External keyboard
External Keyboard & Joystick
Two optional hardware add-ons, both auto-detected and both entirely optional — a build with them enabled runs exactly the same with nothing plugged in. Two of the newer boards also ship with their own built-in keypad instead — see Built-in keyboards.
- CardKB — an M5Stack I2C QWERTY keyboard (address
0x5F), for typing messages, names and labels without walking the on-screen letter grid. - Wired joystick — four direction contacts plus a Back button, replacing the single-button navigation on boards that have no joystick of their own.
Support by device
| Device | CardKB | Wired joystick |
|---|---|---|
| Seeed Wio Tracker L1 (OLED) | ✅ Grove connector | onboard |
| Seeed Wio Tracker L1 (E-ink) | ✅ Grove connector | onboard |
| GAT562 30S Mesh Kit | — | onboard |
| Heltec V3 (experimental) | ✅ solder to free GPIOs | ✅ solder to free GPIOs |
| Heltec V4 (experimental) | ✅ solder to free GPIOs | ✅ solder to free GPIOs |
| M5Stack Cardputer ADV (experimental) | — | built-in keyboard instead, see below |
| LilyGO T-Echo Lite + KeyShield (experimental) | — | built-in keypad instead, see below |
CardKB
Plug it into the second I2C bus (the Grove connector on the Wio Tracker L1; see Wiring for the Heltec boards). The firmware probes for it once at boot — nothing to enable in Settings.
The same bus is scanned for environment sensors, so a CardKB and a sensor can share it.
Typing
Printable characters insert straight at the cursor, bypassing the on-screen grid completely. The alphabet and T9/ABC settings do not apply — a real keyboard sends the right character already, so typing is always plain Latin ASCII regardless of what Settings › Keyboard is set to.
| Key | Action |
|---|---|
| letters / digits / symbols / space | insert at the cursor |
| Backspace | delete the character before the cursor |
| Esc | cancel / back |
| Arrows | same as the joystick |
| Enter | same as the centre button |
| Fn+Enter | submit the field — no need to find the DONE cell |
| Fn+letter | open the accent popup for that letter (e.g. Fn+A → á à ä ã…) |
| Tab | the Hold-Enter equivalent, everywhere — context menus, shift-lock, clear-all |
| Fn+Esc | lock / unlock the device (single press, works in both directions) |
Fn+Esc rather than the adjacent Fn+Backspace on purpose: Fn and Backspace sit next to each other on CardKB's layout and would be far too easy to hit by accident. See Screen Lock for the physical button equivalent.
Ext. KB — Full vs Compact
Settings › Keyboard › Ext. KB picks how the on-screen keyboard behaves while a CardKB is doing the typing.
| Mode | Behaviour |
|---|---|
| Full (default) | The letter grid stays on screen. Arrows and Enter drive the grid exactly as physical buttons do, so CardKB and the joystick can be used interchangeably. |
| Compact | The grid, the special-row icons and the status line are all hidden — only the text being typed and two shortcut hints remain. Arrows move the text cursor directly, and plain Enter submits the field (same as Fn+Enter). |
Compact is designed to need no joystick at all, which makes it the right choice on a board where CardKB is the only input device — for example a Heltec V3/V4 with no joystick soldered on. In that case set it once and forget it.
Cursor mode and the accent / placeholder popups draw their own visible feedback, so they behave identically in both modes.
Wired joystick
Four direction contacts plus a separate Back button. Each contact simply shorts its pin to ground — the firmware enables the internal pull-ups, so no external resistors are needed.
- The board's existing user button (PRG on the Heltec boards) stays the centre / Enter press.
- Back is not optional: the UI uses it unconditionally once the joystick is enabled. Triple-clicking Back toggles the buzzer.
- Settings › Display › Joystick rotation rotates the direction mapping at runtime (0–3), for a stick mounted sideways in a custom enclosure. It is independent of display rotation.
Wiring (Heltec V3 / V4)
Neither board ships with a joystick or a keyboard header, so both are soldered to free GPIOs. V3 and V4 are pin-compatible per Heltec's documentation and the solo builds use the same assignment for both — confirmed working on real V4 hardware; still worth checking against your own V3 module before soldering.
| Function | GPIO | Notes |
|---|---|---|
| CardKB SDA | 3 | second I2C bus (Wire1) — not the OLED's 17/18 |
| CardKB SCL | 4 | |
| Joystick UP | 23 | |
| Joystick DOWN | 6 | |
| Joystick LEFT | 47 | |
| Joystick RIGHT | 48 | |
| Back button | 33 | required when the joystick is enabled |
| Centre / Enter | 0 | the onboard PRG button — nothing to wire |
Everything above lives in the [env:Heltec_v3_companion_solo_dual] /
[env:heltec_v4_companion_solo_dual] blocks in
variants/heltec_v3/platformio.ini
and variants/heltec_v4/platformio.ini,
with comments explaining which pins are safe to reuse. To build a CardKB-only
device, comment out the joystick block and set Ext. KB to Compact.
Built-in keyboards (Cardputer ADV, T-Echo Lite + KeyShield)
Experimental — newly-added board support, not the CardKB/joystick add-ons above. Both keypads are TCA8418-based and share one polling path, entirely independent of the CardKB code — a board can have either, or neither.
- M5Stack Cardputer ADV — built-in QWERTY, no CardKB or joystick needed.
- LilyGO T-Echo Lite + KeyShield — the KeyShield add-on gives the T-Echo Lite a T9 keypad; without it the board has no usable input for the solo UI.
Neither keypad follows CardKB's exact Fn-shortcut table (Fn+Enter,
Fn+letter accent popups, Tab, Fn+Esc lock) — see each board's own
platformio.ini / keyboard driver under variants/ for its current keymap.