ZMK Split Peripheral Output Relay

This module add a output relay for ZMK. This is an add-on for zmk-output-behavior-listener to broadcast output event to split peripheral(s) via bluetooth.

What it does

This module sideload a new set of GATT Service and Characteratics into existing split bt paired connection. The new characteristics allow to transfer output event from central to peripherals with a relay-channel id. Then, output events would trigger output device(s) on peripheral(s).

There is an extension module that proxies output to split peripherals via bluetooth.

You might also want to checkout this module that does opposite directional proxying for input.

Installation

Include this project on your ZMK's west manifest in config/west.yml:

manifest:
  remotes:
    # ...
    - name: badjeff
      url-base: https://github.com/badjeff
  projects:
    # ...
    # START #####
    - name: zmk-split-peripheral-output-relay
      remote: badjeff
      revision: main
    # END #######
    # ...

In below config, a DRV2605 driven LRA (<&fb_lra0>) will be triggered on peripheral shield on key press q.

Additional modules are used in below config:

• zmk-output-behavior-listener
• zmk-drv2605-driver

Update board.keymap. The detail explanation for zmk,output-behavior-listener and zmk,output-behavior-generic could be find at here.

#define OUTPUT_SOURCE_KEYCODE_STATE_CHANGE  3
/{
        lra0_obl__press_key_code_q {
                compatible = "zmk,output-behavior-listener";
                layers = < DEF LHB >;
                sources = < OUTPUT_SOURCE_KEYCODE_STATE_CHANGE >;
                position = < 0x14 >;
                bindings = < &ob_lra0 >;
        };
        ob_lra0: ob_lra0 {
                compatible = "zmk,output-behavior-generic";
                #binding-cells = <0>;
                device = <&fb_lra0>;
                force = <7>;
        };
};

Once the trigger is called, zmk,output-split-output-relay is used to intercept that event on central, and broadcast it as a payload with a relay-channel header via zmk,split-peripheral-output-relay.

Update split central devicetree file board_left.overlay:

/{
  fb_lra0: fb_lra0 {
    compatible = "zmk,output-split-output-relay";
    #binding-cells = <0>;
  };
  output_relay_config_201 {
    compatible = "zmk,split-peripheral-output-relay";
    device = <&fb_lra0>;
    relay-channel = <201>;
  };
};

On peripheral(s) side, zmk,output-split-output-relay is used to decode the payload to output event from relay-channel. And, a zmk,output-haptic-feedback or zmk,output-generic is used to reflect the event context on peripheral(s). Currently, its only supporting one output device per relay-channel on same shield, and all shield will be triggered by same event simultaneously.

Update split peripheral devicetree file board_right.overlay:

/ {
  output_relay_config_201_a {
    compatible = "zmk,split-peripheral-output-relay";
    relay-channel = <201>;
    device = <&fb_lra0>;
  };
  fb_lra0: fb_lra0 {
    compatible = "zmk,output-haptic-feedback";
    #binding-cells = <0>;
    driver = "drv2605";
    device = <&drv2605_0>;
  };
};