Crate pwm_pca9685

source ·
Expand description

This is a platform agnostic Rust driver for the PCA9685 PWM/Servo/LED controller, based on the embedded-hal traits.

This driver allows you to:

Introductory blog post

§The device

This device is an I2C-bus controlled 16-channel, 12-bit PWM controller. Its outputs can be used to control servo motors or LEDs, for example.

Each channel output has its own 12-bit resolution (4096 steps) fixed frequency individual PWM controller that operates at a programmable frequency from a typical of 24 Hz to 1526 Hz with a duty cycle that is adjustable from 0% to 100%. All outputs are set to the same PWM frequency.

Each channel output can be off or on (no PWM control), or set at its individual PWM controller value. The output driver is programmed to be either open-drain with a 25 mA current sink capability at 5 V or totem pole with a 25 mA sink, 10 mA source capability at 5 V. The PCA9685 operates with a supply voltage range of 2.3 V to 5.5 V and the inputs and outputs are 5.5 V tolerant. LEDs can be directly connected to the outputs (up to 25 mA, 5.5 V) or controlled with external drivers and a minimum amount of discrete components for larger current, higher voltage LEDs, etc. It is optimized to be used as an LED controller for Red/Green/Blue/Amber (RGBA) color backlighting applications.

Datasheet: PCA9685

§Usage examples (see also examples folder)

To use this driver, import this crate and an embedded_hal implementation, then instantiate the appropriate device.

Please find additional examples in this repository: driver-examples

§Create a driver instance

use linux_embedded_hal::I2cdev;
use pwm_pca9685::{Address, Pca9685};

let dev = I2cdev::new("/dev/i2c-1").unwrap();
let address = Address::default();
let pwm = Pca9685::new(dev, address).unwrap();
// do something...

// get the I2C device back
let dev = pwm.destroy();

§Create a driver instance for the PCA9685 with an alternative address

use linux_embedded_hal::I2cdev;
use pwm_pca9685::{Address, Pca9685};

let dev = I2cdev::new("/dev/i2c-1").unwrap();
let (a5, a4, a3, a2, a1, a0) = (false, true, false, true, true, false);
let address = (a5, a4, a3, a2, a1, a0);
let pwm = Pca9685::new(dev, address).unwrap();

§Set the PWM frequency and channel duty cycles

  • Set a PWM frequency of 60 Hz (corresponds to a value of 100 for the prescale).
  • Set a duty cycle of 50% for channel 0.
  • Set a duty cycle of 75% for channel 1 delayed 814 µs with respect to channel 0.
use linux_embedded_hal::I2cdev;
use pwm_pca9685::{Address, Channel, Pca9685};

let dev = I2cdev::new("/dev/i2c-1").unwrap();
let address = Address::default();
let mut pwm = Pca9685::new(dev, address).unwrap();
pwm.set_prescale(100).unwrap();
pwm.enable().unwrap();

// Turn on channel 0 at 0 and off at 2047, which is 50% in the range `[0..4095]`.
pwm.set_channel_on_off(Channel::C0, 0, 2047).unwrap();

// Turn on channel 1 at 200, then off at 3271. These values comes from:
// 0.000814 (seconds) * 60 (Hz) * 4096 (resolution) = 200
// 4096 * 0.75 + 200 = 3272
pwm.set_channel_on_off(Channel::C1, 200, 3272).unwrap();

§Set the PWM frequency and channel duty cycles separately

  • Set a PWM frequency of 60 Hz (corresponds to a value of 100 for the prescale).
  • Set a duty cycle of 50% for channel 0.
  • Set a duty cycle of 75% for channel 1 delayed 814 µs with respect to channel 0.
use linux_embedded_hal::I2cdev;
use pwm_pca9685::{Address, Channel, Pca9685};

let dev = I2cdev::new("/dev/i2c-1").unwrap();
let address = Address::default();
let mut pwm = Pca9685::new(dev, address).unwrap();
pwm.set_prescale(100).unwrap();
pwm.enable().unwrap();

// Turn on channel 0 at 0
pwm.set_channel_on(Channel::C0, 0).unwrap();

// Turn off channel 0 at 2047, which is 50% in the range `[0..4095]`.
pwm.set_channel_off(Channel::C0, 2047).unwrap();

// Turn on channel 1 at 200. This value comes from:
// 0.000814 (seconds) * 60 (Hz) * 4096 (resolution) = 200
pwm.set_channel_on(Channel::C1, 200).unwrap();

// Turn off channel 1 at 3271, which is 75% in the range `[0..4095]`
// plus 200 which is when the channel turns on.
pwm.set_channel_off(Channel::C1, 3271).unwrap();

§Set a channel completely on and off (beware of precedences).

use linux_embedded_hal::I2cdev;
use pwm_pca9685::{Address, Channel, Pca9685};

let dev = I2cdev::new("/dev/i2c-1").unwrap();
let address = Address::default();
let mut pwm = Pca9685::new(dev, address).unwrap();
pwm.enable().unwrap();

// Turn channel 0 full on at 1024
pwm.set_channel_full_on(Channel::C0, 1024).unwrap();

