Summary

This is my personal ZMK configuration for 34-key Cradio (Hypergolic). It uses contextual hold-tap configuration to make home row modifiers easier to use, along with simple macros to manage the keymap.

 
 

Contextual Hold-Taps

ZMK's interrupt based input detection offers a large number of configuration options for managing hold or tap keys. These are my contextual configuration setup for ease of triggering modifiers while avoiding false positives.

Home row non-Shift modifiers

Modifiers should not be triggered when a mod-tap key is pressed together with another key on the same hand. However, they should be triggered when held down and another key is tapped with the opposite hand. This is accomplished using tap-preferred flavor with the following positional hold-tap behavior (mirrored for the right side):

lmt: left_mod_tap {
    label           = "left_mod_tap";
    compatible      = "zmk,behavior-hold-tap";
    flavor          = "tap-preferred";
    tapping-term-ms = <TAPPING_TERM>;
    quick-tap-ms    = <QUICK_TAP>;
    global-quick-tap;
    #binding-cells  = <2>;
    bindings        = <&kp>, <&kp>;
    hold-trigger-key-positions = <
                     5  6  7  8  9
             13     15 16 17 18 19
                    25 26 27 28 29
             30 31  32 33
    >;
};
rmt: right_mod_tap {
    label           = "right_mod_tap";
    compatible      = "zmk,behavior-hold-tap";
    flavor          = "tap-preferred";
    tapping-term-ms = <TAPPING_TERM>;
    quick-tap-ms    = <QUICK_TAP>;
    global-quick-tap;
    #binding-cells  = <2>;
    bindings        = <&kp>, <&kp>;
    hold-trigger-key-positions = <
     0  1  2  3  4
    10 11 12 13 14     16
    17 21 22 23 24
             30 31  32 33
    >;
};

A mod-tap key will send its tap key code if it overlaps with another key index that is not in the hold-trigger-key-positions. If it overlaps with a key index listed in the hold-trigger-key-positions, the mod-tap behavior will be as defined. Two home row mod positions on the same side is included to allow chording of frequently used modifiers. The global-quick-tap setting is also defined to disable the hold function while typing quickly.

Home row Shift

The home row mod-tap Shift key is configured differently than the other modifiers. It is set with the balanced flavor, but only for keys on the opposite hand using hold-trigger-key-positions. The global-quick-tap feature is excluded to avoid Shift from being deactivated while typing quickly. They are configured with the following binding (also mirrored for the right side):

lst: left_shift_tap {
    label           = "left_shift_tap";
    compatible      = "zmk,behavior-hold-tap";
    flavor          = "balanced";
    tapping-term-ms = <TAPPING_TERM>;
    quick-tap-ms    = <QUICK_TAP>;
    #binding-cells  = <2>;
    bindings        = <&kp>, <&kp>;
    hold-trigger-key-positions = <
                     5  6  7  8  9
                    15 16 17 18 19
                    25 26 27 28 29
             30 31  32 33
    >;
};
rst: right_shift_tap {
    label           = "right_shift_tap";
    compatible      = "zmk,behavior-hold-tap";
    flavor          = "balanced";
    tapping-term-ms = <TAPPING_TERM>;
    quick-tap-ms    = <QUICK_TAP>;
    #binding-cells  = <2>;
    bindings        = <&kp>, <&kp>;
    hold-trigger-key-positions = <
     0  1  2  3  4
    10 11 12 13 14
    20 21 22 23 24
             30 31  32 33
    >;
};

Thumb keys

Layer-tap keys are shared with Tab and Backspace, and they are typically not "rolled" with other overlapping key presses. The &lt binding is modified with the hold-preferred flavor for quicker layer activation

&lt {
    flavor          = "hold-preferred";
    tapping-term-ms = <TAPPING_TERM>;
    quick-tap-ms    = <QUICK_TAP>;
};

The Ctrl+Alt mod-tap key with Enter is configured with the balanced flavor to allow intentional trigger of both modifiers with another overlapping key press. The &mt binding is changed to the following:

&mt {
    flavor          = "balanced";
    tapping-term-ms = <TAPPING_TERM>;
    quick-tap-ms    = <QUICK_TAP>;
};

Lastly, a hold-tap behavior is setup for Shift with Space thumb key and clipboard shortcuts. These keys are subjected to frequent overlap with other keys, so the tap-preferred flavor is used to ensure that taps are triggered even if they are pressed together with other keys to avoid false positives.

ht: hold_tap {
    label           = "hold_tap";
    compatible      = "zmk,behavior-hold-tap";
    flavor          = "tap-preferred";
    tapping-term-ms = <TAPPING_TERM>;
    quick-tap-ms    = <QUICK_TAP>;
    #binding-cells  = <2>;
    bindings        = <&kp>, <&kp>;
};

 
 

Preprocessor Macros

Home row mod-taps

A wrapper macro is used to apply the aforementioned home row mod-taps to the keymap in a way that makes them easier to read:

#define HRML(k1,k2,k3,k4) &lmt LCTRL k1  &lmt LALT k2  &lmt LGUI k3  &lst LSHFT k4
#define HRMR(k1,k2,k3,k4) &rst RSHFT k1  &rmt RGUI k2  &rmt RALT k3  &rmt RCTRL k4

Combos

Combos are simplified into one-liners using the following code:

#define COMBO(name, keypress, keypos) \
    combo_##name {                    \
        layers = <0>;                 \
        timeout-ms = <20>;            \
        bindings = <keypress>;        \
        key-positions = <keypos>;     \
    };

COMBO(name, bindings, key positions)

Macros

Macros are also simplified into one-liners using the following code:

#define MACRO(name, keys)                  \
    name: name##_macro {                   \
        label = #name;                     \
        compatible = "zmk,behavior-macro"; \
        wait-ms = <1>;                     \
        tap-ms = <1>;                      \
        #binding-cells = <0>;              \
        bindings = <keys>;                 \
    };

MACRO(dir_up, &kp DOT &kp DOT &kp FSLH)

 
 

Useful Links

• nice!nano v2 Pinout
• Customizing ZMK
• Hypergolic PCBs
• Sockets
• Keymapviz
• Keymap Drawer

Hardware Parts

• Machined header sockets
• Mill-Max 315-43-164-41-001000 sockets
• Mill-Max connector pins
• 301230 Li-po batteries
• MSK-12C02 SMD Switch
• Silicone bumper feet
• Kailh gchoc v1 switches