Read a Button

The LED tutorial drove an output. This one reads an input. A button is the cleanest first input because it only has two states: pressed or not pressed.

You can do this on a plain ESP32 board with BOOT_BUTTON, or on the Froth Machine with joy.click?.

Start With The Built-In Button

On ESP32 DevKit-style boards, the boot button is active-low. Released reads high. Pressed reads low.

gpio.input: BOOT_BUTTON
gpio.read: BOOT_BUTTON

Hold the button and read again. The value should change from 1 to 0.

Wrap the electrical detail in a name:

to boot.pressed? [
  (gpio.read: BOOT_BUTTON) == 0
]

Now the rest of the code can use a boolean instead of remembering that this button is active-low.

Light The LED While Pressed

Configure the output once:

gpio.output: LED_BUILTIN

Then define one frame:

button.frame is fn [
  if boot.pressed?: [
    gpio.high: LED_BUILTIN
  ] else [
    gpio.low: LED_BUILTIN
  ]
]

Run it in a short loop:

repeat 300 [
  button.frame:;
  ms: 20
]

Hold the button. The LED follows your hand.

Detect A Press Edge

Most button programs should react once per press, not on every poll while the button is held. Store the previous state:

button.prev is false
button.led is false

Detect the transition from not pressed to pressed:

button.fell? is fn [
  here now is boot.pressed?:;
  here fresh is now and (not button.prev);
  set button.prev to now;
  fresh
]

Toggle the LED on that edge:

button.toggleFrame is fn [
  when button.fell?: [
    set button.led to (not button.led);
    if button.led [
      gpio.high: LED_BUILTIN
    ] else [
      gpio.low: LED_BUILTIN
    ]
  ]
]

Run it:

repeat 600 [
  button.toggleFrame:;
  ms: 20
]

Each press toggles once. Holding the button does not keep firing.

Froth Machine Shortcut

On the Machine, the joystick click already has a semantic helper:

joy.click?:

Use the same edge pattern:

joy.prev is false

joy.clicked? is fn [
  here now is joy.click?:;
  here fresh is now and (not joy.prev);
  set joy.prev to now;
  fresh
]

The wiring is different, but the program shape is the same: convert the raw input to a boolean, detect the transition you care about, then update visible state.