QiGong Timer

An interval meditation timer for Qi Gong (or any practice), set with the knobs and played by your own Workshop System voices.

The card counts a session of intervals. At the start, at the end of every interval and at the end of the session it sends a pulse that strikes your patched sounds: a chime for the intervals, a bell or gong for the end. It adds a calm reverb and delay to those sounds, and keeps everything completely silent in between. You set it by touch and by eye: a soft click for every step, and the LEDs show the numbers.

• Intervals: 1 to 36, each 0 to 36 minutes plus 0 to 60 seconds (shortest 10 s, longest 37 min; a session can last up to 22 hours).
• 10 seconds to settle after you press start, then a double chime: the session has begun.
• A chime at the end of every interval, a bell at the end of the session.
• Pause, resume, stop. A preview mode to tune and dial in your sounds.
• Two separate effect chains (chime and bell never mix): reverb up to 25 s, delay up to 1 s.
• The card makes no sound of its own except very soft clicks while you set it.

1. Patching

The card does not make the chime and the bell: your Workshop System does. Two voices, each struck by one of the card's pulses. The wiring is the same on every system:

Pulse Out 1 ──► Slope A input        (Slope A: Loop off, Falling)
Slope A out ──► Filter A FM
Oscillator ───► Filter A ──────────► Audio In 1      (the interval chime)

Pulse Out 2 ──► Slope B input        (Slope B: Loop off, Falling)
Slope B out ──► Filter B FM
Oscillator ───► Filter B ──────────► Audio In 2      (the end bell)

Audio Out 1 ──► mixer                (the chime, with its reverb and delay)
Audio Out 2 ──► mixer                (the bell, with its reverb and delay)

Set each filter's cutoff low (closed) so the voice is silent until its Slope opens it. Each pulse lasts 100 ms; a Slope in Falling mode jumps up on the pulse and falls away, opening and closing the filter like a strike.

The sounds themselves are up to you. Every Workshop System is a little different (calibration, analogue tolerances), so there are no knob-by-knob recipes here. Some directions that work well:

• A chime is bright, high and fairly short. Try a square or saw oscillator into the filter, a short Slope time, and the filter FM amount up enough that each strike opens the filter well above the oscillator's pitch. A little filter resonance adds a ringing "ping".
• A bell or gong is lower and longer, with partials that are not in tune with each other. That is what oscillator FM gives you: let one oscillator modulate the other (gently: a little goes a long way) and try pitch ratios that are not simple (not exactly an octave or a fifth). A longer Slope time lets it ring.
• The Ring Mod multiplies two oscillators: a quick way to clangorous, metallic tones. Try it as the bell's source, into the filter.
• Keep the filter cutoff fully down between strikes: every Workshop filter leaks a little, and the closer it is to closed, the less there is to hide (see section 6).
• Use preview mode (section 5) while you tune and dial in your sounds: the card strikes chime and bell alternately, once a second, through the effects.

Leave CV Out 1/2, CV In 1/2 and Pulse In 1/2 unpatched: the card does not use them (CV Out 1 and 2 sit at 0 V).

2. Quick start

1. Flash the card (hold the boot button, plug in USB, drag the .uf2 onto the drive that appears), then switch the power off and on. All six LEDs breathe slowly: ready.
2. Tune and dial in your sounds: triple-tap Z down for preview mode. Chime, bell, chime, bell... One tap ends it.
3. Set the timer: flip Z up. Main = number of intervals, X = minutes, Y = extra seconds (section 3). Flip Z back to the middle.
4. Start: tap Z down. The LEDs count down 10 seconds, then the double chime. Breathe.

3. Setting the timer (Z up, while stopped)

• Every step makes a soft click, a slightly different note for each knob, so you can set the timer with your eyes closed.
• The LEDs show whichever knob you touched last (the number of intervals when you first flip Z up).
• Clockwise always adds, anticlockwise always takes away.
• Flipping Z up never changes a setting. A knob only takes over once you turn it a little; from then on its position is the value. (If a knob is already at the end you want, nudge it away and back.)
• 0 minutes gives intervals of just the seconds (no LEDs). 0 minutes and 0 seconds counts as 10 seconds.
• Settings can only be changed while the timer is stopped; Z up during a session is ignored.
• At power-up: 6 intervals of 5:00. Settings are not saved when the power is off.

