Pulse Out

A general-purpose per-pulse GPIO output. One module covers piezo, small speaker via a transistor, LED, and attenuated line-out into a powered speaker. Single edge or resonant burst, configurable polarity, all non-blocking.

This is the lightweight cousin of the Audio Tick output: no I2S, no amplifier IC, no synthesis. A real mechanical tick per pulse, available on every ESP build.

Included in every shipped ESP build. Disabled by default; set the pin and enable it from Config > Pulse Out after flashing.

Settings

Pref Range Default Notes
enable 0 / 1 0 Takes effect on save, no reboot needed.
pin -1 to max -1 GPIO driving the load. -1 keeps the pin idle.
mode 0 / 1 / 2 0 0 = single pulse, 1 = resonant burst, 2 = LED fade.
pulse_us 100-50000 500 Single-pulse width in microseconds. Sub-ms for audio, several ms for LEDs.
freq 1000-8000 3500 Burst frequency in Hz. For a piezo, match its marked resonance.
cycles 1-10 3 Cycles per burst. More = louder + slightly longer.
polarity 0 / 1 0 0 = active high (most cases). 1 = active low (common-anode LEDs, inverted MOSFET drivers).
fade_shift 2-4 3 Fade decay rate. 2 ≈ 100 ms total, 3 ≈ 250 ms, 4 ≈ 500 ms.

Output is rate-limited to 20 clicks/second. At high CPS the audio thins out while the counter still tracks every pulse.

Per-device voice variation

Each device picks a small offset on pulse_us and freq based on its chip ID, so two units next to each other sound subtly different rather than identical.

Same module, different load. Wire an LED (with current-limit resistor) to the chosen GPIO and pick a mode:

  • mode=0, pulse_us=5000 to 20000 (5-20 ms): visible hard flash per click.
  • mode=2 (LED fade): full brightness on each click, then exponential decay via PWM. Looks like a Geiger-counter afterglow. fade_shift controls the decay rate (2 ~100 ms, 3 ~250 ms, 4 ~500 ms).
  • polarity=0 if the LED’s anode is on the GPIO side, polarity=1 if the cathode is on the GPIO side (common-anode wiring).

Note: fade mode is LED only. Feeding PWM into a piezo or speaker would produce a soft sustained tone, not a click.

Fade mode overlaps the built-in Blip LED. Both ship; pick whichever fits your wiring. Blip LED lives on the board’s dedicated pin, Pulse Out on any GPIO you choose.

Patterns

Audio jack into a powered speaker

Use when you already have a desk speaker or aux input. Attenuate 3.3 V down to roughly line level and AC-couple.

GPIO ---[R1: 10 kohm]---+---[C1: 1 uF]---o tip
                        |
                      [R2: 4.7 kohm]
                        |
                       GND --------------o sleeve
Part Why
R1 + R2 Voltage divider: 3.3 V x 4.7 / (10 + 4.7) ~= 1.05 V, consumer line level.
C1 Blocks the divider’s DC bias so the line-in only sees the click transient. Non-polar 1 uF.

Recommended settings: mode=0, pulse_us=500. The powered speaker’s amp shapes the click.

Piezo disc or passive buzzer module 

GPIO ----+---- Piezo lead 1
              Piezo lead 2 ---- GND

No extra parts. Volume tier depends on the piezo:

  • Bare ceramic disc: wristwatch tick.
  • Passive buzzer module (disc in a plastic Helmholtz cavity): distinct tick across a small room.

Active buzzers (the “5 V buzzer module” kind with an internal oscillator) will not work in click mode. They can only buzz while powered. Look for “passive” piezos.

Recommended settings:

  • Quietest, sharpest: mode=0, pulse_us=500.
  • Loudest at 3.3 V: mode=1, cycles=3, freq= whatever’s marked on the piezo (typical: 2700, 3500, 4000 Hz).

Small speaker via MOSFET

Use when you want room-filling clicks. The MOSFET sources current from a 5 V rail so the speaker isn’t limited to what a GPIO can sink.

GPIO ---[220 ohm]--- Gate (2N7000)
                     |
                     Drain --- Speaker(-)
                               Speaker(+) --- +5 V
                                              ^
                     Drain ---[1N4148]--------+
                                  (cathode/band toward +5V)
                     Source --- GND
Part Purpose
2N7000 (or BS170) Logic-level N-channel MOSFET; switches cleanly from a 3.3 V GPIO. TO-92.
220 ohm Gate-current limiter.
1N4148 Flyback diode across the speaker. Absorbs the inductive kick when the pulse turns off.
4-8 ohm speaker The driver.

BJT alternative: BC337 NPN with a 1 kohm base resistor. The 2N3904 also works but is quieter. Keep the flyback diode either way.

Recommended settings: mode=1, cycles=2, freq=2500. Tune freq to taste; lower sounds woodier, higher sounds tinnier.

Ideas

Some less obvious things you can do once Pulse Out is wired up.

LED fade that reads as intensity

The mode=2 exponential fade with fade_shift=3 (default) is the classic “ping and afterglow” look. Try fade_shift=4 for a longer decay (~500 ms). At high CPS the LED hovers near full brightness because each click retriggers the fade; at background CPM it settles between flashes.

High-visibility tube indicator

Pair Pulse Out with a high-current LED (or a chain of LEDs through a MOSFET driver) on a desk-mounted lamp. mode=2, fade_shift=2 (~100 ms fade) on a 1 W LED makes a desk lamp react to background radiation visibly across a room. Good for demos and classroom kit.

Click-and-flash in sync

If you’re already running Audio Tick on an ESP32, also configure Pulse Out on a free GPIO with mode=0, pulse_us=20000. Each pulse fires both at the same time, so the audible click and the visible LED flash arrive together.

Multi-station variation

Several ESPGeigers side by side (teaching kit, test fleet, sensor array): give each one Pulse Out on an LED in mode=2. The per-device voice variation gives each unit a slightly different fade decay and click width, so the array doesn’t flash in identical lockstep.

Background-CPM piezo tick

Pair a low-CPS source with mode=1, cycles=2, freq=4000 driving a passive piezo. Even at background CPM (~30/min) the piezo fires a clean short tick every couple of seconds, audible across a small room without being intrusive.

Headphone tick output

mode=0, pulse_us=300-800 straight into the attenuator pattern (10 kohm + 4.7 kohm + 1 uF, see Patterns above) plugged into headphones gives you a portable Geiger counter you can wear while the device sits on a desk. Good for field walks if the tube has decent sensitivity.

Comparison with Audio Tick

  Pulse Out Audio Tick
Platforms ESP8266 + ESP32 ESP32 only
Hardware Piezo, small speaker (via MOSFET), or line-out into a powered speaker I2S amplifier IC + speaker
Sound Mechanical tick Synthesised click with chirp + decay
Boot chime None 7 chimes + random

Run both at once if you like. They share the same 20 clicks/sec cap.

See also

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