// Turn channel 0 full off (full off takes precedence over on settings)
pwm.set_channel_full_off(Channel::C0).unwrap();

// Return channel 0 to full on by deactivating full off.
// The value is ignored because full on takes precedence
// over off settings except full off.
let value_ignored_for_now = 2048;
pwm.set_channel_off(Channel::C0, value_ignored_for_now).unwrap();

// Deactivate full on and set a duty cycle of 50% for channel 0.
// (on from 0 to 2047, then off)
pwm.set_channel_on(Channel::C0, 0).unwrap();

§Set a 50% duty cycle for all channels at once

use linux_embedded_hal::I2cdev;
use pwm_pca9685::{ Channel, Pca9685, Address };

let dev = I2cdev::new("/dev/i2c-1").unwrap();
let address = Address::default();
let mut pwm = Pca9685::new(dev, address).unwrap();
pwm.enable().unwrap();

let mut on = [0; 16];
let mut off = [2047; 16];
pwm.set_all_on_off(&on, &off);

§Set all channels to full on, turning on after 50% of the first cycle

use linux_embedded_hal::I2cdev;
use pwm_pca9685::{Address, ChannelOnOffControl, Pca9685};

let dev = I2cdev::new("/dev/i2c-1").unwrap();
let address = Address::default();
let mut pwm = Pca9685::new(dev, address).unwrap();
pwm.enable().unwrap();
let values = [ChannelOnOffControl {
    on: 2047,
    full_on: true,
    ..Default::default()
}; 16];
pwm.set_all_channels(&values);

§Use a programmable address

Several additional addresses can be programmed for the device (they are volatile, though). Once set it is necessary to enable them so that the device responds to them. Then it is possible to change the address that the driver uses to communicate with the device.

use linux_embedded_hal::I2cdev;
use pwm_pca9685::{Channel, Pca9685, Address, ProgrammableAddress};

let dev = I2cdev::new("/dev/i2c-1").unwrap();
let hardware_address = Address::default();
let mut pwm = Pca9685::new(dev, hardware_address).unwrap();

let subaddr1 = 0x71;
pwm.set_programmable_address(ProgrammableAddress::Subaddress1, subaddr1).unwrap();
pwm.enable_programmable_address(ProgrammableAddress::Subaddress1).unwrap();

// Now communicate using the new address:
pwm.set_address(subaddr1).unwrap();
pwm.enable().unwrap();
pwm.set_channel_on_off(Channel::C0, 0, 2047).unwrap();

// The device will also respond to the hardware address:
pwm.set_address(hardware_address).unwrap();
pwm.set_channel_on_off(Channel::C0, 2047, 4095).unwrap();

// when done you can also disable responding to the additional address:
pwm.disable_programmable_address(ProgrammableAddress::Subaddress1).unwrap();

§Put the device to sleep then restart previously active PWM channels

use linux_embedded_hal::{Delay, I2cdev};
use pwm_pca9685::{Address, Channel, Pca9685};

let dev = I2cdev::new("/dev/i2c-1").unwrap();
let mut pwm = Pca9685::new(dev, Address::default()).unwrap();
pwm.enable().unwrap();

pwm.set_channel_on_off(Channel::C0, 0, 2047).unwrap();
// Prepare for restart and put the device to sleep
pwm.enable_restart_and_disable().unwrap();
// ...
// re-enable device and reactivate channel 0
let mut delay = Delay{};
pwm.restart(&mut delay).unwrap();

§Using async driver

Enable the async feature in your Cargo.toml:

pwm-pca9685 = { version = "1.0.0", features = ["async"] }
  • Set a PWM frequency of 60 Hz (corresponds to a value of 100 for the prescale).
  • Set a duty cycle of 50% for channel 0.
  • Set a duty cycle of 75% for channel 1 delayed 814 µs with respect to channel 0.
#![no_std]
#![no_main]

use embassy_executor::Spawner;
use embassy_rp::{bind_interrupts, i2c};
use embassy_rp::peripherals::I2C0;
use pwm_pca9685::{Address, Channel, Pca9685};

bind_interrupts!(struct Irqs {
    I2C0_IRQ => i2c::InterruptHandler<I2C0>;
});

#[embassy_executor::main]
async fn main(_spawner: Spawner) {
    let p = embassy_rp::init(Default::default());
    let dev = i2c::I2c::new_async(p.I2C0, p.PIN_1, p.PIN_0, Irqs, i2c::Config::default());
    let address = Address::default();
    let mut pwm = Pca9685::new(dev, address).await.unwrap();
    pwm.set_prescale(100).await.unwrap();
    pwm.enable().await.unwrap();

    // Turn on channel 0 at 0 and off at 2047, which is 50% in the range `[0..4095]`.
    pwm.set_channel_on_off(Channel::C0, 0, 2047).await.unwrap();

    // Turn on channel 1 at 200, then off at 3271. These values comes from:
    // 0.000814 (seconds) * 60 (Hz) * 4096 (resolution) = 200
    // 4096 * 0.75 + 200 = 3272
    pwm.set_channel_on_off(Channel::C1, 200, 3272).await.unwrap();
}

Re-exports§

  • pub use nb;

Structs§

Enums§