PWM

PWM repeatedly switches a pin at a selected frequency. It is useful for LED brightness, buzzers, and devices that accept a duty-controlled input.

Fade The Built-In LED

channel is pwm.open: $led_builtin, 1000

repeat 21 as i [
  pwm.write: channel, i * 500
  wait: 30
]

pwm.write: channel, 0
pwm.close: channel
set channel to nil

The electrical brightness direction follows the LED’s polarity. On an active-low built-in LED, a larger duty may look dimmer rather than brighter.

Word Table

Frequency And Duty

channel is pwm.open: 4, 5000
pwm.write: channel, 2500  -- 25 percent duty
pwm.write: channel, 7500  -- 75 percent duty

The duty scale is always Frothy’s inclusive 0..10000 contract. Frequency is specified in hertz. The target maps those values onto its hardware PWM peripheral; unsupported pins, frequencies, or exhausted channels return an error.

pwm.write changes the duty of an open channel. Values below 0 or above 10000 are rejected rather than clamped.

Which Pins Can PWM

Any output-capable GPIO can carry PWM — the chip routes its PWM peripheral to the pin, so there is no special “PWM pin” set the way analog input is tied to particular converter pins. Two limits apply on every board:

• Input-only pins can’t. A pin with no output driver rejects pwm.open. Which pins those are is a property of your board — on the classic ESP32 DevKit V1, for example, GPIO 34, 35, 36, and 39 are input-only.
• Never drive the flash pins. The pins wired to the module’s SPI flash chip count as output-capable, so pwm.open accepts them — but driving them corrupts the firmware’s own flash bus and typically crashes the board. Check your board’s pinout for which to avoid (on classic ESP32 modules, for example, GPIO 6–11).

A pin already held by an open channel reports busy for a different frequency, and plain gpio.write / gpio.mode on it also report busy (a digital write would silently detach the pin from its PWM signal). An exact repeat of the same pwm.open returns the existing handle. Hardware channels are limited — four concurrent channels on current boards — so pwm.open beyond that returns an error until one is closed.

Handle Lifetime

pwm.open returns a volatile Handle. Close it before reusing the pin or saving the project, then replace every top-level handle binding with a durable value such as false or nil.

channel is false

to dimmer.open [
  set channel to pwm.open: 4, 1000
]

to dimmer.close [
  pwm.close: channel
  set channel to false
]

boot is fn [ dimmer.open: ]

For precisely timed, finite high/low spans rather than a repeating duty cycle, use Digital signals . The Fade an LED tutorial develops a complete PWM project.