 2019-06-29: The keyboard and touch screen both seem to work, just not at the same time. Keys will not register if you are touching the screen / moving the cursor continuously. Likewise if you are pressing/holding keys down then touching the screen will not work. One at a time works just fine though!

/dts-v1/;
/plugin/;
/ {
  compatible = "brcm,bcm2708";
  fragment@0 {
    target = <0xdeadbeef>;
    __overlay__ {
      pinctrl-names = "default";
      pinctrl-0 = <0x1>;
    };
  };
  fragment@1 {
    target = <0xdeadbeef>;
    __overlay__ {
      dpi18_pins {
        brcm,pins = <0x0 0x1 0x2 0x3 0x4 0x5 0x6 0x7 0x8 0x9    0xc 0xd 0xe 0xf 0x10 0x11     0x14 0x15 0x16 0x17 0x18 0x19>;
        brcm,function = <0x6>;
        brcm,pull = <0x0>;
        phandle = <0x1>;
      };
    };
  };
  fragment@2 {
    target-path = "/";
    __overlay__ {
      i2c_gpio: i2c@0 {
        compatible = "i2c-gpio";
        gpios = <&gpio 10 0 /* sda */
        &gpio 11 0 /* scl */
        >;
        i2c-gpio,delay-us = <4>; /* ~100 kHz */
        #address-cells = <1>;
        #size-cells = <0>;
      };
    };
  };
  fragment@3 {
    target = <&i2c_gpio>;
    __overlay__ {
      /* needed to avoid dtc warning */
      #address-cells = <1>;
      #size-cells = <0>;

      ft6236: ft6236@5d {
        compatible = "goodix,gt911";
        reg = <0x5d>;
        interrupt-parent = <&gpio>;
        interrupts = <27 2>;
        touchscreen-size-x = <480>;
        touchscreen-size-y = <800>;
        touchscreen-x-mm = <85>;
        touchscreen-y-mm = <51>;
      };

      tca8418: tca8418@34 {
        compatible = "ti,tca8418";
        reg = <0x34>;
        irq-gpio = <&gpio 11 0x2>; // IRQF_TRIGGER_FALLING
        interrupts = <11 2>; // high-to-low edge triggered
        interrupt-parent = <&gpio>;
        interrupt-controller;
        keypad,num-rows = <6>;
        keypad,num-columns = <10>;
        // row | column | key-code  ex: 04,08,0010 q key
        linux,keymap = <
        0x00000069 // 01 0,0 left 105
        0x00010067 // 02 0,1 up 103
        0x0002006c // 03 0,2 down 108
        0x0003006a // 04 0,3 right 106
        0x00040005 // 05 0,4 4 5
        0x00050008 // 06 0,5 7 8
        0x00060009 // 07 0,6 8 9
        0x0007000a // 08 0,7 9 10
        0x0008000b // 09 0,8 0 11
        0x00090035 // 10 0,9 slash 53
        0x01000002 // 11 1,0 1 2
        0x01010006 // 12 1,1 5 6
        0x01020003 // 13 1,2 2 3
        0x01030007 // 14 1,3 6 7
        0x01040004 // 15 1,4 3 4
        0x0105000c // 16 1,5 minus 12
        0x01060027 // 17 1,6 semicolon 39
        0x0107000d // 18 1,7 equal 13
        0x01080028 // 19 1,8 apostrophe 40
        0x01090001 // 20 1,9 esc 1
        0x02000010 // 21 2,0 KEY_Q 16
        0x02010011 // 22 2,1 KEY_W 17
        0x02020012 // 23 2,2 KEY_E 18
        0x02030013 // 24 2,3 KEY_R 19
        0x02040014 // 25 2,4 KEY_T 20
        0x02050015 // 26 2,5 KEY_Y 21
        0x02060016 // 27 2,6 KEY_U 22
        0x02070017 // 28 2,7 KEY_I 23
        0x02080018 // 29 2,8 KEY_O 24
        0x02090019 // 30 2,9 KEY_P 25
        0x0300001e // 31 3,0 KEY_A 30
        0x0301001f // 32 3,1 KEY_S 31
        0x03020020 // 33 3,2 KEY_D 32
        0x03030021 // 34 3,3 KEY_F 33
        0x03040022 // 35 3,4 KEY_G 34
        0x03050023 // 36 3,5 KEY_H 35
        0x03060024 // 37 3,6 KEY_J 36
        0x03070025 // 38 3,7 KEY_K 37
        0x03080026 // 39 3,8 KEY_L 38
        0x03090029 // 40 3,9 grave 41
        0x0400002a // 41 4,0 leftshift 42
        0x0401002c // 42 4,1 KEY_Z 44
        0x0402002d // 43 4,2 KEY_X 45
        0x0403002e // 44 4,3 KEY_C 46
        0x0404002f // 45 4,4 KEY_V 47
        0x04050030 // 46 4,5 KEY_B 48
        0x04060031 // 47 4,6 KEY_N 49
        0x04070032 // 48 4,7 KEY_M 50
        0x04080036 // 49 4,8 rightshift 54
        0x0409000e // 50 4,9 backspace 14
        0x0500000f // 51 5,0 tab 15
        0x0501001d // 52 5,1 leftctrl 29
        0x05020038 // 53 5,2 leftmeta 125
        0x0503007d // 54 5,3 leftalt 56
        0x0504001a // 55 5,4 leftbrace 26
        0x05050039 // 56 5,5 space 57
        0x0506001b // 57 5,6 rightbrace 27
        0x05070033 // 58 5,7 comma 51
        0x05080034 // 59 5,8 dot 52
        0x0509001c // 60 5,9 enter 28
        >;
      };
    };
  };
  fragment@4 {
    target-path = "/";
    __overlay__ {
      rpi_backlight: rpi_backlight {
        compatible = "gpio-backlight";
        gpios = <&gpio 19 0>;
        default-on;
      };
    };
  };
  fragment@5 {
    target = <&ft6236>;
    __overlay__ {
      touchscreen-inverted-x = <1>;
      touchscreen-inverted-y = <1>;
    };
  };
  __symbols__ {
    dpi18_pins = "/fragment@1/__overlay__/dpi18_pins";
  };
  __local_fixups__ {
    fragment@0 {
      __overlay__ {
        pinctrl-0 = <0x0>;
      };
    };
  };
  __fixups__ {
    leds = "/fragment@0:target:0";
    gpio = "/fragment@1:target:0";
  };
  __overrides__ {
    rotate = <0>,"-5";
  };
};

