Lunt

MIDI-enabled controller for dimmable AC light bulbs, with on-device manual control.

Lunt drives up to four 110/220 V dimmable bulbs through an AC dimmer module. A toggle switch selects between MANUAL (set each bulb’s brightness by hand, or over MIDI) and ANIMATION (pick from self-running light shows). An 8-LED NeoPixel strip is the on-device display — warm yellow in MANUAL, red in ANIMATION.

▶ Live animation preview — an interactive simulation of all 8 light shows on four Edison-style bulbs, no hardware needed.

How it works

An Arduino Nano controls the four channels of an AC Light Dimmer Module via phase-cut dimming (the Dimmable Light library, synced to the AC zero-cross on D2), and reads MIDI on its hardware serial port.

The toggle switch picks the mode:

• MANUAL — the encoder sets brightness; pressing it cycles the target (all bulbs or one). MIDI notes/CC also set brightness. The strip is warm yellow and shows the target.
• ANIMATION — pick one of 8 self-running animations from a menu and the bulbs play it with no input needed. The encoder tunes the animation; a MIDI clock, if present, locks it to the beat. The strip is red.

Controls

MANUAL mode

| Control | Action | | — | — | | Turn encoder right / left | Brighter / dimmer (the selected target) | | Press encoder | Cycle the target: ALL → 1 → 2 → 3 → 4 → STRIP → TEMPO → SUBDIV (defaults to ALL) |

After the four bulbs there are three setting targets (turn the encoder to adjust each):

• STRIP — the NeoPixel indicator’s overall brightness (a warm-yellow bar that dims/ brightens live). Persists into ANIMATION mode too; floored by STRIP_BRIGHTNESS_MIN.
• TEMPO — toggle the tempo/clock indicator on/off (right = on, left = off). Shown as the far-right pixel lit blue when enabled.
• SUBDIV — toggle the subdivision indicator on/off. Shown as the second-from-right pixel lit orange when enabled.

No MIDI/clock info is shown on the strip in MANUAL mode itself — only these toggles.

MIDI also drives brightness here (channel 15 by default, MIDI_CHANNEL in the sketch):

The strip is warm yellow: ALL lights every pixel, Light N lights the Nth pixel (counted from the left). While you turn the encoder it shows a brightness bar, then reverts to the pixel number.

Entering MANUAL mode resets all bulbs to mid brightness (MANUAL_RESET_BRIGHTNESS), so nothing stays stuck at whatever level an animation left it.

ANIMATION mode

The strip is red. Each of the 8 animations sits on one of the 8 pixels. See them all in the live animation preview.

Here each of the six beats is one count of the 6/8 measure, so one free-run beat = one flash; 6/8 Pulse defaults to 120 BPM (the other animations default to ~135).

MIDI clock: when a clock is running, the animation beat-locks and the encoder selects the subdivision — 1 bar · 1/2 · 1/4 · 1/8 · 1/16 (shown as 1–5 red pixels). With no clock, the encoder sets a free speed of 20–250 BPM (shown as a red bar). MIDI notes/CC are ignored in ANIMATION mode.

Clock indicators (right two pixels, while an animation is running):

• Tempo (far-right): flashes each unit — blue at the selected free-run speed (BPM), or purple on each beat when a MIDI clock is present.
• Subdivision (second from right): orange, flashing at the selected subdivision rate — only when a clock is present.

Each can be turned off via the MANUAL TEMPO / SUBDIV targets. If the tempo pixel never turns purple while you send clock, the Arduino isn’t receiving it (see Troubleshooting).

Hardware

What you need

• 1x Arduino Nano
• 1x AC Light Dimmer Module, 4 channel
• 4x Dimmable light bulbs
• 4x Bulb sockets
• 4x Light stands
• 1x Rotary encoder with push button (e.g. KY-040)
• 1x 8-LED NeoPixel (WS2812) strip
• 1x 2-way toggle switch
• 1x MIDI female DIN jack
• 2x 220 ohm resistor
• 1x 4.7k resistor
• 1x 1N914 diode
• 1x 6N138 Optocoupler
• Protoboard, wires, soldering iron

⚠️ The dimmer module switches mains AC. Wire and enclose the AC side carefully.

Wiring

All control pins are on the Arduino Nano:

Power: dimmer module and NeoPixel VCC/GND to the Nano’s 5V/GND; encoder and switch grounds to GND.

MIDI input is an opto-isolated circuit (6N138 + 1N914 + 4.7k + 220 ohm) feeding the Nano’s RX (D0). See the SparkFun MIDI tutorial for the standard input schematic.

Mode switch logic: with the internal pull-up, the switch idles HIGH (= MANUAL) and reads LOW when closed to GND (= ANIMATION). Flip ANIM_MODE_LEVEL in the sketch if your two modes come out reversed.

Software

lunt.ino

Lunt Arduino script.

Adjustable knobs are grouped in the CONFIG / KNOBS section at the top of the sketch. See Tunable parameters for the full list with values and ranges.

Libraries

Install via the Arduino Library Manager:

• MIDI Library (FortySevenEffects)
• Adafruit NeoPixel
• Dimmable Light for Arduino

Build with the Arduino AVR Boards core 1.8.3 — see Troubleshooting for why.

Board settings

• Board: Arduino Nano (Tools → Board → Arduino AVR Boards → Arduino Nano)
• Processor: ATmega328P, or ATmega328P (Old Bootloader) on most CH340 clones
• Port: the CH340 / USB-serial port (not a Bluetooth port)

Tunable parameters

All are const (or #define) in the CONFIG / KNOBS block at the top of lunt.ino, except where noted. Pins are in the Wiring table. “Range” is the sensible working range, not the data-type limit.