Reading the LEDs

The six LEDs, read like a page:

 1  2
 3  4
 5  6

Intervals and minutes, 1 to 36:

• 1 to 6: that many medium LEDs.
• Above 6, each bright LED stands for a six. The rest (1 to 6) is shown by blinking one of the bright LEDs (bright LED 1 blinking = +1, LED 2 = +2 ...) or, when there are not enough bright LEDs for that, by medium LEDs after them.
• 0 minutes: no LEDs.

Seconds: one medium LED for every 10 seconds (none = 0 s, all six = 60 s).

4. A session

A single tap acts 0.4 s after you let go (the card waits to see whether a triple tap is coming).

5. Preview mode (triple tap, while stopped)

Tap Z down three times quickly. The card strikes the chime (Pulse Out 1), then 1 s later the bell (Pulse Out 2), and so on, through the effects: tune and dial in your oscillators, filters and Slopes, and the reverb and delay (section 6), until they sound right. The LEDs show the left column for the chime's second, the right column for the bell's. One tap (or a 3 s hold) ends it.

6. Effects (Z in the middle)

Each voice has its own reverb and delay: In 1 → Out 1 (chime) and In 2 → Out 2 (bell); they never mix. The effects can be adjusted at any time with Z in the middle, also during a session.

Main chooses a page; X and Y adjust it. Main has three clear positions; anywhere else it changes nothing:

• X and Y keep their settings until you pass through them ("soft pickup"), so nothing ever jumps when you change page. When you touch X or Y, the LEDs show that setting as a bar. The bar flickers until your knob has caught the setting: turn towards it until it stops flickering, then the bar follows your knob.
• Both mix knobs fully anticlockwise = no effect at all.
• Changing the echo time while echoes ring makes them glide, like tape. Feedback never runs away: the repeats always fade.
• At power-up: a medium-long (about 8 s), darkish reverb at a moderate level; the delay is off. Not saved when the power is off.

Silence between the sounds

No Workshop System filter (or Ring Mod) closes completely: a faint tone always leaks through, and a long reverb would happily sustain it. So the card keeps its outputs completely silent except when it has just struck one of your voices: each pulse opens the way, and it closes again once that sound has faded back to the level of the leak (at the latest 20 s after the pulse). The chime and the bell themselves pass through untouched.

This means sounds you trigger by hand (a Slope's button) are not heard, whether the timer is running or not. To listen to your voices, use preview mode.

7. LEDs at a glance

Everything is kept dim on purpose: this card is used with eyes closed or the lights low.

8. Jacks

9. Troubleshooting

10. Building from source

The firmware is C++ on the Pico SDK with Chris Johnson's ComputerCard library (v0.4.0, included in lib/).

scripts/build_uf2.sh            # fetches the toolchain the first time; builds out/qi_timer.uf2 (and a 192 MHz variant)
cd host && make fast && ./test_render_fast quick       # the PC test suite (about 1 minute)

• Every tuning value is in qi_config.h; the card logic is in qi_engine.h (timer, switch, set-up, LEDs) and qi_fx.h (reverb, delay, silence keeper); qi_card.h connects them to the hardware.
• It runs at 144 MHz, with the audio on core 0 and the knobs and LEDs on core 1 (worst case 77% of the time available per sample, measured with scripts/bench_cycles.py).
• Build options: -DCARD_192MHZ=ON (not recommended: it caused a whine on CV Out 1 on at least one unit), -DCARD_KEEPER_SEND_ONLY=ON (the silence keeper only acts on the effects, the dry sound always passes).
• HANDOFF.md and docs/DESIGN_HISTORY.md tell the story of every design decision and every bug found.

Credits and licence

Designed by Joe Hedinger (isbn). Firmware written with AI assistance (Claude, Anthropic), tested on hardware by the designer.

With thanks to Tom Whitwell for creating the Workshop System.

• ComputerCard by Chris Johnson (MIT licence, see lib/ComputerCard.LICENSE).
• scripts/bench_cycles.py is adapted from the cycle counter of Matt Allison's Equanimity card (MIT licence).

MIT licence: see LICENSE.