Good news everyone! I'm working on a version 2.0 board that operates over i2c using the TCA8418. This will be my first project using SMD parts and so far so good.

For switches I picked the EVQ-Q2B03W. They are more pricey than your typical tactile switch but are worth the cost in my opinion. The datasheet says they require 0.5 N of force to press, are 3.1 mm tall and are rated at 2,000,000 presses. They are VERY light touch, it really doesn't require much more force than just typing on your phone screen.

It breaks out all the usual bits and includes a JST-PH connector for i2c that is compatible with Adafruit's PyBadge and PyGamer.

Next steps will be: 

• Seeing if this will work on raspberry pis without any other hardware. Note to self: checkout how the Malti project did this.
• Write an Arduino library (mostly done)
• Write a Micropython/Circuitpython library
• Look into getting them manufactured professionally. It took me about an hour to pick and place by hand and reflow.

Quick update: v1.1 is tested and works nicely! I'll update again if I can figure out how to get it on tindie.com.

I've gotten the code more or less in a shareable state. Still not perfect I'm sure, but good enough for now.

The layout for USB keyboarding is defined here:

https://github.com/AnthonyDiGirolamo/teensy-thumb-keyboard/blob/master/firmware/LayoutThumbKeyboard.h#L109

If you don't need a USB keyboard and are rolling your own hardware project then you can focus on this layout:

https://github.com/AnthonyDiGirolamo/teensy-thumb-keyboard/blob/master/firmware/LayoutThumbKeyboard.h#L74

There are three layers defined: base, shift, and Fn layers.

USB can be disabled by commenting out define USE_TEENSY_USB_KEYBOARD. 

All the keyboardy goodness is handled by the keyboard_update(); function called from inside the standard arduino loop().

If you don't need the keys to behave like a keyboard you can gut most of that example and just use key_matrix.update(); The KeyboardMatrix class handles reading the button states.

An alternative firmware option for a pure USB keyboard would be to run the excellent https://github.com/qmk/qmk_firmware.

Looks good so far. Some parts of the silkscreen didn't come out great. The lines between connected pads in the proto area are hard to make out. I'll have to update that in a later version. Electrically everything seems connected. I'll solder one up and test soon.

Turns out having an additional microcontroller in a raspberry pi project is pretty useful. I was able add backlight control and low battery monitoring to the keyboard with these connections. The Teensy is happy to output a PWM signal for backlight control. You can bind any key combination to change the PWM duty cycle and change the backlight brightness without any RPi intervention.

