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.

Build flag

Enabled with -DPULSE_OUT, which is set in the common [com-esp] block so every shipped ESP build includes it. The module is disabled by default (pulse.enable=0); set the pin and enable it from the **Config

pulse** page after flashing.

Cost on ESP8266 is ~360 B RAM + ~2.2 KB flash; on ESP32 ~56 B RAM + ~2.2 KB flash.

Settings (pulse pref group)

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 through a 5-token bucket. At high CPS the audio thins out while the underlying counter still tracks every pulse.

Non-blocking

Two different mechanisms keep clicks off the main loop:

  • Single pulse and LED fade run on a state machine polled at 1 ms cadence. notifyClick() flips the pin and registers a deadline; the registry loop picks up the trailing edge on a later tick.
  • Resonant burst uses Arduino’s tone(), which schedules a hardware timer (timer1 on ESP8266, LEDC on ESP32). Microsecond-precise transitions at any audible frequency, also fully non-blocking.

This matters for longer pulses (e.g. 5-20 ms LED flashes) and for high CPS, where a blocking implementation would tie up the loop and starve other modules.

Per-device voice variation

Each device picks a small offset on pulse_us and freq based on its chip ID. Two units next to each other sound subtly different rather than identical. Computed once at boot.

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).

The fade mode uses analogWrite for PWM. On ESP8266 the PWM frequency is set globally; if HV is enabled it picks HV’s frequency (smooth), if not it defaults to 1 kHz (works but a careful eye may see slight flicker on the brightest steps). On ESP32 the LEDC channel handles this natively.

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

This overlaps the existing runtime-configurable blip LED. The blip LED uses JLed for asynchronous scheduling on a build-flag-fixed or runtime-set pin; Pulse Out uses the state machine described above. Both ship; pick whichever fits your build.

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: giving your Geiger counter a voice

The patterns above cover the basics. Some less obvious things you can do once Pulse Out is wired up:

Make the LED feel like radiation

The mode=2 exponential fade with fade_shift=3 (the default) is already the classic “ping and afterglow” look that old physical Geiger counters had. Try fade_shift=4 for a longer, dreamier decay (~500 ms). At high CPS the LED hovers near full brightness because each click retriggers the fade; at background CPM the LED settles between flashes. The result reads as “intensity” without any sigma calculation.

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. Useful 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 flash arrive together. Cheap “stereo feedback” that costs one LED and one resistor.

Multi-station “wave”

If you have several ESPGeiger units side by side (a teaching kit, a fleet of test stations, a sensor array), give each one Pulse Out on an LED in mode=2. The per-device voice variation means their fades have slightly different decay characters and click widths, so the array flickers asymmetrically rather than all flashing in identical lockstep. A small detail, but it makes a group of units look alive instead of identical.

Telltale “I am alive” pip

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. Drop the buzzer into the case as a soft heartbeat for the device.

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 with the device sitting on a desk. Great for field walks if your tube has decent sensitivity.

Door / motion-sensor feel

Wire Pulse Out as mode=2 LED fade into a window-mounted bright LED or a strip of NeoPixels (drive them through a level shifter). The afterglow plus the per-device voice character makes the system feel like a science-fiction prop rather than a piece of test equipment. Lean into it.

Comparison with Audio Tick

  Pulse Out Audio Tick
Platforms ESP8266 + ESP32 ESP32 only
Hardware 1 piezo, or 1 piezo + MOSFET + speaker, or attenuator + powered speaker I2S amplifier IC + speaker
Sound Mechanical tick Synthesised click with chirp + decay
Boot chime None 7 chimes + random
CPU cost Negligible (a few digitalWrites per click, non-blocking) Moderate (per-sample synthesis, throttled)

Run both at once if you like; they share the per-pulse hook and the 20 clicks/sec throttle.

See also

This site uses Just the Docs, a documentation theme for Jekyll.