The Elf Membership Card has 8 data switches, 3 mode switches, and a IN push button on its front panel. The data is displayed on 8 LEDs (binary). It is a error prone but educational task to "switch in" in (load) the program.

I have an old external keypad because my old notebook did not have a numeric keypad. The keys looks similar to those old Elf hex keypads, why not use this spare keypad for the Elf Membership Card? It is a Cherry keyboard and I have other Cherry keyboard with the same key caps.

Hardware

Cherry Keypad G84-4700, original key caps

LTP-305 Dot Matrix Display

Microdot_pHAT on Raspberry Pi Zero

Software for the Raspberry Pi

No special software needed. Keyboard drivers are already built in.

• Linux Keycode Table http://www.comptechdoc.org/os/linux/howlinuxworks/linux_hlkeycodes.html
• http://xahlee.info/linux/linux_keyboard_tools.html
• https://wiki.archlinux.org/index.php/Map_scancodes_to_keycodes

Mapping scancodes to keycodes is universal and not specific to Linux console or Xorg, which means that changes to this mapping will be effective in both.

pi@cosmac:~/elf/RaspiElf/tools $ udevadm info /dev/input/by-path/*-usb-*-kbd
P: /devices/platform/soc/3f980000.usb/usb1/1-1/1-1.2/1-1.2:1.0/0003:046A:0014.0002/input/input1/event0
N: input/event0
S: input/by-id/usb-046a_0014-event-kbd
S: input/by-path/platform-3f980000.usb-usb-0:1.2:1.0-event-kbd
E: BACKSPACE=guess
E: DEVLINKS=/dev/input/by-id/usb-046a_0014-event-kbd /dev/input/by-path/platform-3f980000.usb-usb-0:1.2:1.0-event-kbd
E: DEVNAME=/dev/input/event0
E: DEVPATH=/devices/platform/soc/3f980000.usb/usb1/1-1/1-1.2/1-1.2:1.0/0003:046A:0014.0002/input/input1/event0
E: ID_BUS=usb
E: ID_INPUT=1
E: ID_INPUT_KEY=1
E: ID_INPUT_KEYBOARD=1
E: ID_MODEL=0014
E: ID_MODEL_ENC=0014
E: ID_MODEL_ID=0014
E: ID_PATH=platform-3f980000.usb-usb-0:1.2:1.0
E: ID_PATH_TAG=platform-3f980000_usb-usb-0_1_2_1_0
E: ID_REVISION=0100
E: ID_SERIAL=046a_0014
E: ID_TYPE=hid
E: ID_USB_DRIVER=usbhid
E: ID_USB_INTERFACES=:030101:
E: ID_USB_INTERFACE_NUM=00
E: ID_VENDOR=046a
E: ID_VENDOR_ENC=046a
E: ID_VENDOR_ID=046a
E: MAJOR=13
E: MINOR=64
E: SUBSYSTEM=input
E: USEC_INITIALIZED=69042133468
E: XKBLAYOUT=gb
E: XKBMODEL=pc105

showkey --scancodes

evdev:input:bvpe-

File /etc/udev/hwdb.d/10-hexkeypad.hwdb

evdev:input:b*v046ap0014* # ML4700
 KEYBOARD_KEY_45=a  # bind numlock to A
 KEYBOARD_KEY_62=b  # bind /       to B
 KEYBOARD_KEY_37=c  # bind *       to C
 KEYBOARD_KEY_01=d  # bind ESC     to D
 KEYBOARD_KEY_1d=e  # bind Ctrl    to E
 KEYBOARD_KEY_38=f  # bind Alt     to F

pi@cosmac:~ $ ls -l /dev/input/by-id/
total 0
lrwxrwxrwx 1 root root 9 May 14 20:23 usb-046a_0014-event-kbd -> ../event0
pi@cosmac:~ $ ls -l /dev/input/by-path/
total 0
lrwxrwxrwx 1 root root 9 May 14 20:23 platform-3f980000.usb-usb-0:1.4:1.0-event-kbd -> ../event0
pi@cosmac:~ $ ls -l /dev/input/event0
crw-rw---- 1 root input 13, 64 May 14 20:23 /dev/input/event0

pi@cosmac:~ $ cat /dev/input/event0 | hexdump -C

ESC
00008010  cb d9 f9 5a cc fd 04 00  04 00 04 00 29 00 07 00  |...Z........)...|
00008020  cb d9 f9 5a cc fd 04 00  01 00 01 00 01 00 00 00  |...Z............|
00008030  cb d9 f9 5a cc fd 04 00  00 00 00 00 00 00 00 00  |...Z............|
00008040  cb d9 f9 5a b8 7a 05 00  04 00 04 00 29 00 07 00  |...Z.z......)...|
00008050  cb d9 f9 5a b8 7a 05 00  01 00 01 00 00 00 00 00  |...Z.z..........|
00008060  cb d9 f9 5a b8 7a 05 00  00 00 00 00 00 00 00 00  |...Z.z..........|

Ctrl
00008070  cf d9 f9 5a 66 55 06 00  04 00 04 00 e0 00 07 00  |...ZfU..........|
00008080  cf d9 f9 5a 66 55 06 00  01 00 1d 00 01 00 00 00  |...ZfU..........|
00008090  cf d9 f9 5a 66 55 06 00  00 00 00 00 00 00 00 00  |...ZfU..........|
000080a0  cf d9 f9 5a 94 f1 06 00  04 00 04 00 e0 00 07 00  |...Z............|
000080b0  cf d9 f9 5a 94 f1 06 00  01 00 1d 00 00 00 00 00  |...Z............|
000080c0  cf d9 f9 5a 94 f1 06 00  00 00 00 00 00 00 00 00  |...Z............|

How to get and build the RaspiElf Keypad/Display Software

The elfdisplay is part of the tools package. See RaspiElf#How_to_get_and_build_the_RaspiEl

Sample session