Low battery monitoring currently looks at the LBO pin that is pulled low if the battery dips below 3.2v. Alternative would be to have a voltage divider monitoring the BATT pin directly to get the full range of battery voltages similar to https://jeelabs.org/2013/05/16/measuring-the-battery-without-draining-it When the the LBO pin is low the Teensy can output serial message (over the default USB serial) that the RPi could monitor and then display a notification to the user.

Here are all the connections:

Rpi3B+   PowerBoost
PP2      5V
PP3      GND

Rpi3B+   Teensy 3.2/LC USB Surface Pads
PP48     GND
PP47     D+
PP46     D-
PP27     VBUS

Low battery monitoring:
Teensy D22 to Powerboost LBO

Backlight control:
Teensy D23 to BCM19 (GPIO pin 35 hyperpixel4 backlight control)

Rpi Power Test points from: https://www.raspberrypi.org/documentation/hardware/raspberrypi/schematics/README.md
Teensy 3.2/LC Pinout: https://www.pjrc.com/teensy/pinout.html
Hyperpixel4 Pinout: https://pinout.xyz/pinout/hyperpixel4
Powerboost 1000c Pinout: https://learn.adafruit.com/adafruit-powerboost-1000c-load-share-usb-charge-boost/pinouts

Everything looks good! All that's missing is a hole for the sliding power switch on the back cover. I wired the low bat pin on the Adafriut PowerBoost to the Teensy. When the battery is running low the teensy can send a message over the serial USB to the RPi3 and pop up a notification to the user. Software and code are pending and will be added to github soon. 

Keyboard behaves as a standard USB keyboard as expected using PJRC's excellent USB Keyboard and Mouse library: https://www.pjrc.com/teensy/td_keyboard.html There's some bonus functionality for using the D-pad to move the mouse cursor around. That turned out to be useful for the non-touch screen. By the way this really needs a touch screen, I've repeatedly tapped on the screen expecting something to happen despite knowing it doesn't work.

Time to get back to some pico-8, love2d and maybe tic-80 coding.

This was a challenging case to make. The hardest part was supporting the HyperPixel display and the RPi3 using only the mounting holes. I didn't want any pressure put onto the display to prevent cracks.

When I ordered the parts only the non-touch version of the HyperPixel was in stock so thats what I've modeled the case on. I've got a touch screen version on order and will make separate display bezels for each once that arrives.

Here's the front of the case with the modular keyboard and LCD mounted.

And the back side

This is where the RPi3 needs to be mounted:

That requires another layer. Here's the result. Temporary USB cable connecting to the Teensy:

The two halves of the case are mounted using self tapping plastic screws. Nicer M2.5 screws and hex nuts are used on the display and RPi3. The LCD bezel and case are held with screw free snap tabs.

Next up I added power and wired the Teensy directly to the USB solder pads.

This post is getting long so I'll add the final photos to Part 3

You might call this a PocketCHIP love letter.

Parts:

• Teensy Thumb Keyboard PCB
  https://hackaday.io/project/162281-teensy-thumb-keyboard
  https://github.com/AnthonyDiGirolamo/teensy-thumb-keyboard
• Teensy 3.2 - $19.80
  https://www.pjrc.com/store/teensy32.html
  https://www.adafruit.com/product/2756
• HyperPixel 4.0 - $49.95
  https://shop.pimoroni.com/products/hyperpixel-4?variant=12569485443155
  https://www.adafruit.com/product/3578
• PowerBoost 1000 Charger - Rechargeable 5V Lipo USB Boost @ 1A - 1000C - $19.95
  https://shop.pimoroni.com/products/powerboost-1000-charger-rechargeable-5v-lipo-usb-boost-1a-1000c
  https://www.adafruit.com/product/2465
• Lithium Ion Polymer Battery - 3.7v 2500mAh - $14.95
  https://www.adafruit.com/product/328
• Slide Switch - $0.95
  https://shop.pimoroni.com/products/spdt-mini-power-switch
  https://www.adafruit.com/product/805
• Raspberry Pi 3 - Model B+ - 1.4GHz Cortex-A53 with 1GB RAM -$35
  https://www.adafruit.com/product/3775
  https://shop.pimoroni.com/products/raspberry-pi-3-b-plus
• SD Card - $6.99
  https://www.amazon.com/Samsung-MicroSD-Adapter-MB-ME32GA-AM/dp/B06XWN9Q99
• Panasonic EVQ-PAC04M Tacticle Switche
  https://www.mouser.com/ProductDetail/667-EVQ-PAC04M
  https://www.digikey.com/products/en?keywords=EVQ-PAC04M
  60x $0.0177ea
• 1n4148 Zener Diodes 
  https://www.amazon.com/gp/product/B06XB1R2NK