Playing an effect while a button is held

A button that shows an effect for as long as it is held, and drops back to a standby effect when it is let go. A magician's quick-change tricks, a foot pedal on a stage, a "press for sparkle" button on a sculpture: each is the same setup, done with configuration only.

New here? Start with Install & first light. What follows assumes MoonLight is running and the buttons are wired to GPIOs.

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How it works

Three pieces, each already on every board:

• Layers stack. A bottom layer, Standby, always shows. Above it, one layer per trick has its opacity at 0, so it shows nothing until its opacity rises.
• The Control card's faders each drive one control. Fader 1 drives Trick1.opacity, fader 2 Trick2.opacity, and so on.
• The Button service turns a GPIO into a surface control. A row of kind set writes its value while the button is held and 0 when it is released.

Held, button 1 puts 255 on fader 1, so Trick1 covers Standby. Released, fader 1 goes to 0 and Standby shows again. Every effect keeps running and stays adjustable on the fly, so nothing is timed the way a playlist is.

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Setting it up

The whole setup is one state document, sent once with PATCH /api/state, or built by hand in the UI. This one has two tricks on GPIO 4 and 5. The effects, the pins and the number of tricks are yours to change, up to the eight faders the Control card has.

{
  "Effects": {
    "$patch": "replace",
    "Standby": { "type": "Layer", "Noise": { "type": "NoiseEffect" } },
    "Trick1": { "type": "Layer", "opacity": 0, "Spiral": { "type": "SpiralEffect" } },
    "Trick2": { "type": "Layer", "opacity": 0, "Fire": { "type": "FireEffect" } }
  },
  "Control": { "fader1Target": "Trick1.opacity", "fader2Target": "Trick2.opacity" },
  "Services": {
    "Buttons": {
      "type": "ButtonService",
      "buttons": [
        { "pin": 4, "activeLow": true, "target": "Control.fader1", "kind": "set", "value": 255 },
        { "pin": 5, "activeLow": true, "target": "Control.fader2", "kind": "set", "value": 255 }
      ]
    }
  }
}

curl -X PATCH -H "Content-Type: application/json" -d @hold-to-play.json http://<device>/api/state

activeLow is on for a button wired to ground; the Button card's pressed readout shows each press before anything is bound to it.

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Choosing the buttons

What you hold	Works	Why
Wired buttons or a foot pedal	yes	each is a contact on a GPIO, with a press and a release
A wireless RF remote whose receiver has momentary outputs, such as a 433 MHz module with 4 or 8 channels	yes	the receiver's outputs are wired to the GPIOs and act as buttons
An infrared remote	no	it reports a press but no release, so nothing would clear the trick

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Going further

• A softer change: a value below 255 blends the trick over Standby instead of covering it.
• Logic of its own, such as another standby after a certain trick, or a sequence on one press: a MoonLive service script drives the same controls.