Modes & input

| Variable | Value | Range | Description | | — | — | — | — | | ANIM_MODE_LEVEL | LOW | LOW / HIGH | Switch level that selects ANIMATION (the other position is MANUAL). | | ENCODER_STEP | 8 | 1–32 | Brightness / free-speed change per encoder detent. | | BUTTON_DEBOUNCE_MS | 200 | 50–500 | Minimum ms between accepted encoder-button presses. | | LONG_PRESS_MS | 600 | 300–1500 | Hold time to exit an animation (shorter = a re-sync). | | MANUAL_RESET_BRIGHTNESS | 128 | 0–255 | All bulbs reset to this level when MANUAL mode is entered. |

MIDI (MANUAL mode)

| Variable | Value | Range | Description | | — | — | — | — | | MIDI_CHANNEL | 15 | 1–16 | Channel the controller listens on. | | NOTE_LIGHT[4] | 60, 61, 62, 63 | 0–127 each | Note numbers that turn bulbs 1–4 on/off. | | NOTE_MIN_BRIGHT | 40 | 0–255 | Brightness of a note played at the softest velocity. | | CC_LIGHT[4] | 22, 23, 24, 25 | 0–127 each | CC numbers that set bulbs 1–4 brightness. | | CC_ALL_BRIGHT | 27 | 0–127 | CC number that sets all bulbs at once. |

Strip

| Variable | Value | Range | Description | | — | — | — | — | | NUM_PIXELS | 8 | 1–~60 | Number of LEDs on the strip; set to match yours. | | STRIP_BRIGHTNESS_DEFAULT | 60 | 0–255 | Indicator brightness at boot (live-adjustable via the MANUAL STRIP target). | | STRIP_BRIGHTNESS_MIN | 5 | 0–60 | Floor for the STRIP brightness control so the indicator stays visible. | | COLOR_WARM | (255,130,15) | any RGB | MANUAL-mode strip color (set in setup()). | | COLOR_RED | (255,0,0) | any RGB | ANIMATION-mode strip color (set in setup()). | | MANUAL_BRIGHT_SHOW_MS | 1200 | 500–3000 | How long the brightness bar shows after a turn before reverting. |

Animation timing

| Variable | Value | Range | Description | | — | — | — | — | | ANIM_BPM_MIN | 20 | 5–120 | Free-run speed (BPM) at encoder fully left. One beat = one step / one cycle. | | ANIM_BPM_MAX | 250 | 120–600 | Free-run speed (BPM) at encoder fully right. The knob is linear in BPM. | | TAIL_SHIFT | 2 | 1–4 | Comet/larson/twinkle tail fade: b -= b >> this (smaller = longer tail). | | CLOCK_TIMEOUT_MS | 600 | 300–2000 | Clock is treated as absent (→ free speed) after this gap. | | CLOCK_BLINK_MS | 90 | 30–250 | How long the purple clock indicator stays bright on each beat. |

Beat-lock subdivisions are fixed in SUBDIV_BEATS (1 bar, 1/2, 1/4, 1/8, 1/16).

Troubleshooting

Compile fails: multiple definition of 'std::nothrow'

The full error looks like new.cpp.o ... multiple definition of 'std::nothrow' ... ArduinoSTL/new_handler.cpp.o ... first defined here.

Cause: the Dimmable Light library depends on ArduinoSTL, which redefines operator new / std::nothrow already provided by the Arduino AVR Boards core 1.8.4 and newer, so the linker sees two definitions.

Fix: downgrade the core to 1.8.3, the last version that links cleanly with ArduinoSTL: Tools → Board → Boards Manager → search “Arduino AVR Boards” → pick version 1.8.3 → Install. Re-select the Nano afterwards and recompile.

Upload fails: avrdude: stk500_recv(): programmer is not responding

Cause #1 — the MIDI input is on RX. MIDI uses the Nano’s hardware serial (D0/D1), the same UART the bootloader uses to receive the program. If the MIDI input circuit is connected to RX (D0), it blocks the upload. Fix: disconnect whatever is wired to D0 (RX) before uploading, then reconnect it afterward. (This is inherent to using hardware serial for MIDI — you’ll do it every flash.)

Cause #2 — wrong bootloader. Most CH340-based Nano clones ship with the old bootloader. Fix: select Tools → Processor → ATmega328P (Old Bootloader) and upload again.

Also check the Serial Monitor is closed (it holds the port) and that the correct CH340/USB-serial port is selected.

Brightness jumps around when turning the encoder

Mechanical rotary encoders bounce, and EMI from the nearby AC dimmer makes it worse. The sketch already decodes the encoder with a quadrature state table that rejects bounce. If it still twitches, add a 100 nF capacitor from each encoder pin (CLK, DT) to GND for hardware debouncing.

Encoder direction or strip fill is backwards

Flip the right test in handleEncoder() to reverse the knob direction; the strip’s left/right mapping is in fillPixels() / lightOnePixel().

MIDI clock isn’t detected (animations don’t beat-lock)

First check the clock indicator: enter an animation (ANIMATION mode → press the encoder) and watch the far-right pixel — it turns purple and flashes on the beat when a clock is arriving. If it stays blue (or dark):

• Enable clock output on the source. Most DAWs/keyboards don’t send MIDI clock by default — turn on “send MIDI clock / sync” for the correct port.
• Press play. Many sources only send clock while the transport is running; just changing the tempo number sends nothing.
• Confirm the MIDI input circuit is wired to RX (D0) and working (notes work in MANUAL mode is a good check).

If the indicator is purple but tempo seems to do nothing: make sure you’ve entered an animation (pressed the encoder), since the clock only drives a running animation, and that you’re watching a tempo-sensitive one (e.g. comet or 6/8 pulse).